Zakopane 2026 Conference on Nuclear Physics

Several experiments aiming at studying the low energy parts of the Electric Dipole response (the so called Pygmy Dipole Resonance, PDR) in nuclei were carried out during the years and are presently being made. Use of different probes and techniques was made and nuclei in different mass regions were investigated.
The interest in the PDR states is related to their astrophysical implications in the nucleosynthesis and also because the underlying structure of the PDR is under active debate and scrutiny. The PDR’s isospin splitting was revealed in complementary experiments with isoscalar and isovector probes exciting states in several nuclei, suggesting that the PDR splits into a lower-energy isoscalar surface mode and a higher-energy component with an isovector admixture from IVGDR. Some possible evidence for the electric pygmy quadrupole states was also found.
More recent directions concern the search of E1 decay from states with angular momentum higher than zero and experiments detecting gamma-rays from fission products.
A difficul task is to identify pygmy states in nuclei at finite temperature and for this purpose dedicated experimental efforts are being made. Indeed, this signal is of great interest because the nucleosynthesis in the stellar environment involves nuclei which are not necessarely in the ground states.
To underline the importance of the PDR investigations selected results, open problems and future plans will be presented and discussed. Special emphasis is given to the plans with the PARIS detector arrays.

I will present selected results on nuclear giant and pygmy resonances at zero and finite temperatures based on the recent advancements of the nuclear many-body theory [1-6]. The theory will be compactly introduced in a model-independent quantum field theory framework using only the bare fermionic interaction as an input, enabling controllable approximations. A special focus will be placed on the emergent scale of the quasiparticle-vibration coupling (qPVC), with the order parameter associated with the qPVC vertex, and an efficient treatment of the nuclear many-body problem organized around the qPVC hierarchy [1-3].

Self-consistent solutions of the relativistic Bethe-Salpeter-Dyson equation for the nuclear response function will be presented and discussed. Low-multipole neutral and charge-exchange resonances in calcium, nickel, and tin mass regions will be analyzed in the context of the role of high-complexity configurations in reproducing spectral data [2,3,7]. Finite-temperature theory and implementations for astrophysically relevant low-energy dipole strength, beta decay rates, and electron capture rates will be overviewed in light of the temperature dependence of the nuclear spectral properties [4,5]. Recent developments in computing transitions between nuclear excited states, providing a microscopic alternative to statistical descriptions, will be presented as a promising new avenue for supporting both experimental programs and stellar modeling [8].

References
[1] E. Litvinova and Y. Zhang, Microscopic response theory for strongly-coupled superfluid fermionic systems, Phys. Rev. C 106, 064316 (2022).
[2] E. Litvinova, On the dynamical kernels of fermionic equations of motion in strongly-correlated media, Eur. Phys. J. A59, 291 (2023).
[3] J. Novak, M. Q. Hlatshwayo, and E. Litvinova, Response of strongly coupled fermions on classical and quantum computers, arXiv:240502255.
[4] E. Litvinova and H. Wibowo, Finite-temperature relativistic nuclear field theory: an application to the dipole response, Phys. Rev. Lett. 121, 082501 (2018).
[5] E. Litvinova, C. Robin, and H. Wibowo, Temperature dependence of nuclear spin-isospin response and beta decay in hot astrophysical environments, Phys. Lett. B800, 135134 (2020).
[6] S. Bhattacharjee and E. Litvinova, Response of superfluid fermions at finite temperature, arXiv:2412.20751, Phys. Rev. C (2026).
[7] M. Markova, P. von Neumann-Cosel, and E. Litvinova, Systematics of the low-energy electric dipole strength in the Sn isotopic chain, Phys. Lett. B860, 139216 (2025).
[8] R. Li, E. Litvinova, M. Harakeh et al., First evidence for the J>1 components of the pygmy dipole resonance in neutron-rich nuclei, arXiv:2510.27125.

Finite-temperature effects play a crucial role in shaping exotic nuclear excitations. Thermal unblocking and the weakening of pairing correlations can significantly modify excitation modes of different multipolarities, leading to the emergence of strength that is suppressed at zero temperature. A microscopic description of these effects is therefore important for nuclear structure studies and for astrophysical applications involving hot, neutron-rich systems [1–3].

In this talk, I present a unified study of nuclear excitations at finite temperature based on the finite-temperature relativistic quasiparticle random-phase approximation within the covariant energy density functional framework. I first examine how temperature affects electric and magnetic excitation modes, with emphasis on the role of pairing reduction and thermally unblocked configurations. I then discuss the temperature evolution of the pygmy dipole resonance and the emergence of thermally induced low-energy dipole strength in neutron-rich nuclei [4]. Finally, I address the consequences for electromagnetic γ-ray strength functions, highlighting the redistribution and enhancement of low-energy E1 and M1 strength relevant for hot stellar environments [5].

References
[1] E. Yüksel, G. Colò, E. Khan, Y. F. Niu, and K. Bozkurt, “Multipole excitations in hot nuclei within the finite temperature quasiparticle random phase approximation framework,” Phys. Rev. C 96, 024303 (2017).
[2] E. Yüksel, G. Colò, E. Khan, and Y. F. Niu, “Nuclear excitations within microscopic EDF approaches: Pairing and temperature effects on the dipole response,” Eur. Phys. J. A 55, 230 (2019).
[3] A. Kaur, E. Yüksel, and N. Paar, “Finite-temperature effects in magnetic dipole transitions,” Phys. Rev. C 109, 024305 (2024).
[4] A. Kaur, E. Yüksel, and N. Paar, “Hot pygmy dipole strength in nickel isotopes,” Phys. Rev. C 112, L051304 (2025).
[5] A. Kaur, E. Yüksel, and N. Paar, “Electric and magnetic γ-ray strength functions at finite temperature,” Phys. Rev. C 112, 014307 (2025).

N.S. Martorana$^{1}$, C. Cardella$^{1}$, E.G. Lanza$^{1}$, L. Acosta$^{2}$, M.V. Andrés$^{3}$, F. Camera$^{4,5}$, A. Castoldi$^{5,6}$, E. De Filippo$^{1}$, E. Geraci$^{1,7,8}$, A. Giaz$^{5}$, B. Gnoffo$^{1,7}$, C. Guazzoni$^{5,6}$, C. Maiolino$^{9}$, E.V. Pagano$^{9}$, L. Pellegri$^{10,11}$, S. Pirrone$^{1}$, G. Politi$^{1,7}$, F. Risitano$^{1,8,12}$, F. Rizzo$^{7,8,9}$, P. Russotto$^{9}$, M. Trimarchi$^{1,12}$, G. Verde$^{1}$, O. Wieland$^{5}$, C. Zagami$^{8,9}$
and the NUSDAF collaboration

1 INFN-Sezione di Catania, Catania, Italy
2 Instituto de Estructura de la Materia, CSIC, Spain
3 Departamento de FAMN, Facultad de Física, Sevilla, Spain
4 Università degli studi di Milano, Milano, Italy
5 INFN Sezione di Milano, Milano, Italy
6 DEIB Politecnico di Milano, Milano, Italy
7 Università degli Studi di Catania, Catania, Italy
8 CSFNSM, Catania, Italy
9 INFN-LNS, Catania, Italy
10 School of Physics, University of the Witwatersrand, South Africa
11 iThemba Laboratory for Accelerator Based Sciences, South Africa
12 Dipartimento MIFT, Università di Messina, Messina, Italy

The Pygmy Dipole Resonance (PDR) is a low-lying electric dipole (E1) excitation observed in neutron-rich nuclei, located around the nucleon binding energy. It is macroscopically interpreted as an oscillation of the neutron skin against the nuclear core, although its precise nature, whether collective or arising from a series of no-coherent single-particle excitations, remains an open question. A notable feature of the PDR is its isospin mixing, which allows it to be excited by both isoscalar and isovector probes [1–3]. Experimental studies have shown that the PDR can indeed be populated with both types of probes. In stable nuclei, a splitting is observed in the excitation region below the neutron separation threshold: in the low-lying region the dipole states are excited by both isoscalar and isovector probes, while in the higher-lying one only the excitation by the isovector probes is present [1–3]. This phenomenon, referred to as isospin splitting, appears to be absent in unstable nuclei, where the PDR has been measured above the neutron separation threshold [4–5]. The investigation of the PDR is of great interest not only for nuclear structure studies, but also for constraining the neutron-skin thickness, probing the symmetry energy term of EoS, and improving models of astrophysical processes such as r-process nucleosynthesis [1]. A deeper understanding of the PDR requires systematic investigations with both isoscalar and isovector probes over a wide range of nuclear isotopes and both below and above the neutron emission threshold. In this contribution, an overview of recent results on PDR studies in unstable nuclei is presented, together with future perspectives aimed at improving our understanding of this mode through the use of radioactive ion beams. In particular, future experimental campaigns at FRIB, proposed within the NUSDAF initiative, will be discussed, focusing on advanced studies of the PDR along the Ni isotopic chain through the investigation of both γ and neutron decay channels. First theoretical calculations for Ni isotopes, as well as simulation studies on the feasibility of detecting both neutron and γ decay channels, will also be presented. In addition, benefiting from the high quality and intensity of radioactive beams at FRIB, the program plans to use some existing equipment. Possible perspectives that may be offered by doing experiments at FRIB with more efficient high energy gamma detectors (such as PARIS, among others) will also be discussed.

[1] A. Bracco et al., Progr. in Particle and Nuclear Physics 106, 360-433 (2019) and references therein
[2] D. Savran et al., Progr. In Particle and Nuclear Physics 70, 210-245 (2013) and references therein
[3] E.G. Lanza et al., Progr. in Part. and Nucl. Phys.,129, 104006, (2023) and references therein
[4] O. Wieland et al., Phys. Rev. Lett. 102, 092502 (2009)
[5] N.S. Martorana et al. In: Physics Letters B 782, 112 116 (2018)

Extreme shape coexistence, of which shape isomers observed in actinide nuclei at spin zero are peculiar examples, is also at the origin of the phenomenon of superdeformation in rapidly rotating nuclei. Nevertheless, the studies of superdeformation have developed virtually in a completely independent manner from other shape-coexistence investigations, mainly because they were carried out almost always in the high-spin regime, while the others were related to low-spin phenomena [1,2].
In this talk, we will focus on Ni isotopes, where example of shape-isomer-like 0+ excitations have been found in 66Ni and 64Ni [3,4], and we will discuss new results on 62Ni, in which superdeformed rotational bands at high spin, decaying out at around spin 8, are known [5]. Following a neutron capture experiment with the FIPPS spectrometer at ILL, ten 0+ excited states below 6.5 MeV have been observed in 62Ni, with a fragmented gamma decay, in close agreement with predictions from state-of-the-art Monte Carlo Shell Model calculations. This allowed to identify, among them, the band-head of the superdeformed rotational band at high spins, which turns out to be fragmented over highly deformed and triaxial 0+ configurations.
The work allows to make a connection between shape coexistence at spin 0 and superdeformation at high spins, and to trace, microscopically, the origin of the fragmented decay pattern of the superdeformed band [6].

[1] S. Leoni, B. Fornal, A. Bracco, Y. Tsunoda, T. Otsuka, Prog. Part. Nuc. Phys. 139 (2024) 104119.
[2] S. Leoni, B. Fornal, N. Marginean, and J. N. Wilson, Eur. Phys. J. Spec. Top. 233 (2024) 1061.
[3] S. Leoni, et al., Phys. Rev. Lett. 118 (2017) 162502.
[4] N. Marginean, et al., Phys. Rev. Lett. 125 (2020) 102502.
[5] M. Albers et al., Phys. Rev. C 94 (2016) 034301.
[6] C. Costache, et al., in preparation.

In this invited contribution, I will present recent results from $(d,p)$ experiments performed with the Super-Enge Split-Pole Spectrograph at the John D. Fox Accelerator Laboratory of Florida State University [1] to study single-particle strengths in $fp$-shell nuclei [2-4]. After briefly highlighting the capabilities of the experimental setup [1,5], I will focus on three specific examples. First, I will provide a brief overview on our results obtained for the neutron-adding strengths in the $N=29$ isotone $^{53}$Cr [3], comparing to strengths measured earlier for $^{55}$Fe [6]. Then, I will pivot and focus on the rich dataset which we obtained for $^{50}$Ti. I will briefly point out similarities and differences between the fragmentation of neutron-adding strengths for excited states of even-$A$ $^{50}$Ti and odd-$A$ $^{51}$Ti, before I discuss $1^+$ and $1^-$ states of $^{50}$Ti populated in the $(d,p)$ reaction. By comparing to observables obtained from complementary experiments, I will make a case for how $(d,p)$ can be used to study the microscopic origin of the spin-flip $M1$ resonance [4] and of the low-energy $E1$ strength, often referred to as pygmy dipole resonance (PDR) [2,7].

The experimental program at the FSU John D. Fox Laboratory is supported by the U.S. National Science Foundation (PHY-2412808 and PHY-2405485) and by the U.S. National Nuclear Security Administration (DE-NA0004150) as part of CENTAUR. Support from Florida State University is gratefully acknowledged.

References:

1. M. Spieker and S. Almaraz-Calderon, Frontiers in Physics 12, 1511394 (2024).
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Collective dynamics in atomic nuclei emerge from the coherent motion of many nucleons and provide important insight into how nuclei respond to external perturbations. Resonant photon scattering, or nuclear resonance fluorescence, provides a clean and selective experimental probe of this response. Since real photons couple directly to nuclear charge and current distributions, they can excite and resolve electric and magnetic dipole modes with minimal distortion from the interaction mechanism. This talk will present recent resonant photon-scattering studies performed with quasi-monochromatic, highly polarized photon beams at the High Intensity Gamma-ray Source (HIγS) at the Triangle Universities Nuclear Laboratory. Emphasis will be placed on the use of high-resolution photon scattering to map dipole-strength distributions, identify fine structure and multipole character through polarization asymmetries and angular distributions, and extract reduced transition probabilities as well as photon-strength functions. These observables provide sensitive tests of the microscopic structure of dipole excitations, including strength fragmentation and the emergence of low-energy collectivity. The results will be confronted with state-of-the-art theoretical calculations and compared with complementary data from hadron-induced reactions. These comparisons highlight the distinct selectivity of photon beams and contribute to the interpretation of collective modes relevant to nuclear structure, reaction theory, and astrophysical applications.

The identification of vibrational dynamics in the low-lying excitation spectra of deformed nuclei continues to be an open challenge in nuclear structure physics. In algebraic, phenomenological, or geometric models, the lowest vibrational shape affecting oscillations that can be built on a deformed ground state include the quadrupole ($\lambda = 2$) and the octupole ($\lambda = 3$) modes. Quadrupole oscillations are typically described in terms of $\beta$ and $\gamma$ one-phonon vibrational modes (lowest lying K$^{\pi}=0^+$ and K$^{\pi}=2^+$ bands), and excited bands (K$^{\pi}=0^+,2^+,4^+$ bands) as $\beta\beta$, $\beta\gamma$, and $\gamma\gamma$ two-phonon excitations, that is (2$^+ \otimes 2^+$) quadrupole phonons. The quadrupole mode of oscillations along the symmetry axis result in $\beta$ vibrations with K$^{\pi}=0^+$ and those breaking axial symmetry, result in $\gamma$ vibrations with a projection of K$^{\pi}=2^+$ on the symmetry axis. The discussions on the nature of numerous low-lying bands observed in the spectra of deformed nuclei continue. Are they indeed vibrations built on the ground state? Or are they coexisting minima of other shapes? The discussions have led to a reexamination of the nature of vibrational excitations. Vibrational excitations built on the ground state of a deformed nucleus are expected to show the same degree of deformation, the same dynamic and kinetic moments of inertia with some dispersion, and where there is enough information the same intrinsic quadrupole moment for transitions from the same band connecting to the ground state band.

There are a number of two-phonon vibrational excitations identified in deformed nuclei, two-phonon $\beta\beta$ vibrational type in $^{178}$Hf, and a potential $\beta\gamma$ type in $^{162}$Dy, and several cases of potential $\gamma\gamma$, K$^{\pi}=4^+$ bands in the rare-earth region of well-deformed nuclei. The ratios of the two-phonon to one phonon vibrational excitations energies are theoretically expected to be at twice the single phonon values. The B(E2) ratios of the two-phonon $\gamma\gamma$ to single-phonon to ground state values are expected to be 2.78 for K$^{\pi}=4^+$ and 5.0 for K$^{\pi}=0^+$. Results from current measurements and interpretations will be presented and discussed.

The discovery of β-delayed neutron emission followed closely that of nuclear fission[1], and the phenomenon was quickly incorporated, into the Bohr-Wheeler compound-nucleus picture[2]. Since that era, β-delayed particle emission has been discussed largely within a two-step statistical framework (the Pandemonium theory [3]).

Over the past decade, several observations have placed this view under severe strain. Among them, unexpectedly strong γ/neutron competition above the neutron separation energy has been reported [4] [5]. An even more striking case is the β decay of the neutron-rich nucleus 83Ga, where high-energy γ emission (up to∼5–8 MeV) competes with neutron emission from states located well above threshold [6]. This extraordinary, totally unexpected behaviour was questioned , calling for a dedicated re-measurement of the high-energy part of the spectrum.

We therefore performed a dedicated experiment at the ALTO facility using the PARIS γ-ray spectrometer coupled to the BEDO decay station. The improved efficiency at high energy and the enhanced segmentation enable a more reliable characterization of the high-energy γ spectra and a more robust extraction of γ-ray intensities. Beyond the 83Ga case, we also carried out a systematic study across the N=50 region (including the β decays of 80Ga and 82Ga) in order to identify structural conditions under which dynamics beyond the purely statistical compound-nucleus description may emerge. The results will be presented and discussed in connection with a microscopic (though phenomenological) structure-driven interpretation that includes the doorway-state concept in its original sense, as introduced by Feshbach and collaborators.

[1] R. B. Roberts, L. R. Hafstad, R. C. Meyer, and P. Wang, The Delayed Neutron Emission which Accompanies Fission of Uranium and Thorium, Phys. Rev. 55, 664, April 1939.
[2] N. Bohr and J. A. Wheeler , The Mechanism of Nuclear Fission, Phys. Rev., 56:426–450, September 1939.
[3] J. C. Hardy et al., The essential decay of pandemonium, Phys. Lett. B, 71(2):307–310, November 1977.
[4] J. L. Tain et al., Enhanced γ-Ray Emission from Neutron Unbound States Populated in β Decay. Phys. Rev. Lett., 115(6), August 2015.
[5] A. Spyrou et al., Strong Neutron-γ Competition above the Neutron Threshold in the Decay of 70Co, Phys. Rev. Lett. 117, 142701, September, 2016
[6] A. Gottardo et al. , Unexpected high-energy γ emission from decaying exotic nuclei, Phys. Lett. B, 772:359–362 (2017)

Near-threshold narrow resonances in light nuclei are crucial for nuclear structure studies: they are expected to provide information on the onset of clusterization phenomena, and they also play a key role in nucleosynthesis reactions in stars. A famous example is the Hoyle state in $^{12}$C. In this context, the $\gamma$ decay from near-threshold states, with branches of the order of $10^{-3}$–$10^{-6}$ with respect to particle emission, is one of the most powerful probes of their wave function.

In this contribution we will investigate, at first, the possible existence of a narrow resonance in $^{11}$B, lying just above the proton-decay threshold, which was originally suggested to explain the observation of an unexpectedly large proton emission after the $\beta^-$ decay of $^{11}$Be [1]. An explorative experiment performed in 2021 with GALILEO+TRACE at Laboratori Nazionali di Legnaro reported an upper limit of $1.12\cdot10^{-3}$ for the $\gamma$-ray branch from this possible resonance (with limited statistical confidence) [2], slightly above theoretical predictions from the Shell Model Embedded in the Continuum (SMEC) [3,4]. More recently, in October 2025, the same $^6\text{Li}(^6\text{Li},\text{p}\gamma)$ fusion-evaporation reaction was performed using a significantly improved setup consisting in the AGATA spectrometer coupled to the upgraded highly-segmented silicon charged-particle detector TRACE [5] and the silicon CD detector SAURON. Owing to the high statistics collected, a sensitivity of $\leq10^{-4}$ on the $\gamma$-decay branching ratio is expected. The data analysis is currently ongoing, and preliminary results will be presented.

As a second case, we will briefly discuss a similar investigation carried out for $^{14}$C, which was populated through the $^9\text{Be}(^6\text{Li},\text{p}\gamma)$ fusion-evaporation reaction at Argonne National Laboratory with the GRETINA+ORRUBA setup [6]. One of the aims of the experiment was the estimate of the $\gamma$-decay branch from the $2_2^+$ state located just above the neutron separation energy. An upper limit of $4.0 \cdot 10^{-5}$ was obtained for this branch, providing an additional constraint to the theoretical interpretation of its decay properties.

[1] Y. Ayyad, B. Olaizola, W. Mittig et al., Phys. Rev. Lett. 123, 082501 (2019).
[2] S. Bottoni, G. Corbari, S. Leoni et al., Phys. Lett. B 855, 138851 (2024).
[3] J. Okołowicz, M. Płoszajczak and W. Nazarewicz, Phys. Rev. Lett. 124, 042502 (2020).
[4] J. Okołowicz, M. Płoszajczak and W. Nazarewicz, J. Phys. G.: Nucl. Part. Phys. 49, 10LT01 (2022).
[5] S. Capra, D. Mengoni, J.A. Dueñas et al., Nucl. Instr. Meth. A 935, 178-184 (2019).
[6] G. Corbari, M. Ciemała, S. Bottoni et al., submitted to Phys. Lett. B.

Isospin symmetry arises from the charge independence of nucleon–nucleon interactions, but it is broken by the Coulomb interaction. Although a small effect, its precise determination is essential for understanding isobaric analogue states and their role in β decay.
In self-conjugate N = Z nuclei, electromagnetic selection rules forbid electric dipole (E1) γ decay. Therefore, the observation of E1 strength provides a sensitive probe of isospin mixing. The giant dipole resonance (GDR), an E1 mode, is widely used to quantify this effect [1-3].
Following early measurements in $^{28}$Si and $^{32}$S [4-6], which indicated an increase of isospin mixing with mass number A, our Milano group carried out a systematic study in N = Z nuclei in the range A = 60–80 [1-3]. In particular, $^{80}$Zr and $^{60}$Zn were investigated at LNL-INFN using GARFIELD, AGATA and GALILEO arrays coupled to BaF$_2$ or LaBr$_3$:Ce detectors, allowing the extraction of isospin mixing and its temperature dependence.
As the most recent case within this program, we studied $^{72}$Kr at a nuclear temperature of ~1.3 MeV via GDR γ decay. Measurements were performed at the Bucharest Tandem Laboratory using the ELIGANT array [7] for the reactions $^{32}$S + $^{40}$Ca (I = 0) and $^{31}$P + $^{40}$Ca (reference, I ≠ 0).
Statistical-model analysis yields an isospin mixing parameter of (3.5 ± 0.8)%, confirming the predicted temperature dependence. By combining all results, we present a systematic study of isospin mixing as a function of mass and temperature. Finally, the extracted isospin-symmetry-breaking correction δ$_C$, relevant for superallowed Fermi β transitions, is consistent with β-decay data, theoretical predictions, and previous measurements [8].

References
[1] A. Corsi et al., “Measurement of isospin mixing at a finite temperature in $^{80}$Zr via giant dipole resonance decay,” Physical Rewiev C, vol. 84, p. 041304(R), 2011
[2] S. Ceruti et al., “Isospin mixing in $^{80}$Zr: From finite to zero temperature,” Physical Rewiev Letters, vol. 115, p. 222502, 2015.
[3] G. Gosta et al., “Probing isospin mixing with the giant dipole resonance in the $^{60}$Zn compound nucleus,” Physical Rewiev C, vol. 103, p. L041302, 2021.
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[7] P.-A. Söderström et al., “Eligant-Gn-ELI gamma above neutron threshold: The gamma-neutron setup,” Nuclear Inst. and Methods in Physics Research, A, vol. 1027, p. 16617, 2022.
[8] A. Giaz et al., “Probing the Isospin Mixing in the $^{72}$Kr Compound Nucleus via GDR γ Decay” Physics Letters B, 868 (2025) 139653.

The commissioning of a proton cyclotron for hadron therapy at the Cyclotron Centre Bronowice (CCB) of the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Krakow has enabled the use of proton beams for nuclear physics experiments. Among others, an experimental campaign was carried out aiming at study the γ decay from excited atomic states, such as giant and pygmy resonances.
The employed experimental method was based on coincidence measurement of scattered protons registered by the KRATTA [1] array and gamma rays emitted from the decay of excited nuclei measured using LaBr$_3$ detectors together with PARIS [3] phoswiches.

One of the main goals of the experiments was to study a very rare phenomenon – the decay of GQR (giant quadrupole resonance) via γ-ray emission to the ground state. Previously such phenomenon was observed only once, in 1980s [3]. In recent experiment we have confirmed the existence of the GQR gamma-decay and measured the branching ratio between GQR gamma decay to ground state and neutron emission for $^{208}$Pb [4]. Similar measurements were also performed for $^{120}$Sn.

During the talk the experimental method, the used equipment as well as the obtained results will be presented. In addition, the outlook for the continuation of such studies will be discussed.

References
[1] J. Łukasik et al., Nucl. Instrum. Methods Phys. Res., Sect. A709, 120 (2013);
[2] A. Maj et al., Acta Phys. Pol. B 40, 565 (2009);
[3] J.R. Beene, et al., Phys. Rev. C 39, 1307 (1989);
[4] B. Wasilewska et al., Phys. Rev. C 105, 014310 (2022).

The 4n system 8He, comprising several features of a 2n and 4n sub-system is interesting by its internal correlations leading to the possibility to study several aspects of clustering in light nuclei. 8He, in particular it’s coulomb breakup, studied in a recent experiment, will be presented and discussed. The relation to previously obtained information will be drawn and future prospects arising at the FAIR facility will be presented.

Many-body Green's function theory stands out among microscopic theories for its capability to encapsulate infromation on ground state properties, response and single particle spectroscopy within the same framework. Different aspects of the many-body correlations and dynamics of a given nucleus can then be investigated simultaneously with the same microscopic approach.

The first part of the talk will focus on ongoing work to extend self-consistent Green's function (SCGF) theory to describe pairing effects in the presence of collective excitations--the so called Gorkov-ADC(3) framework [1]--with recent applications to nuclear matter [2]. I will then cover exploitation of diagrammatic Monte Carlo methods [3] for devising first principle optical potentials [4].

The second part of the talk will cover recent results regarding the structure near the Ar and Ca isotopic chains. In particlar, I will further discuss the analysis of a recent GANIL experiment that provided evidence for a charge bubble in 46Ar and linked this to an atypical shell closure at Z=18 and N=28 [5].

[1] C. Barbieri, T. Duguet and V. Somà, Phys. rev. C 105, 044330 (2022).
[2] F. Marino, C. Barbieri, and G. Colò, arXiv:2601.03763 and Phys. Rev. C (2026) in print.
[3] S. Brolli, C. Barbieri and E. Vigezzi, Phys. Rev. Lett. 134, 182502 (2025).
[4] S. Brolli and C. Barbieri, arXiv:2605.30527 (2026).
[5] A. Idini, C. Barbieri and P. Navrátil, Phys. Rev. Lett. 123, 092501 (2019).
[6] D. Brugnara et al., arXiv:2506.23228.

A major goal of nuclear theory is to explain the structure and properties of atomic nuclei in an ab initio approach starting from nuclear forces fixed in free-space scattering. Apart from the two nucleon forces, the three-body forces are also important in describing systems from light nuclei to nuclear matter. However, an accurate and simultaneous ab initio prediction for both light nuclei and nuclear matter has been a long- standing challenge in nuclear physics, due to the significant uncertainties associated with the three-nucleon forces.

In a series of recent works, we have developed a deep-learning-based ab initio framework, FeynmanNet, which achieves high variational accuracy with polynomial scaling in the nucleon number. In particular, it demonstrates that both light nuclei and nuclear matter can be well described simultaneously in the relativistic ab initio calculations, even in the absence of three-nucleon forces, and a correlation between the properties of light nuclei and the nuclear saturation is revealed.

References:
[1] Y. L. Yang and P. W. Zhao, Phys. Lett. B 835, 137587 (2022).
[2] Y. L. Yang and P. W. Zhao, Phys. Rev. C 107, 034320 (2023).
[3] Y. L. Yang and P. W. Zhao, Phys. Rev. Lett. 134, 242502 (2025).
[4] Y. L. Yang and P. W. Zhao, Chin. Phys. Lett. 42, 051201 (2025).
[5] Y. L. Yang, E. Epelbaum, J. Meng, L. Meng, and P. W. Zhao, Phys. Rev. Lett. 135, 172502 (2025)

Understanding nuclear structure from fundamental interactions and equations, i.e., ab initio, is a foundational task of nuclear theory. It has long been a challenge to achieve a universal description of various exotic nuclear phenomena in a unified ab initio framework. This talk presents recent advancements using nuclear lattice effective field theory (LEFT) to bridge this gap.

We first explore the low-lying spectrum and geometric structures of $^{12}\text{C}$, where the $\alpha$-clustering reveal the "bent-arm" configuration of the enigmatic Hoyle state. We then extend our systematic study to the beryllium isotopic chain ($^{7}\text{Be}$ to $^{12}\text{Be}$), where LEFT successfully captures diverse phenomena including molecular-orbital and one-neutron halo. Finally, we discuss a parameter-free calculation of the $\alpha$-particle monopole transition form factor, showing excellent agreement with high-precision data from MAMI. These results demonstrate that LEFT provides a powerful, predictive framework for unifying our understanding of nuclear clustering, shell evolution, and few-body dynamics across the chart of nuclides.

Atomic nuclei are ideal probes to test fundamental symmetries. For instance, nuclei are used as targets to detect dark matter particles, and electric dipole moments of nuclei can help to unveil why there is more matter than antimatter in the universe.

Nuclear $\beta\beta$ decays also play a paramount role. If no neutrinos happen to be emitted in the decay, this would immediately imply that the neutrino and the antineutrino are the same particle, as proposed by Ettore Majorana in the early days of quantum field theory. Nonetheless, the rate of the Majorana $\beta\beta$ decays depend on nuclear matrix elements that need to be predicted by nuclear theory, as these decays have not been observed yet experimentally.

In this talk, I will present recent advancements on the calculation of the rates of Majorana $\beta\beta$ decays, with emphasis on the impact of the nuclear structure of the initial and final states of the transition. To conclude, I will also propose how nuclear structure experiments can help to constrain the values of the Majorana $\beta\beta$ decay rates.

We present a systematic study of bulk properties, low-energy spectra, and giant resonances of closed-shell nuclei within an ab-initio renormalized random-phase approximation (RRPA) framework [1,2].

For the first time, modern chiral interactions including explicit three-nucleon forces [3] are implemented consistently within the RRPA approach. The renormalization of the RPA equations removes instabilities associated with the quasiboson approximation, resulting in a stable and internally consistent description of binding energies, radii,
excitation spectra, and electromagnetic responses.

The achieved performance, together with the robustness of the method near shell closures across the nuclear chart, establishes RRPA with modern chiral interactions as a promising and complementary tool for ab initio nuclear structure studies.

[1] F. Knapp, R. Folprecht, G. De Gregorio, P. Veselý, N. Lo Iudice, EPJ Web Conf. 342 01013 (2025).
[2] R. Folprecht, F. Knapp, G. de Gregorio, R. Mancino, P. Veselý, and N. Lo Iudice, Phys. Rev. C 113, L041302 (2026).
[3] T. Miyagi, Eur. Phys. J. A 59, 150 (2023).

Recent experiments have shown that fission fragments carry intrinsic angular momentum with essentially no correlation between fragments, motivating new theoretical studies. Different microscopic models will be discussed to understand the generation of fragment spin in fission. These approaches, based on time-dependent density functional theory and a time-dependent collective Hamiltonian, investigate the origin of angular momentum during and after scission. By comparing projection techniques with simple estimates from the uncertainty principle, fragment spin is shown to emerge from the quantum uncertainty between orientation angle and angular momentum, together with the effects of fragment deformation.

Nuclear energy density functional (EDF) theory provides a unified framework for describing both static and dynamical properties of nuclei and extended nuclear matter. In particular, its time-dependent extension enables microscopic studies of non-equilibrium phenomena in strongly paired systems, such as those expected in the inner crust of neutron stars, where nuclei coexist with a superfluid neutron background. In this talk, I will present recent developments in time-dependent EDF approaches for nuclear superfluids, with emphasis on large-scale simulations of real-time dynamics [1]. I will discuss the motion of a quantized vortex interacting with a nuclear impurity embedded in superfluid neutron matter, highlighting the microscopic origin of vortex–nucleus forces. I will also introduce a dynamical scheme for extracting effective mass parameters of neutron-rich nuclei immersed in a superfluid medium, providing insight into collective inertial properties beyond static approaches [2]. These results establish a consistent microscopic picture of dynamical processes in neutron star crusts and provide new insights into the rotational dynamics of neutron stars, including mechanisms relevant to pulsar glitches.

[1] D. Pȩcak, A. Zdanowicz, N. Chamel, P. Magierski, G. Wlazłowski, Time-dependent nuclear energy-density functional theory toolkit for neutron star crust: Dynamics of a nucleus in a neutron superfluid, Phys. Rev. X 14, 041054 (2024)
[2] A. Zdanowicz, D. Pęcak, P. Magierski, G. Wlazłowski, Dynamical scheme for computing the mass parameter of a system in a medium, Phys. Rev. C 112, 045804 (2025)

The optical potential is a well-established and widely used tool to describe nucleon-nucleus scattering processes. Within this approach, it is possible to compute the scattering observables for elastic processes across a wide region of the nuclear landscape and extend its usage to inelastic scattering and other types of reactions.

Since phenomenological approaches lack predictive power, we strongly believe that a microscopic approach will be the preferred tool to make reliable predictions, in particular for upcoming experiments concerning exotic nuclei.

The Watson multiple scattering theory provides a successful framework to derive such an optical potential for intermediate energies.
In its simplest formulation, derived at the first order, the optical potential is obtained as the folding integral of the nucleon-nucleon scattering matrix and the target density, representing the two fundamental ingredients of the model. After many years of advances in theoretical nuclear physics, it is now possible to calculate these two quantities using the same nucleon-nucleon interaction that is the
only input of our calculations.
Results obtained within this framework will be presented for light- and medium-mass nuclei, adopting different ab initio approaches to calculate the densities, such as the No-Core Shell Model and Self-Consistent Green’s Function [1-7]. Novel extensions of the model, such as the calculation of nucleus-nucleus collisions [8] or inelastic transitions [9] will also be presented.

References

[1] M. Vorabbi, P. Finelli, C. Giusti, Phys. Rev. C93, 034619 (2016)
[2] M. Vorabbi, P. Finelli, C. Giusti, Phys. Rev. C96, 044001 (2017)
[3] M. Vorabbi, P. Finelli, C. Giusti, Phys. Rev. C98, 064602 (2018)
[4] M. Vorabbi, M. Gennari, P. Finelli, C. Giusti, P. Navratil, Phys. Rev. Lett. 124, 162501 (2020)
[5] M. Vorabbi, M. Gennari, P. Finelli, C. Giusti, P. Navratil, Phys. Rev. C103 024604 (2021)
[6] M. Vorabbi, M. Gennari, P. Finelli, C. Giusti, P. Navratil, Phys. Rev. C105 014621 (2022)
[7] M. Vorabbi ,C. Barbieri ,V. Somà ,P. Finelli , and C. Giusti, Phys.Rev. C109 (2024) 3, 034613
[8] M. Vorabbi, M. Gennari, P. Finelli, C. Giusti, P. Navratil, Phys. Rev. Lett. 135,172501 (2025)
[9] M. Vorabbi, M. Gennari, P. Finelli, C. Giusti, P. Navratil, submitted to Phys.Rev. C (2026)

The synthesis of superheavy elements is a major foundational scientific problem of joint interest to both the fields of physics and chemistry. Experimentally, fusion-evaporation reactions are commonly employed for the synthesis of superheavy nuclei, but thus far have only resulted in neutron-deficient superheavy nuclei.
The pursuit of the "island of stability" for superheavy nuclei thus requires novel reaction mechanisms. Multinucleon transfer (MNT) reactions provide a promising pathway for synthesizing neutron-rich heavy and superheavy nuclei, and have attracted extensive attention both experimentally and theoretically, becoming a major topic in nuclear physics. However, due to the complex mass and angle distributions of MNT reaction products, significant challenges exist in their collection and separation [1]. Therefore, the investigation of MNT reactions requires a close integration of experiment and theory.

Covariant density functional theory (CDFT), based on effective field theory and density functional concepts, has achieved great success in the microscopic, self-consistent, and unified description of nuclear structure properties. Its time-dependent extension, known as time-dependent covariant density functional theory (TD-CDFT), is a powerful microscopic tool for the study of nuclear reactions and decays, and has been successfully applied to fusion, fission, and quasifission phenomena. For the study of MNT reactions, since the product wave functions are not eigenstates of the particle number or angular momentum operators, the application of TD-CDFT to MNT requires the combination of particle number projection and angular momentum projection techniques.

In this work, the TD-CDFT approach incorporating particle number and angular momentum projection has been developed to investigate the mass and spin distributions of products in MNT reactions. By calculating the cross-sections for several reaction systems and comparing the results with experimental data, the reliability of the theoretical model in reproducing experimental observations is verified [2]. Furthermore, ternary quasifission in actinide collisions is explored, predicting a possible pathway for the synthesis of neutron-rich heavy nuclei [3]. Finally, the spin distribution and its correlations among the reaction products are analyzed, revealing that, as nucleon transfer increases, the spins of the products become larger and the distributions broader. This effect arises from the conversion of orbital angular momentum into intrinsic spin due to friction between the projectile and target nuclei. Entanglement Shanon entropy analysis of the product spins indicates weak correlations among fragments [4].

[1] Xiaohong Zhou, Zhiyuan Zhang, Zaiguo Gan, et al., Research program of superheavy elements and nuclides based on HIAF (in Chinese). Sci Sin-Phys Mech Astron 50, 112002 (2020).
[2] Dan Dan Zhang, Dario Vretenar, Tamara Nik\v si\' c, Peng Wei Zhao, and Jie Meng, Multinucleon transfer with time-dependent covariant density functional theory, Phys. Rev. C 109, 024614 (2024).
[3] Dan Dan Zhang, Bo Li, Dario Vretenar, Tamara Nik\v si\' c, Zheng Xue Ren, Peng Wei Zhao, and Jie Meng, Ternary quasifission in collisions of actinide nuclei, Phys. Rev. C 109, 024316 (2024).
[4] Dan Dan Zhang, Dario Vretenar, Tamara Nik\v si\' c, Peng Wei Zhao, and Jie Meng, Intrinsic spin distributions in multinucleon transfer reactions, Phys. Lett. B 869, 139828 (2025).

Atomic nuclei are complex many-body systems with a number of constituents ranging from very few to several hundred [1-2]. Among the difficult aspects, nuclei are self-bound systems that require treating a continuum of wave functions in Hilbert space. The nuclear strong interaction is poorly understood and highly non-perturbative, with the onset of multi-body interactions beyond the usual two-body interactions. Nuclear physics also faces the exponential growth of the Hilbert space as the number of constituents increases. For these reasons, the exact treatment of these systems on classical computers, starting from the interaction, is still restricted to a few percent of the nuclear chart.
Quantum technologies and associated quantum algorithms appear in this context as disruptive technologies that might surpass the current limitations in the coming years [3]. We have initiated a long-term project to explore the use of quantum computers in nuclear physics and related many-body problems. Inspired by strategies used in classical computing, several novel approaches have been proposed to obtain the ground or low-lying states in many-body systems. A significant effort has been made to use the symmetry-breaking/symmetry-restoration method [2,4,5]. Based on the use of projectors through phase estimation, quantum oracles, or classical shadow, the Quantum Variation After Variation was formulated. Several methods were proposed to access excited states, including the Quantum Krylov, Quantum equation of motion, or Quantum Generator Coordinate Method [6,7,8]. These methods will be highlighted, along with their applications to the nuclear physics many-body problem. Recent results on methods to describe ground and excited states for the proton-neutron pairing will be discussed [9,10], and Green’s function will be presented [11].

References:

[1] Quantum computing with and for many-body physics, Ayral, P. Besserve,
D. Lacroix and E. A. Ruiz Guzman, Eur. J. Phys. A. 59, 227 (2023), arXiv:2303.04850 [Review]

[2] Symmetry breaking/symmetry preserving circuits and symmetry restoration on quantum computers: A quantum many-body perspective, D. lacroix, E. A. Ruiz Guzman and P. Siwach, Eur. Phys. J. A 59, 3 (2023). arXiv:2208.11567 [Review]

[3] Quantum Computing for High-Energy Physics: State of the Art and Challenges. Summary of the QC4HEP Working Group, A. Di Meglio et al, PRX Quantum 5, 037001 (2024) , arxiv:2307.03236. [White paper]

[4] Restoring symmetries in quantum computing using Classical Shadows, Edgar Andres Ruiz Guzman, Denis Lacroix, Eur. J. Phys. A 60, 112 (2024). arXiv:2311.04571

[5] Restoring broken symmetries using quantum search oracles, E. A. Ruiz Guzman and D. Lacroix, Phys. Rev. C 107, 034310 (2023), arXiv:2210.11181

[6] Entanglement in selected Binary Tree States: Dicke/Total spin states, particle number projected BCS states, D. Lacroix, Phys. Rev. C 110, 034310 (2024), arxiv:2405.04665

[7] Neutron-proton pairing correlations described on quantum computers, Jing Zhang, Denis Lacroix and Yann Beaujeault-Taudière, submitted to Phys. Rev. C, arXiv:2408.17294

[8] Solving the Lipkin model using quantum computers with two qubits only with a hybrid quantum-classical technique based on the Generator Coordinate Method, Yann Beaujeault-Taudière and Denis Lacroix, Phys. Rev. C 109, 024327 (2024), arXiv:2312.04703

[9] Neutron-proton pairing correlations described on quantum computers, Jing Zhang, Denis Lacroix and Yann Beaujeault-Taudière, submitted to Phys. Rev. C, arXiv:2408.17294

[10] Excited states from ADAPT-VQE convergence path in many-body broblems: application to nuclear pairing problem and H_4 molecule dissociation, Jing Zhang, and Denis Lacroix, Phys. Lett. B869, 139841 (2025), arXiv:2506.22275

[11] Quantum simulations of Green's functions for small superfluid systems, Samuel Aychet-Claisse, Denis Lacroix, Vittorio Somà, Jing Zhang, Phys. Rev. C 113, 044324 (2026), arXiv:2509.02272

Quantum computing offers a fundamentally new paradigm for simulating the real-time dynamics of quantum many-body systems, overcoming the exponential scaling limitations of classical approaches. By encoding quantum states directly into qubits and leveraging entanglement as a computational resource, quantum algorithms can efficiently capture the complex correlations that govern nuclear reactions. This capability opens the door to accurate, first-principles simulations of reaction mechanisms, including strongly interacting and highly non-equilibrium regimes that remain intractable today. As quantum hardware and algorithms mature, they have the potential to transform our understanding of nuclear dynamics, enabling predictive modeling with unprecedented fidelity.
Realizing this potential requires a sequence of algorithmic components, including efficient preparation of the initial nuclear wavefunction [1,2], controlled time evolution under the relevant Hamiltonian, and the extraction of physical observables through carefully designed measurement protocols. Each of these stages presents distinct challenges, from encoding correlated initial states to mitigating errors during long-time evolution and reconstructing scattering information from quantum measurements. To accurately describe continuum dynamics and reaction products, it is advantageous to employ first-quantized representations, which scale favorably with system size and provide a natural framework for asymptotic state represenation, while requiring explicit enforcement of fermionic antisymmetry [3,4].
In this talk, I present a unified framework for quantum simulation of nuclear reactions, spanning both state preparation and observable extraction. I discuss projection-based techniques for preparing nuclear states with well-defined quantum numbers and correlations, viewing state preparation itself as a form of time evolution [1,2]. Building on these methods, I introduce an approach in which scattering clusters are initialized as wave packets and evolved to asymptotic separation within a finite computational volume [5]. By computing appropriate overlap functions, scattering matrix elements at fixed energy can be obtained via Fourier transform. This strategy requires only unitary time evolution beyond state preparation, making it well suited for implementation on quantum hardware.
I will show how this framework enables the ab initio calculation of differential and total cross sections for two-cluster reactions, including inelastic processes where clusters transition between internal eigenstates [5]. Numerical examples illustrating these capabilities will be presented.
Acknowledgment: LA-UR-26-22966. This work was carried out under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at Los Alamos National Laboratory under Contract No. 89233218CNA000001.

References:
[1] I. Stetcu, A. Baroni, and J. Carlson, Phys. Rev. C 105 (2022) 064308
[2] E. Rule, I. Stetcu, and J. Carlson, Phys. Rev. C 110 (2024) 064003
[3] E. Rule et al., Quantum 10 (2026) 2056
[4] I. Stetcu, arXiv:2512.16138
[5] E. Rule and I. Stetcu, arXiv:2603.26881

An accurate description of many-body dynamics in nuclear physics is a major challenge for classical simulation techniques. Hamiltonian simulation on digital quantum computers offer the possibility of reducing the computational cost when tackling these problems. In this talk, I will discuss recent advances in the simulation of both nuclear and neutrino systems using quantum computers and show some results obtained with current generation devices.

Nuclear many-body calculations on classical computers typically involve Monte Carlo simulations. These suffer from the fermionic sign problem where the signal-to-noise ratio diminishes as the system size grows. Moreover, these simulations are performed in Euclidean which complicates calculations of real-time dynamics from such simulations. Quantum computation avoids these issues by unitary evolution in real-time. In this talk, I present several algorithms to calculate elastic and inelastic reaction matrix elements on quantum computers. Results for two-particle phase shifts, E1 transition matrix elements and mass gap calculations are presented.

Quantum computers have the potential to efficiently tackle problems that grow exponentially in complexity on classical computers. In the context of simulating physical systems, they may help reduce the problems related to the rapid expansion of Hilbert space with increasing particle number and handle highly entangled states more effectively.

In this contribution, we explore prospects for using quantum computers for nuclear structure problems. We present some applications of a low-depth variational quantum algorithm [1] to solve problems in nuclear structure, including the preparation of ground and excited states within the nuclear shell model approach. Here, we implement a new qubit-mapping strategy for the Variational Quantum Eigensolver (VQE) in nuclear shell-model calculations, in which each Slater determinant (SD) is encoded into a single qubit state, rather than mapping qubits to individual single-particle states.

References:
[1] C. Sarma, and P. D. Stevenson, Discov. Quantum Sci. 2, 6 (2026).

At the VITO beamline at ISOLDE, we use optical pumping to polarise nuclear spins of beams of different short-lived nuclei [1]. We then use the resulting anisotropic emission of beta radiation in a variety of fields, from nuclear structure, via material science, all the way to biology.
Recently, we have used $^{47,49,51}$K for a proof-of-principle experiment in decay spectroscopy of spin-polarized beams, in which we studied angular correlations between asymmetrically emitted beta particles and gamma-radiation or neutrons [2]. The aim is to use the measured beta-decay asymmetry factors to determine spins and parities of excited states in neutron-rich nuclei, especially beta-delayed neutron emitters relevant for the r process nucleosynthesis.
Furthermore, we use the spin-polarised beams for ultra-sensitive nuclear magnetic resonance detected via beta-decay asymmetry ($\beta$-NMR). By using liquid samples we have narrowed the linewidth of $\beta$-NMR resonances by two orders of magnitude, allowing to achieve ppm levels in the accuracy of magnetic moments of short-lived isotopes [3]. We have now combined this approach with nuclear DFT and atomic calculations to determine the so-called hyperfine anomaly in $^{47}$K [4], paving the way for studies of the composition and distribution of nuclear magnetisation in different short-lived nuclei [5].
This contribution will present the VITO experimental setups, followed by the results of the above-mentioned proof-of-principle studies, concluding with a layout of an rf-laser spectroscopy end station for precise hyperfine-anomaly studies.

1. M. Kowalska et al., J. Phys. G: Nucl. Part. Phys. 44 (2021) 084005
2. M. Piersa-Silkowska et al., CERN-INTC-2023-026/ INTC-P-662 (2023), and https://ep-news.web.cern.ch/content/isoldes-new-beta-decay-station-unlocks-advanced-decay-spectroscopy-experiments-laser (2025)
3. R. Harding et al., Phys. Rev. X 10 (2020) 041061, J. Croese et al, NIMB 1020 (2021), 165862, M. Jankowski et al JINST 21 (2026) P01003
4. M.L. Bissell et al, submitted, https://arxiv.org/abs/2603.20090
5. M.L. Bissell et al, CERN-INTC-2023-014 / INTC-P-655 (2023)

Charge-changing reactions (CCRs) at intermediate energies are an experimentally simple yet valuable tool for exploring the complex reaction mechanisms and exotic structures of rare isotopes.
Based on years of experimental studies at RIBLL2/HIRFL and FRS/GSI, our collaboration has investigated CCRs of more than 60 p-sd shell nuclei on various targets at approximately 300 and 900 MeV/nucleon.
Benefiting from this extensive and systematic dataset, we have demonstrated the indispensable role of charge-particle evaporation after neutron removals in CCR. We found an empirical yet robust method to infer the charge radii of isotopes of p-shell nuclei and suggest a heavy isotope target as the optimal choice. I will present some selected new results from our CCR studies and the perspective on using the Heavy-ion Accelerator Facility (HIAF).

Refs:
[1] J.C. Zhang et al., Physical Review X 15(2025)031004
[2] X.D. Xu et al., Science Bulletin 70(2025)1026.
[3] J. W. Zhao et al., Physics Letters B 858 (2024) 139082.
[4] J.C. Zhang et al., Science Bulletin 69 (2024) 1647.
[5] G.S. Li et al., Physics Letters B 859 (2024) 139143
[6] J.W. Zhao et al., Physics Letters B 847 (2023) 138269.
[7] C.J. Wang et al., Chinese Physics C 47 (2023) 084001.

The Gamma-Ray Energy Tracking Array (GRETA) is 4pi detector designed to study a broad science program in nuclear structure over a wide range of beam energies and velocities from Coulomb barrier to 100’s MeV/A. It combines highly segmented HPGe crystals with advanced digital electronics and signal processing to identify individual gamma-ray interaction points within the crystals to simultaneously achieve high energy resolution, high efficiency, and good background rejection (peak-to-total).

The GRETA Project started in 2017, following nearly a decade of successful science with the predecessor GRETINA array and completed construction and initial commissioning of all technical systems (mechanical, electronics and computing) with a subset of Quad Detector modules at LBNL in the summer of 2025. It is currently being installed at the Facility for Rare Isotope Beams (FRIB), with first science measurements expected early 2027. I will review the GRETA project, both science and technical as well performance, and the progression toward anticipated first science at FRIB.

The AGATA γ-ray tracking array represents the state of the art in in-beam gamma-ray spectroscopy, exploiting the high segmentation of High Purity Germanium detectors to achieve position sensitivity and gamma-ray tracking via pulse-shape analysis [1,2]. Installed in April 2022 at the Tandem–ALPI–PIAVE accelerator complex of INFN Laboratori Nazionali di Legnaro, AGATA has operated with beam energies spanning 7–8 MeV/u for the heaviest ions up to 20–25 MeV/u for the lightest.
Routinely coupled to the PRISMA heavy-ion magnetic spectrometer, and complemented by silicon detector arrays for light charged particles, AGATA has addressed a broad physics programme: shell evolution, quadrupole and octupole collectivity, astrophysically motivated measurements, and systematic Coulomb-excitation studies.
This presentation will provide an overview of the performance of AGATA and show selected recent achievements such as the double double octupole phonon in 96Zr and lifetime measurements in the heavy Os-Pt region near N=126.

References
[1] A. Akkoyun et al., Nucl. Instrum. Methods A 668, 26 (2012).
[2] J. J. Valiente-Dobón et al., Nucl. Instrum. Methods A 1049, 168040 (2023).

Light neutron-rich carbon isotopes provide a unique testing ground for the evolution of shell structure and halo phenomena. Specifically, we studied the single-neutron pickup $^{16}\mathrm{C}(p,d)^{15}\mathrm{C}$ and $^{16}\mathrm{C}(d,t)^{15}\mathrm{C}$, and the two-neutron pickup $^{16}\mathrm{C}(p,t)^{14}\mathrm{C}$. These complementary probes offer high sensitivity to both single-particle and pairing correlations, serving as critical benchmarks for theoretical models of transfer reactions with exotic beams.

The pickup reaction allowed us to study particle-hole configurations in $^{15}\mathrm{C}$ produced by the removal of neutrons from the $1p_{1/2}$ and $1p_{3/2}$ orbitals . The comparison of these results with different phenomenological interactions shows the sensitivity to the size of the N =8 gap and helps to constrain them [1]. In particular, $^{15}\mathrm{C}$ is a well-known one-neutron halo nucleus, with the valence neutron weakly bound ($S_n \approx 1.2$ MeV) in a $2s_{1/2}$ orbital. Its first excited state at 0.74 MeV has a dominant $1d_{5/2}$ configuration, with the transition expected to involve weak core polarization due to the inert ¹⁴C core [2]. Understanding how the halo in $^{15}\mathrm{C}$ impacts core polarization is directly relevant for understanding the quadrupole moments of $^{16}\mathrm{C}$ [2].

The experiment was performed in 2023 at the Argonne Tandem Linac Accelerator System [3] (ATLAS) using the Active Target Time Projection Chamber (AT-TPC) [4] and HELIOS solenoidal spectrometer [5,6] to study transfer reactions that selectively populate single-particle states, from which spectroscopic factors are extracted.

This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contracts No. DE-AC02-06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility. This work has received financial support from the Xunta de Galicia (CIGUS Network of Research Centres) and the European Union.

References:
[1] J. Lois-Fuentes et al., EPJ Web Conf. (2023).
[2] J. Chen et al., Physical Review C 106.6 (2022): 064312.
[3] C. Hoffman, T. Tang, M. Avila, Y. Ayyad, K. Brown, J. Chen, K. Chipps, H. Jayatissa, B. Kay, C. Müller-Gatermann, H. Ong, J. Song, and G. Wilson, Nucl. Instr. Meth. Phys. Res. Sect. A 1032, 166612 (2022).
[4] J. Bradt, D. Bazin, F. Abu-Nimeh, T. Ahn, Y. Ayyad, S. Beceiro-Novo, L. Carpenter et al.  Nucl. Instr. Meth. Phys. Res. Sect. A  875 (2017): 65-79.
[5] A. Wuosmaa, J. Schiffer, B. Back, C. Lister, and K. Rehm, Nucl. Instr. Meth. Phys. Res. Sect. A 580, 1290 (2007).
[6] J. Lighthall, B. Back, S. Baker, S. Freeman, H. Lee, B. Kay, S. Marley, K. Rehm, J. Rohrer, J. Schiffer, D. Shetty, A. Vann, J. Winkelbauer, and A. Wuosmaa, Nucl. Instr. Meth. Phys. Res. Sec. A 622, 97 (2010).

In nuclear structure studies, the nucleon-nucleon correlations are recognised as crucial in determining the low-energy spectra and ground-state properties of nuclei. Heavy ion reactions are considered a valuable tool for investigating such correlations, since they enable the transfer of multiple nucleon pairs, both neutrons and protons, between the interacting nuclei [1-6].
We will present preliminary results of the analysis of data collected in an experiment conducted at LNL using the PRISMA + AGATA set-up, aimed at probing nucleon-nucleon correlations in the $^{48}$Ca + $^{208}$Pb, measuring the transfer probabilities for multi-neutron and multi-proton transfer channels at energies close to and below the Coulomb barrier.
The experiment was carried out in inverse kinematics, using a $^{208}$Pb beam directed at a $^{48}$Ca target, employing the superconducting PIAVE-ALPI accelerator complex.
The experimental setup consists of the PRISMA magnetic spectrometer [7], which was used to identify the light reaction products with high charge and mass resolution, enabling clear separation of multiple transfer channels;
and the AGATA $\gamma$-spectrometer [8], which allowed us to identify the gamma-transitions for each transfer channel. This will provide crucial information about the populated excited states and enable the extraction of both the intensities of these excited states and, using the information measured with PRISMA, the intensities of the ground-state populations.
In this selected system, both neutron and proton stripping and pick-up processes are open, offering a unique opportunity to investigate nucleon-nucleon correlations across a complete set of transfer channels within a single experiment. These preliminary results will help to better understand the relative importance of single-nucleon transfer and more complex processes involving correlated nucleon pairs, as well as the role of correlations in the dynamics of the collision. The present work is particularly timely in view of forthcoming experiments with radioactive beams in both proton-rich and neutron-rich regions, where a wealth of interesting new effects is predicted.

[1] R. A. Broglia and A. Winther, Heavy Ion Reactions (Addison-Wesley, Redwood City, CA, 1991).
[2] R. A. Broglia and V. Zelevinsky, Fifty Years of Nuclear BCS—Pairing in Finite Systems (World Scientific, Singapore,2013).
[3] D. Montanari et al., Phys. Rev. Lett. 113 (2014) 052501.
[4] D. Montanari et al., Phys. Rev. C 93 (2016) 054623.
[5] L. Corradi et al., Phys. Lett. B 834 (2022) 137477.
[6] S. Szilner, et al., Phys. Rev. Lett. 133 (2024) 202501.
[7] A. M. Stefanini, et al., Nucl. Phys. A701, 217c (2002).
[8] J.J. Valiente-Dobón et al., Nuc. Instr. Meth. A1049, 168040 (2023)

In the past few years, spectroscopy of radioactive molecules has been performed at ISOLDE (CERN) using the Collinear Resonance Ionization Spectroscopy (CRIS) experiment [1]. Given their structure and chemical properties, radioactive molecules are promising candidates for studies in different fields [2], including for more efficient extraction of refractory elements from ISOLDE targets [3].

Many reference electric quadrupole moments (EQM) of stable isotopes [4] have been extracted from measurements of the coupling constant of isotopes in diatomic molecules, e.g., KF (for 39,41K), HCl (for 35,37Cl), and HI (for 127I) [5,6,7], in combination with accurate calculations of the electric field gradient in the molecule. For some of these elements, the electric-field gradient is too small in atomic systems, or the element is not accessible for laser spectroscopy in its atomic form; thus, molecular spectroscopy is the only option for studying the quadrupole moments of their radioactive isotopes.

Following the successful high-resolution studies of 225,226RaF [8,9], the CRIS experiment at ISOLDE performed the first hyperfine-resolved resonance ionization spectroscopy of 223RaF, yielding the first measurement of the EQM in a short-lived radioactive molecule (t1/2 = 11.4 days) for 223Ra (I = 3/2). Additionally, the change in charge radii of 223,225,226Ra have been extracted from spectroscopy of RaF molecules with a precision comparable to atomic studies [10,11]. Finally, the magnetic dipole moment and finite magnetization contribution of 223,225RaF were extracted in a nuclear model-independent way.

This contribution will focus on the measured nuclear moments of 223RaF and compare them with atomic and ionic measurements reported in the literature. Our measurement, in combination with state-of-the-art relativistic coupled-cluster calculations of the electric field gradient in the molecule [12,13,14], provides an accurate and precise value for the 223Ra quadrupole moment. Thus, serving as a reference for the extraction of quadrupole moments of other isotopes. This work also demonstrates how molecular laser spectroscopy could offer a new pathway for extracting unknown nuclear moments of radioactive isotopes, not accessible in atomic form, using suitable radioactive molecules [15].

[1] Garcia Ruiz, R.F., et al. "Spectroscopy of short-lived radioactive molecules." Nature 581.7809 (2020): 396-400. https://doi.org/10.1038/s41586-020-2299-4
[2] Opportunities for Fundamental Physics Research with Radioactive Molecules, Rep Prog Phys. 2024 Jul 12;87(8). https://doi.org/10.1088/1361-6633/ad1e39
[3] Au, Mia. Production of actinide atomic and molecular ion beams at CERN-ISOLDE. No. CERN-THESIS-2023-228. 2023.
[4] Pyykkö, P. (2018). Year-2017 nuclear quadrupole moments. Molecular Physics, 116(10), 1328-1338.
[5] Kello, Vladimir. "Determination of the quadrupole moment of the halogen nuclei (Cl, Br, I) from molecular data." Molecular Physics 89.1 (1996): 127-137. https://doi.org/10.1080/002689796174047
[6] Kellö, Vladimir, and Andrzej J. Sadlej. "The quadrupole moment of the 39K and 41K nuclei from microwave data for KF and KCl." Chemical physics letters 292.4-6 (1998): 403-410. https://doi.org/10.1016/S0009-2614(98)00680-0
[7] Bieroń, Jacek, et al. "Nuclear quadrupole moments of bromine and iodine from combined atomic and molecular data." Physical Review A 64.5 (2001): 052507. https://doi.org/10.1103/PhysRevA.64.052507
[8] Wilkins, S. G., Udrescu, S. M., Athanasakis-Kaklamanakis, M., Garcia Ruiz, R. F., Au, M., Belošević, I., ... & Zülch, C. (2025). Observation of the distribution of nuclear magnetization in a molecule. Science, 390(6771), 386-389. https://doi.org/10.1126/science.adm7717
[9] S.-M. Udrescu, et al., Precision spectroscopy and laser-cooling scheme of a radium-containing molecule”, Nature Physics (2024) online January 9, https://doi.org/10.1038/s41567-023-02296-w
[10] Wansbeek, L. W., Schlesser, S., Sahoo, B. K., Dieperink, A. E. L., Onderwater, C. J. G., & Timmermans, R. G. E. (2012). Charge radii of radium isotopes. Physical Review C—Nuclear Physics, 86(1), 015503. https://doi.org/10.1103/PhysRevC.86.015503
[11] Lynch, K. M., Wilkins, S. G., Billowes, J., Binnersley, C. L., Bissell, M. L., Chrysalidis, K., ... & Yang, X. F. (2018). Laser-spectroscopy studies of the nuclear structure of neutron-rich radium. Physical Review C, 97(2), 024309. https://doi.org/10.1103/PhysRevC.97.024309
[12] Kudashov, A. D., Petrov, A. N., Skripnikov, L. V., Mosyagin, N. S., Isaev, T. A., Berger, R., & Titov, A. V. (2014). Ab initio study of radium monofluoride, RaF, as a candidate to search for P-and T, P-violation effects. Phys. Rev. A 90, 052513. https://doi.org/10.1103/PhysRevA.90.052513
[13] Petrov, A. N., & Skripnikov, L. V. (2020). Energy levels of radium monofluoride RaF in external electric and magnetic fields to search for P-and T, P-violation effects. Physical Review A, 102(6), 062801. https://doi.org/10.1103/PhysRevA.102.062801
[14] Skripnikov, L. V. (2020). Nuclear magnetization distribution effect in molecules: Ra+ and RaF hyperfine structure. The Journal of Chemical Physics, 153(11). https://doi.org/10.1063/5.0024103.
[15] Dognon, Jean-Pierre, and Pekka Pyykkö. "Determining nuclear quadrupole moments of Bi and Sb from molecular data." Physical Chemistry Chemical Physics 25.4 (2023): 2758-2761. https://doi.org/10.1039/D2CP04747K

Changes in the nuclear shell closures approaching the neutron drip line are among the key topics in contemporary nuclear structure research. Although the bound excited states of neutron-rich isotopes have been extensively investigated, information on the unbound states remains rather scarce. Neutron-unbound states in $^{50}$Ar and $^{52}$Ar were studied via the (p,2p) reaction using invariant-mass spectroscopy. Narrow resonances near the neutron separation energy were observed and compared with theoretical predictions, enabling tentative spin-parity assignments. The agreement between the predicted and observed level structures supports the persistence of the $N$=32 and $N$=34 shell gaps in neutron-rich argon isotopes.

The unbound nucleus $^{13}$Be is crucial for understanding the formation of the two-neutron halo nucleus $^{14}$Be. In particular, its resonance structure provides key insight into the $^{12}$Be–n interaction entering three-body descriptions of $^{14}$Be. The relative ordering of the lowest-lying $1/2^+$ and $1/2^-$ states remains an open question. Notably, the $1/2^-$ state extracted from the breakup of $^{14}$Be appears at an unexpectedly low energy compared to its isotone $^{15}$C ($^{14}$C+n).

To address these issues, we employ a two-neutron transfer reaction in inverse kinematics, using a $^{11}$Be radioactive beam at 5.4 MeV/u impinging on a state-of-the-art solid $^{3}$H target. This approach provides selective population of low-angular-momentum continuum configurations and enables the study of unbound states through the reconstruction of their decay products. The experiment was performed at the ISOLDE facility in the Scattering Experimental Chamber (SEC).

We present the experimental setup together with first results obtained with the tritium target. The data show clear sensitivity to continuum structures in $^{13}$Be via the (t,p) channel, reconstructed from the detected reaction products. The ongoing analysis suggests a connection between $^{13}$Be resonances and excited states in $^{12}$Be. These findings provide new constraints on the $^{12}$Be–n interaction and contribute to clarifying the structure of $^{13}$Be and its role in the formation of the halo nucleus $^{14}$Be. Preliminary results obtained with a deuterated target, where resonances in $^{11}$Be and $^{12}$Be are also populated, will be presented.

Quasielastic (QE) scattering in the vicinity of the Coulomb barrier serves as a highly sensitive probe of reaction dynamics in heavy-ion collisions. Within the coupled-channels (CC) framework, the interplay between relative motion and intrinsic nuclear excitations leads to a distribution of effective barriers, commonly referred to as barrier distributions. These distributions encode valuable information about nuclear structure and reaction mechanisms and can typically be extracted from QE measurements [1,2]. However, observed deviations from standard CC predictions suggest that additional weakly coupled channels such as nucleon transfer and non-collective excitations may play a significant role in shaping the measured barrier structure [2].

Experimental studies have shown that QE barrier distributions $D_{qe}$ for several systems are smoother than predicted by standard CC calculations [3,4,5,6,7]. This behavior has been observed in reactions involving $^{20}$Ne with $^{92}$Zr [3], $^{61}$Ni [4], and $^{94,95}$Mo [6], and $^{24}$Mg with $^{92}$Zr [5]. It is interpreted as a consequence of dissipative dynamics arising from coupling to a large number of weak non-collective states. Although individually weak, these couplings collectively redistribute kinetic energy into intrinsic degrees of freedom, resulting in a damping of the barrier distribution structure. To describe such effects, the coupled-channels approach extended with random matrix theory (CCRMT) has been developed, incorporating statistical couplings to single-particle excitations [8]. These results have motivated further investigations of this dissipation mechanism using different strongly deformed projectiles and target systems with varying single-particle level densities.

In this context, quasielastic scattering measurements for the $^{24}$Mg + $^{92,94,95}$Mo systems were performed at the China Institute of Atomic Energy (CIAE), Beijing. The experiment was carried out at the HI-13 tandem accelerator, which delivered a $^{24}$Mg beam with an average current of approximately 50 enA over an energy range of 71–93 MeV in 1 MeV increments. Enriched self-supporting targets of $^{92}$Mo (99.93%), $^{94}$Mo (98.97%), and $^{95}$Mo (95.40%), each with a thickness of about 100 $\mu$g/cm$^{2}$, were employed. QE events were recorded using an array of silicon detectors arranged in five concentric rings spanning backward angles of 139$^\circ$ to 170$^\circ$, supplemented by forward-angle detectors positioned at 30$^\circ$. This geometry ensured extensive angular coverage, enabling reliable extraction of quasielastic barrier distributions. An increase in single-particle level density from $^{92}$Mo to $^{95}$Mo is anticipated to strengthen dissipative effects, resulting in a progressive smoothing of the barrier distributions [6]. The analysis of the collected data is currently in progress and preliminary results will be presented during the conference.

REFERENCES
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The delicate balance between like-nucleon (proton-proton and neutron-neutron, pp and nn and proton–neutron pn pairing correlations plays a crucial role in shaping the structure, stability, and collective behavior of atomic nuclei. Proton--neutron interactions are particularly strong when both nucleons occupy the same orbitals, owing to the large overlap of their spatial wave functions, having a mayor a major impact on nuclei with $N\!\approx\!Z$. Although reduced in neutron-rich systems, these correlations can be microscopically enhanced in regions close to doubly magic nuclei

High-spin nuclear states provide a sensitive probe $pn$ interaction . At high angular momentum, the Coriolis force breaks nucleon pairs, promoting proton and neutron alignment. Signatures of such strong $pn$ interaction are isomeric $\beta$-decaying states in $N = Z$ nuclei that arise from fully aligned configurations of a proton pair and a neutron pair, such as the 12$^+$ ($\nu 0f_{7/2}^{-2}\times\pi0f_{7/2}^{-2}$) state in $^{52}$Fe~ and the 16$^+$ ($\nu0h_{9/2}^{-2}\times\pi0g_{9/2}^{-2}$) isomer in $^{96}$Cd.

In this contribution, we present the results of a high-statistics $\beta$-decay experiment conducted at the ISOLDE facility at CERN, utilizing pure Cd beams. Strong evidence for a $\beta$-decaying high-spin isomer has been identified in $^{128}$Cd, the two-neutron–two-proton hole nucleus relative to doubly magic $^{132}$Sn. Based on the experimental information and the comparison to calculations, the state is assigned as the so-far unobserved $18^+$ spin-gap isomer in $^{128}$Cd arising from the $\nu(0h_{11/2})^{-2}\pi(0g_{9/2})^{-2}$. An interpretation of the $^{128}$Cd isomeric state will be provided within the framework of symmetry-conserving configuration-mixing calculations as well as shell-model calculations.

Nuclei at and beyond 78Ni were studied by means of the RIKEN BigRIPS facility and BRIKEN 3He-based beta-delayed neutron array and Ge clovers [1]. The search for the 3s1/2 neutron orbital down-sloping towards 2d5/2 neutron 81Zn ground state was among the goals. Such 3s1/2 state may trigger halo-like structure in even-Z, odd-N neutron-rich isotopes beyond 78Ni. This halo-like state would eventually originate from loosely bound s-neutron creating an isomeric state at low energy. The beta-delayed neutron decay of 82Cu most likely populates such state in N=51 81Zn, and ultimately the beta-delayed neutron decay of 80Co can populate 3s1/2 state in 79Ni. These s-states would decay to the respective d-ground states with gamma and/or conversion electron emission. The nuclei 82Cu and 80Co were produced and identified in our experiment [1]. I'll discuss the search for N=51 81mZn including recent Isolde attempts.

Supported through the DOE Office of Science grant DOE-AC05-00OR22725

[1] Y. Shimizu, K. Rykaczewski et al. for BRIKEN collaboration “Exploration of neutron-rich isotopes around N = 50 via the in-flight fission of a 345-MeV/nucleon 238U beam”, Progress of Theoretical and Experimental Physics, 033D06, 2026.

We present recent results obtained in the $^{22}$Ne + $^{238}$U and $^{26}$Mg + $^{238}$U multi-nucleon transfer experiments performed within the current AGATA campaign at Laboratori Nazionali di Legnaro [1-3], aiming to explore the structural evolution of light nuclei towards the $N=20$ Island of Inversion [4]. Specifically, we focus on studying the evolution of quadrupole collectivity in even-even Ne and Mg isotopes, and on tracking negative-parity states from the fp shell in even-odd nuclei, locating excited intruder configurations toward the $N=20$ shell closure. The coupling between the AGATA $\gamma$ array and the PRISMA magnetic spectrometer allowed us to detect ion-$\gamma$ coincidences and to extract sub-picosecond lifetimes of excited states via the DSAM technique. In this work, level and decay schemes of $^{23-26}$Ne were extended and further characterized by $\gamma$-ray angular distributions. Preliminary lifetime measurements will also be discussed along with state-of-the-art calculations of quadrupole strengths, including very recent ab initio predictions [5-9].

[1] J. J. Valiente-Dob\'on et al., Nucl. Inst. Meth. in Phys. A 1069 (2023) 168040.
[2] S. Akkoyun et al., Nucl. Inst. Meth. in Phys. A 668 (2012) 26-58.
[3] A. M. Stefanini et al., Nucl. Phys. A 701 (2002) 217c-221c.
[4] K. Wimmer et al., Phys. Rev. Lett. 105 (2010) 252501.
[5] T. Otsuka et al., Phys. Rev. C 105 (2022) 014319.
[6] P. Marevi\'c et al., Phys. Rev. C 97 (2018) 024334.
[7] M. Frosini et al., Eur. Phys. J. A 58 (2022) 64.
[8] Z. H. Sun et al., Phys. Rev. C 111 (2025) 044304.
[9] Z. H. Sun et al., Phys. Rev. X 15 (2025) 011028.

The region near the $Z=28$ and $N=28$ shell closures provides a crucial testing ground for nuclear structure models. In particular, the neutron-deficient cobalt isotopic chain ($Z=27$) offers insights into the robustness of these magic numbers. At the $N=Z$ line, studies of the self-conjugate nucleus $^{54}$Co ($N=Z=27$) and its isomer provide essential information to investigate proton-neutron pairing correlations. Theoretical models predict a significant change in the mean-square charge radius for the ground state of self-conjugate nuclei compared to the isomeric state. While experiments on $^{38}$K, $^{42}$Sc, and $^{50}$Mn confirm this general trend, current models still underestimate the actual size of the effect, which highlights the need for new experimental data [1]. Additionally, precise nuclear charge radii for the superallowed $\beta$-emitter $^{54}$Co can be used to reduce uncertainties in $\mathcal{F}t$ value calculations, contributing to tests of the Standard Model and the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix [2].

To resolve this lack of experimental data, high-resolution collinear laser spectroscopy on neutron-deficient Co isotopes was performed at the IGISOL facility, University of Jyväskylä, Finland. This experimental approach allows the determination of ground- and isomeric nuclear properties by measuring the isotope shift and hyperfine structure of electronic transitions [3]. These measurements will improve our understanding of structural evolution across the $N=28$ shell closure, ultimately paving the way towards future campaigns targeting the proton emitter $^{53}$Co. This contribution provides an overview of these measurements, focusing on the extracted magnetic moments and isotope shifts. Finally, the first empirical estimates of the mean-square charge radii, obtained by comparing the cobalt data to regional systematic trends, will be presented.

References
[1] Á. Koszorús et al., "Proton-neutron pairing correlations in the self-conjugate nucleus $^{42}$Sc," Physics Letters B, 819, 136439 (2021).
[2] J. C. Hardy and I. S. Towner, "Superallowed $0^+ \rightarrow 0^+$ nuclear $\beta$ decays: 2014 critical survey, with precise results for $V_{ud}$ and CKM unitarity," Phys. Rev. C, 91, 025501 (2015).
[3] Á. Koszorús et al., "Nuclear structure studies by collinear laser spectroscopy," The European Physical Journal A, 60(1), 20 (2024).

In recent years, neutron-rich titanium isotopes have been within the interests of nuclear physicists for several reasons. In particular 58Ti in the context of the 64Cr Island of Inversion and 56Ti in connection with the new N = 32,34 magic numbers observed in the Ca isotopic chain.

The boundaries of the 64Cr island of inversion are still not completely established and with the most neutron-rich Ti isotopes we're approaching them. While 59Ti and 61Ti have been confirmed to have a significant component of g9/2 and d5/2 orbitals in the ground state, the ground-state configuration in 58Ti still remains unknown and so, its place within the IoI.
The spectroscopic observables of E(2+) and B(E2) for the next even-even nucleus in the titanium isotopic chain - 56Ti with 34 neutrons - have been measured in the past. While the E(2+) value supports the hypothesis that the N=34 magic number vanishes for Ti isotopes, a more precise measurement of the B(E2) value in 56Ti is required to draw further conclusions.
To address the discussed issues, an in-flight Coulomb-excitation experiment was performed at RIKEN.The combination of high intensity beams produced by the BigRIPS fragment separator and the high resolution gamma-ray spectroscopy setup HiCARI allowed for the simultaneous determination of B(E2) values from excitation cross sections as well as lifetime measurements.
In this talk, I will present the preliminary experimental results. A measurement of the B(E2) value for 58Ti and its comparison with theoretical calculations will determine whether it belongs to the IoI. An analogous measurement for 56Ti will tell us more about collectivity in this isotope and persistence of the N=34 magic number.

The region of neutron-deficient nuclei around $A\approx90$ and near the $N \approx Z$ line exhibits rapid changes in nuclear structure, including shape coexistence and strong proton-neutron correlations. These nuclei provide key insights into shell evolution, deformation effects, and the underlying nuclear interactions, and serve as important benchmarks for theoretical models.

In this work, we present recent mass measurements of neutron-deficient Ru and Pd isotopes performed at the FRS Ion Catcher (FRS-IC) at GSI. The experiments combine in-flight separation of projectile fragments with stopping in a cryogenic stopping cell (CSC) and high-resolution measurements using a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS), allowing access to nuclei with low yields and short half-lives.

Recent measurements include a direct mass measurement of $^{89}\mathrm{Ru}$, showing that the measured value deviates by more than 10 standard deviations (361(35) keV) from the previous result, while misidentification has been excluded using advanced identification techniques. This provides a reliable basis for extracting one-proton separation energies and reveals structural effects consistent with a deformed subshell gap near $Z = 38$.

Furthermore, the mass of $^{93}\mathrm{Pd}$ was measured directly for the first time, reducing the uncertainty by an order of magnitude. In combination with available spectroscopic information and decay data, these results indicate that the excitation energy of the parent state associated with the one-proton (1p) and two-proton (2p) decay branches in $^{94}\mathrm{Ag}$ differ by about 10 standard deviations, indicating that these decay modes do not originate from the same nuclear state. This finding calls into question the proposed decay scheme of two-proton decay and suggests the presence of multiple structurally distinct high-spin configurations, challenging previous interpretations of decay mechanisms in this region.

The neutron-rich rare-earth nuclei form a pronounced region of the nuclear chart associated with prolate deformation. The shape evolution of these open-shell nuclei are intrinsically dependent on the neutron/proton number and consequently the underlying single-particle structure [1], and its interplay with collective phenomena such as deformation. K-isomerism, in combination with $\gamma$ ray spectroscopy, serves as a powerful tool to probe the nature of single-particle structures and the low-lying excitation energy spectrum below the isomer. An experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung GmbH in Darmstadt, Germany, at the final focal plane of the GSI FRagment Separator, with the Decay Spectroscopy setup [2]. A primary beam of $^{170}$Er was fragmented to produce nuclei in the ranges $62 \leq Z \leq 67$ and $94 \leq N \leq 102$. Our recent spectroscopic results are the identification of a new isomeric state of $^{157}$Sm and $^{164}$Tb. The measured observables provide insight into the developing single-particle structures and shedding new light on the evolution of deformation in this mass region.

[1] Yusuke Tsunoda, Takaharu Otsuka, Noritaka Shimizu, Michio Honma, and Yutaka Utsuno. Physical Review C, 89(3):031301, 2014.
[2] A. K. Mistry et al. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1033:166662, 2022.

Research on the nuclear structure near the doubly magic isotope $^{132}$Sn continues to engage significant experimental and theoretical efforts. Investigating nuclear interactions in the vicinity of the proton ($Z=50$) and neutron ($N=82$) shell closures presents a unique opportunity to enhance our understanding of nuclear structure properties within this exotic region of the nuclear chart. However, experimental data in this area, particularly concerning the half-lives of low-lying excited states, remains limited. Most available spectroscopic data are derived from studies of nuclear states populated through $\beta$-decay of a parent nucleus or $\gamma$-ray spectroscopy following the decay of a long-lived isomeric state. This abstract discusses the in-beam $\gamma$-ray spectroscopy method, which utilizes nucleon knock-out reactions that can populate previously unobserved states. Additionally, this method focuses on prompt $\gamma$-rays emitted after the knock-out reaction, making it an ideal tool for investigating the half-lives ($T_{1/2}$) of low-lying excited states down to a few picoseconds, which often elude fast timing techniques.

Nuclei of interest were produced in the Radioactive Isotope Beam Factory at RIKEN during the HiCARI campaign [1]. Excited states were populated in the $^{9}Be(^{130}In,^{129}In)$, $^{9}Be(^{130}In,^{128}Cd)$, $^{9}Be(^{131}In,^{128}Cd)$, $^{9}Be(^{129}Cd,^{128}Cd)$ nucleon knock-out reactions following in-flight fission of a $^{238}U$ primary beam. In close geometry relative to the $^{9}Be$ target, an array of segmented HPGe detectors [1] was installed for $\gamma$-ray detection. Based on the reconstructed velocity of the ions and position of $\gamma$-ray emission during their de-excitation event-by-event, $\gamma$-ray spectra were obtained for each reaction channel. The line shape of identified transitions carries information regarding their energy ($E$) and $T_{1/2}$. Taking into account precisely measured HiCARI geometry, the response function of every HPGe crystal to the $\gamma$-ray of given $E$ and $T_{1/2}$ was simulated using the Geant4 package [2]. Finally, $E$ and $T_{1/2}$ were extracted by minimizing the $\chi^{2}$ of response functions fitted to the experimental data. To validate more complex reaction channels, a relatively simple case, $^{9}Be(^{132}Sn,^{131}In)$, was used as a benchmark to develop advanced analysis procedures. Further details on $T_{1/2}$ extraction are available in [3].

Taking advantage of multiple reaction channels, the most important scientific output of this analysis is $T_{1/2}$ of 4$^{+}$ and 2$^{+}$ states in $^{128}$Cd, along with observation of two new states and their tentative incorporation into the up-to-date known level scheme. Regarding the case of excited states in $^{129}$In due to a conservative approach to experimental uncertainties, various upper limitations on $T_{1/2}$ of known excited states were extracted, and one previously unobserved transition was tentatively assigned. Results will be interpreted using state-of-the-art shell-model calculations.

[1] K. Wimmer {\it et al.}, RIKEN Accelerator Progress Report 54 (2020) S27.

[2] L. A. Riley{\it et al.}, NIM A 1003, 165305 (2021).

[3] J. Acosta, A. Jungclaus{\it et al.}, Phys. Rev. C 111, 064316 (2025)

The sudden onset of deformation in $A\approx100$ nuclei at $N=60$ has been described as a ground-state shape transition that has raised a lot of interest over the years from an experimental and theoretical point of view [1]. This transition is most pronounced in the Zr and Sr isotopic chains where the low-energy excited-state structure shows significant signs of deformation developing at $N=60$, as opposed to the spherical-like structure observed at $N\leq58$.

At present, the two most promising theoretical interpretations of this phenomenon are given by the Monte Carlo Shell Model (MCSM) [2] and the Interacting Boson Model with Configuration Mixing (IBM-CM) [3]. The MCSM calculations interpret the structure of $^{100}$Zr within a multiple-shape-coexistence scenario with several distinct deformed shapes predicted for the lowest $0^+$ states, with rotational bands built on top of them. In contrast, the IBM-CM calculations predict a weakly-deformed "intruder" ground-state configuration in $^{100}$Zr, with corresponding $\beta$ and $\gamma$ bands, and a low-lying spherical "normal" configuration.

In order to test these theoretical models an experiment was performed at the TRIUMF-ISAC facility to investigate the structure of $^{100}$Zr following the $\beta$ decay of $^{100}$Y by utilizing the GRIFFIN $\gamma$-ray spectrometer [4]. The 15 HPGe clover detectors of GRIFFIN were coupled with seven LaBr$_3$ detectors for fast-timing lifetime measurements using the Generalized Centroid Difference method [5].

Mainly low-spin excited states were populated in the $\beta$ decay of the $1^-$ state in $^{100}$Y. This allowed for the lifetimes of several key non-yrast excited states in $^{100}$Zr, including those of the $2^+_3$, and $0^+_3$ states, to be extracted for the first time in this study. These new results will be presented and compared to the MCSM and IBM-CM theoretical predictions.

[1] P.E. Garrett et al., Prog. Part. Nucl. Phys. 124 (2022) 103931.

[2] T. Togashi et al., Phys. Rev. Lett. 117 (2016) 172502.

[3] N. Gavrielov et al., Phys. Rev. C 99, 064324 (2019).

[4] A.B. Garnsworthy et al., Nucl. Instrum. Methods Phys. Res., Sect. A, 918 (2019).

[5] J.-M. Régis et al., Nucl. Instrum. Methods Phys. Res., Sect. A, 726 (2013).

The neutron-deficient nuclei in the vicinity of the Z = 82 shell closure represent one of the most intriguing areas of nuclear chart, where the interplay between single particle and collective degrees of freedom exhibit various nuclear-structure phenomena such as shape coexistence [1], presence of magnetic rotation (MR) bands [2] and isomers [3]. In this region, nuclear shapes gradually evolve from spherical near the neutron shell closure to more deformed configurations near the neutron mid-shell [4]. The studies of odd-mass At (Z = 85) and Bi (Z = 83) isotopes have reported this shape transition with the decreasing neutron numbers [5-7]. Investigations of odd-odd Bi and At isotopes are therefore important to understand the effect of neutron coupling and the effective proton-neutron interaction at the mid-shell. However, exploring the structures of odd-odd neutron-deficient At nuclei remains challenging due to the difficulties in the population and several possible configurations arising from the multiparticle - multihole couplings.

The ground states of odd-odd Bi and At have a spin-parity of 3$ ^+ $, originating from the coupling of proton h$ _{9/2} $ and neutron p$ _{3/2} $ orbitals. In addition, 7$ ^{+} $ and 10 $ ^{-} $ $ \alpha $-decaying isomeric states have also been observed in several odd-odd Bi and At isotopes. The high-spin spectroscopic studies around A $ \approx $ 190-200 have revealed non-collective states, strongly coupled rotational bands and MR band built on either 7$ ^{+} $ or 10 $ ^{-} $ states [8,9]. In contrast, for $ ^{196} $At (N = 111), only one isomeric state (5$ ^{+} $) has been reported above the 3$ ^{+} $ ground state so far. Nothing is known above that level [10]. Moreover, the $ \alpha $-decay studies of $ ^{200} $Fr indicate the existence of single $ \alpha $-decaying 3$ ^{+} $ ground state for $ ^{196} $At [11]. Therefore, investigations of both the high and low spin structures of $ ^{196} $At will be important to understand the evolution of nuclear structure at the neutron number 111.

An experiment using RITU gas-filled separator was performed in the Accelerator Laboratory of the University of Jyväskylä to populate $ ^{196} $At via the reaction - $ ^{165} $Ho ($ ^{36} $Ar, 5n) $ ^{196} $At at a beam energy of 186 MeV. The aim was to investigate the level structures of $ ^{196} $At above the 3$ ^{+} $ ground state and (5$ ^{+} $) isomer using the JUROGAM 3 array and FPGe (Focal Plane Germanium) detectors. The levels above 5$ ^{+} $ isomer have been identified through prompt and delayed spectroscopy and recoil-decay tagging methods which connect to high spin states.

Additionally, in this experiment, the novel detector SIGMA (Segmented Inverted-coaxial GerMAnium) was installed in place of a Broad Energy Germanium Detector at the focal plane [12]. The detector provides the added capability to detect and track the spatial origin of $ \gamma $-rays, which can be further used to correlate and/or veto events. The results demonstrating the performance of SIGMA as a spectroscopic detector as well as a tracking detector in the focal plane will also be presented.

References:

[1] J. Ojala et. al. In: Commun Phys 5, 213 (2022)

[2] R. M. Clark and A. O. Macchiavelli. In: Ann. Rev. Nucl. Part. Sci. 50.1 (2000), 1–36

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The complex nature of the nucleon-nucleon interaction allows for spherical, oblate and prolate deformations to appear at similar energies within the same nucleus. This phenomenon, known as shape coexistence, is widespread across the nuclear chart and it provides a crucial role in understanding nuclear structure [1].

In our study we complement shell-model calculations [2] with beyond-mean-field Hartree-Fock-Bogoliubov techniques [3] to shed light on the rich coexistence of differently deformed structures. We infer shape coexistence from multiple observables such as: quadrupole moments, $E2$ transitions, collective wavefunctions, and shape invariants. The combination of all these hints allows us to understand the complexities of shape coexistence and the notion of nuclear shape itself.

Particularly, the shape invariants provide a model-independent framework to quantify the deformation parameters and their fluctuations [4], which are significant in most nuclei. We analyze how nuclear shapes evolve across the band using an extended sum-rule method to compute the shape invariants for $J\neq0$ states, both for even and odd mass nuclei. This method sheds light on long-standing questions, such as whether doubly-magic nuclei are truly spherical, whether truly rigid triaxial nuclei exist, and how axially symmetric prolate and oblate nuclei really are.

For instance, the doubly-magic nucleus $^{40}$Ca presents shape coexistence between the spherical ground state, the normal deformed rotational band ($3.4$ MeV) and the superdeformed rotational band ($5.2$ MeV) [5]. We analyze the fluctuations of the deformation parameters associated to these states, showing the complexities of the ground state and checking the validity of the perfect rotor approximation for rotational bands.

$^{28}$Si presents a competition between the oblate ground state and the excited prolate rotational band ($6.5$ MeV), with a possible superdeformed structure at higher energies ($\sim10$-$20$ MeV). We find that $sdpf$ excitations are needed to correctly describe $^{28}$Si and that superdeformed shapes appear at 18-20 MeV [6].

[1] P. E. Garrett, M. Zielińska, and E. Clément, Prog. Part. Nucl. Phys. 124, 103931 (2022).

[2] E. Caurier and F. Nowacki, Acta Phys. Pol. B 30, 705 (1999).

[3] B. Bally, A. Sánchez-Fernández, and T. R. Rodríguez, Eur. Phys. J. A 57, 69 (2021).

[4] A. Poves, F. Nowacki, Y. Alhassid, Phys. Rev. C 101, 054307 (2020)

[5] E. Caurier, J. Menéndez, F. Nowacki, and A. Poves, Phys. Rev. C 75, 054317 (2007).

[6] D. Frycz, J. Menéndez, A. Rios, B. Bally, T. R. Rodríguez, and A. M. Romero, Phys. Rev. C 110, 054326 (2024).

Time-dependent density functional theory (TDDFT) provides a fundamental framework for describing nuclear collective time-dependent processes, ranging from small-amplitude collective oscillations to large-amplitude phenomena such as fission and heavy-ion reactions. However, due to its mean-field nature, TDDFT accounts only for one-body dissipation effects and fails to describe the spreading widths of one-body observables.

To address this limitation, we develop the configuration-interaction time-dependent density functional theory (CI-TDDFT). This method expands the nuclear wave function in terms of a set of correlated time-dependent Slater determinants and rigorously follows the Dirac–Frenkel time-dependent variational principle. As a first application, we present an illustrative study of the excitation energies and widths of giant monopole resonances in 58Ni and 60Ni. Compared to TDDFT, CI-TDDFT provides a more accurate description of the widths of giant monopole resonances.

The isomeric cross-section ratio R = σm/σg for the ¹⁹⁷Au(p,n)¹⁹⁷m,gHg reaction is analyzed over the proton energy range 6.5–32.0 MeV using selected published experimental datasets retrieved from the EXFOR nuclear reaction database and primary publications. Cross-sections calculated with the TALYS-1.9 nuclear reaction code, taken from the TENDL-2019 evaluated nuclear data library (Plompen et al., 2020), are compared with the experimental data. The analysis reveals that TENDL-2019 systematically underestimates the isomeric ratio above 14 MeV by 15–25%, motivating a detailed examination of the angular momentum and spin-cutoff parameter physics that govern isomeric state population. The large spin asymmetry between the isomeric state (¹⁹⁷mHg, Jπ = 13/2+, T½ = 23.8 h) and the ground state (¹⁹⁷gHg, Jπ = 1/2⁻, T½ = 64.14 h) makes this reaction an extreme example of spin-dependent level density sensitivity, directly connecting to the conference theme of nuclear extremes. The spin-cutoff parameter σ² is evaluated analytically using three published level density parameterizations, namely, Gilbert–Cameron, back-shifted Fermi gas, and microscopic HF-BCS—and its role in controlling the energy dependence of R is discussed in the context of the TENDL-2019 discrepancy.

Coulomb-excitation measurements provide a direct and model-independent probe of electromagnetic matrix elements, which are essential for understanding collective motion, shape coexistence, and configuration mixing in atomic nuclei [1]. The extraction of these quantities relies on a global least-squares analysis of experimental γ-ray yields against calculated excitation probabilities, where the absolute normalization plays a critical role in determining the final matrix elements and their uncertainties. Consequently, a statistical estimation of the uncertainties in the multidimensional χ2 minimization is crucial for ensuring the reliability of nuclear-structure information obtained from such analysis.
In this context, the semiclassical coupled-channels code GOSIA is widely used for Coulomb-excitation analysis, performing a simultaneous fit of electromagnetic matrix elements and normalization parameters through minimization of a global χ2 function [2]. The normalization coefficients, which connect calculated yields to measured intensities, are strongly correlated with the fitted matrix elements. As a result, their uncertainties propagate non-trivially into the extracted physical observables. In the typical GOSIA approach, parameter uncertainties are obtained from the linearization of the χ2 surface around its minimum using the Δχ2 criterion. However, this procedure relies on several internal approximations in the treatment of normalization, which may influence the estimated uncertainties and parameter correlations. Additionally more and more often in the analysis of Coulomb excitation of exotic nuclei with a modified version of the code GOSIA2, a manual two-dimensional error estimation is performed as it was described by Zielińska et al. [3].
In this work, we present a Monte Carlo (MC) based study of the χ2 normalization error estimation in GOSIA. Starting from a set of a priori electromagnetic matrix elements, ensembles of synthetic experimental yields are generated using MC method by incorporating realistic statistical fluctuations [4]. These pseudo-data sets are then analyzed using the standard GOSIA framework, allowing the propagation of statistical uncertainties through the full fitting procedure to be examined. By comparing the distribution of fitted parameters with the nominal Δχ2-based uncertainties, we assess the impact of approximations in the normalization treatment and quantify their effect on extracted matrix elements.
The present study provides insight into the robustness of the current error-estimation methodology and highlights potential limitations in the treatment of normalization within GOSIA. In particular, the MC approach offers a systematic framework for benchmarking the statistical reliability of Coulomb-excitation analysis and for investigating possible improvements to the normalization procedure and uncertainty evaluation. The results of this study will be presented and discussed in the context of their impact on the extraction of electromagnetic matrix elements.

References:
[1] K. Alder, A. Bohr, T. Huus, B. Mottelson, and A. Winther, Rev. Mod. Phys. 28, 432 (1956).
[2] T. Czosnyka, D. Cline, and C. Wu, Bull. Am. Phys. Soc. 28, 745 (1982).
[3] M. Zielińska et al., Eur. Phys. J. A 52, 99 (2016).
[4] Siegmund Brandt, Data Analysis - Statistical and Computational Methods for Scientists and Engineers, 4th ed., Springer (2014).

Accurate neutron-capture and photodisintegration reaction rates obtained within the Hauser-Feshbach statistical framework depend critically on the nuclear $\gamma$-ray strength function and nuclear level density. Uncertainties in these quantities propagate directly into Maxwellian-averaged cross sections and remain a major source of uncertainty in modeling $r$-process nucleosynthesis. In this work, we investigate the impact of low-lying pygmy dipole strength on electric dipole transitions and its consequences for $(n,\gamma)$ and $(\gamma,n)$ reaction rates in neutron-rich nuclei. The $\gamma$-ray strength functions are calculated using a fully self-consistent relativistic quasiparticle random-phase approximation based on the DD-PCX energy density functional and are subsequently employed in Hauser-Feshbach calculations of astrophysical reaction rates. We demonstrate that reaction-rate enhancements are governed greatly by the energetic alignment of the pygmy dipole strength with the neutron separation threshold, rather than only by the total amount of low-energy dipole strength. When the pygmy mode lies close to the neutron threshold, neutron capture and photodisintegration reactions are significantly affected. We find pronounced rate enhancements in nuclei such as $^{68}$Ni and $^{132}$Sn, where this alignment occurs, while thermal averaging reduces large local cross-section enhancements to more moderate but still astrophysically relevant rate increases. For photodisintegration reactions, pygmy dipole effects become important in very neutron-rich nuclei with low neutron separation energies, again leading to the notable modifications when dipole strength and threshold energies coincide. These results underline the crucial role of a realistic microscopic description of low-energy dipole strength near the neutron threshold for predictive $r$-process modeling and emphasize the need for close synergy between theory and experiments probing dipole response in neutron-rich nuclei.

Decoherence leads to the loss of quantum correlations in entangled systems due to interactions with surrounding matter. While entanglement and its decoherence is well established in the optical photonic regime, its behaviour at the MeV energy scale, such as $\gamma$-ray pairs produced in positron annihilation, is far less well established and with only limited experimental evidence to date.
This question of the fundamental nature of entanglement and decoherence is also foundational for developing the next generation of Positron Emission Tomography (PET), where annihilation photons are used for image reconstruction. Image quality is degraded by scattering and random coincidences, reducing spatial resolution and accuracy [1].

Evidence that entanglement of annihilation gamma is robust, at least for single Compton scattering processes [2], challenges the previous expectation of rapid decoherence.
This motivates the use of Compton polarimetry to access polarisation dependent scattering correlations. Advances in highly segmented $\gamma$-ray detector systems [3, 4] have demonstrated sensitivity to photon polarisation via azimuthal scattering distributions, opening a path for potential applications in PET imaging.

The current study aims to investigate the evolution of entanglement in MeV-scale $\gamma$-ray pairs, focusing on double and triple Compton scattering of annihilation photons with potential to progress to higher order scattering. The data were collected using the GRIFFIN spectrometer at TRIUMF-ISAC [5], combined with an array of Double-sided Silicon Strip Detectors (DSSD) for coincidence measurements. Compton polarimetry is used to probe the effects of entanglement on polarisation dependent correlations following prior sequential scattering events. Preliminary results will be presented and the prospects for the project to better constrain the nature of decoherence over a broad kinematic range will be outlined.

References:

[1] D.P. Watts, J. Bordes, J.R. Brown, A. Cherlin, R. Newton, J. Allison, M. Bashkanov, N. Efthimiou and N. A. Zachariou, Photon quantum entanglement in the MeV regime and its application in PET imaging, Nat. Commun., 12, 2646 (2021)

[2] J. Bordes et al, First Detailed Study of the Quantum Decoherence of Entangled Gamma Photons, Phys. Rev. Lett. 133, 132502 (2024)

[3] B. Alikhani, A. Givechev, A. Heinz, P.R. John, J. Leske, M. Lettmann, O.Möller, N. Pietralla, C. Röder, Compton polarimetry with a 36-fold segmented HPGe-detector of the AGATA-type,
Nucl. Instrum. Methods Phys. Res. A, 675 (2012)

[4] C. Morse, H.L. Crawford, A.O. Macchiavelli, A. Wiens et al., The polarization sensitivity of GRETINA, Nucl. Instrum. Methods Phys. Res. A, 1025, 166155 (2022)

[5] A.B. Garnsworthy, C.E. Svensson, M. Bowry, R. Dunlop, A.D. MacLean, B. Olaizola, J.K. Smith et al., The GRIFFIN facility for Decay-Spectroscopy studies at TRIUMF-ISAC, Nucl. Instrum. Methods Phys. Res. A, 918 (2019)

Deuteron–deuteron fusion at very low energies is relevant both for nuclear astrophysics and for prospective fusion-energy applications [1]. The reaction cross section decreases sharply with decreasing projectile energy due to the Coulomb barrier; however, in metallic targets, electron screening significantly enhances the barrier penetration probability [2]. Recent studies have suggested that the cross section of the low-energy DD reaction can also be influenced by a narrow threshold resonance in 4He [3,4]. This single-particle-like resonance is expected to decay predominantly through internal pair creation (IPC), producing electron–positron pairs with a total energy of approximately 23 MeV. Earlier experimental studies employed thin single-silicon detectors to identify
the signature of this IPC by the analysis of the partial absorption peak [5,6,7]. However, extending the branching-ratio measurement for deuteron energies below 10 keV remains a challenge due to the rapidly decreasing reaction cross section and contributions from different background components in the relevant detector-response region.

In the present work, a silicon detector telescope operated at the ultra-high-vacuum accelerator facility of the University of Szczecin is employed to reduce background and study the IPC channel. The background response of the detector was characterized using dedicated measurements and Monte-Carlo simulations. The dependence of the background-response function and its time-dependent fluctuations on detector orientation and shielding were investigated. The cosmic-ray component was modelled using the CRY generator coupled to Geant4 simulations [8]. The terrestrial gamma component was mapped independently with a large-volume NaI(Tl) detector and used to model the response function in the Si detectors. In addition, the neutron-induced beam background was evaluated and incorporated into the final analysis. The use of the ΔE–E telescope provided further background suppression and improved the reliability of the IPC signal extraction.

Based on this combined analysis, the electron–proton branching ratio was determined down to Elab =3.5 keV, and its energy dependence was extracted over the measured range. The obtained values support the predicted enhancement of the IPC channel toward very low energies, approaching an electron–proton branching ratio of the order of 10. The IPC channel was also studied in Zr and Pd metallic targets, establishing the material dependence of the electron–proton branching ratio. These results extend the available experimental information on the low-energy DD reaction and provide new constraints on the interpretation of the IPC channel in terms of threshold-resonance excitation. The present work also establishes an experimental and analysis procedure for future measurements at still lower energies, where the branching ratio is expected to increase further.
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In recent years, shape coexistence in atomic nuclei has been recognized as ubiquitous across the nuclear chart [1]. The structure of nuclei exhibiting shape coexistence reflects an intriguing interplay between microscopic and macroscopic nuclear effects, the understanding of which is one of the greatest challenges of modern nuclear theory. This interplay manifests in the $A\approx100$ region with neutron number N=60, with the Sr and Zr isotopes exhibiting the most rapid onset of ground-state deformation observed across the nuclear landscape. In this context, $^{96}Sr$ represents a transitional nucleus located at the precipice of the region of deformed ground-state shapes. From a structural point of view, the observed sudden onset of deformation can be explained by an inversion of coexisting regular and “intruder” configurations (multiparticle-multihole excitations) where the former possesses a spherical shape, and the latter is deformed. This interpretation is supported both by theoretical calculations [2,3,4] and experimental data for Sr [5,6]. Notably, the $\gamma$-ray decay transition probabilities of the $2^+_1$ state in $^{96}Sr$ and the $2^+_2$ state in $^{98}Sr$, and the spectroscopic quadrupole moments of these states measured in a Coulomb-excitation study [5,6], were found to be consistent with the $0^+_1(^{96}Sr)\leftrightarrow 0^+_2(^{98}Sr)$ inversion scenario. On the contrary, there is still lack of experimental evidence for the correspondence of the low-lying $0^{+}$ states in $^{96}Sr$ to the ground-state configuration $0^+_1$ of $^{98}Sr$. A neutron-transfer reaction was performed at TRIUMF [7] and spectroscopic factors were measured for the excited $0^{+}$ states. Combining these results with the extremely large $\rho^2(E0;0^+_3\rightarrow 0^+_2)$ value of 160(40) [8] led to a suggestion of triple shape coexistence occurring in $^{96}Sr$, with a weakly deformed ground state and two excited $0^{+}$configurations: a deformed and a spherical one, which undergo strong mixing.
Our new experimental study of $^{96}Sr$ aims to shed light on the inversion scenario via the measurement of transition probabilities in a Coulomb excitation experiment performed at TRIUMF. The $^{96}Sr$ radioactive ion beam was produced and delivered by the ISAC-II facility. The $\gamma$ rays from Coulomb-excited states in $^{96}Sr$ were detected by the TIGRESS spectrometer [9], while the scattered beam ions were detected by the S3 detector of the BAMBINO array [10]. An increase of two orders of magnitude in the statistics of the $2_{1}^{+}\rightarrow0^{+}_{1}$ transition was achieved compared to the previous Coulomb-excitation experiment performed at ISOLDE [5,6]. The population of several states in $^{96}Sr$ was observed, including the $4_{1}^{+}$, $0_{2}^{+}$ and $3_{1}^{-}$ ones. Finally, our Coulomb-excitation experiment provided as well high-quality data on $^{96}Y$, allowing a distinction to be made between single-particle and core-coupled states.
Preliminary results of the ongoing data analysis will be presented.

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[8] T. Kibédi et al., Prog. Part. and Nucl. Phys. 123, 103930 (2022).
[9] G. Hackman and C. E. Svensson, Hyperfine Int. 225 241 (2014).
[10] C. Y. Wu et al., Technical report LNLL/Rochester 2007 TRIUMF activity (2007).

The region around N≈60 with Z≤40 has generated considerable interest as it features the most abrupt shape transition known to date in the nuclear chart, when crossing from N=58 to N=60 [1]. This transition is closely linked to shape coexistence [2], a phenomenon where two or more states with different intrinsic shapes coexist within the same nucleus at low excitation energy and within a narrow energy range. Specifically, the sharp change arises from the inversion of two distinct quantum nuclear configurations, each corresponding to different nuclear shapes. These shifts are interpreted as quantum phase transitions [3], indicating a fundamental transformation in nuclear properties. This phase transition emphasises the importance of nuclear deformations and the variety of shapes present in neutron-rich nuclei such as strontium.
The IS709 experiment at the ISOLDE Decay Station (IDS) [4] aims to investigate the phenomenon of shape coexistence across the N=60 region in $^{96–102}$Sr isotopes, with particular emphasis on $^{100}$Sr. Excited nuclear states were populated via β and β–n decay of Rb beams and studied with 13 Clover HPGe detectors optimised for γ–γ angular correlation measurements [5], allowing a precise determination of transition multipolarities and spin assignments. In parallel, the SPectrometer for Electron DEtection (SPEDE) [6] was employed to measure internal conversion electrons, providing direct access to E0 transition strengths, which jointly enable the identification of excited 0$^{+}$ states.
In this contribution, results from the IS709 experiment are presented which, combined with complementary fast-timing lifetime measurements [7] from the IS622 experiment, integrate high-precision γ–γ angular correlations, internal conversion electron spectroscopy, and lifetime measurements. This combined approach provides the key experimental observables required to determine spins and parities, transition multipolarities, and electromagnetic transition rates, enabling the extraction of nuclear deformation parameters. Together, these measurements offer new insight into shape deformation and shape coexistence in neutron-rich strontium isotopes around N≈60 and demonstrate the broad capabilities and versatility of the IDS setup.

[1] R. Rodriguez-Guzman, P. Sarriguren, and L. M. Robledo. Shape evolution in yttrium and niobium neutron-rich isotopes. Phys. Rev. C, 83, 044307 (2011).
[2] A. Poves. Shape coexistence in nuclei. J. Phys. G: Nucl. Part. Phys. 43, 020401 (2016).
[3] Tomoaki Togashi, Yusuke Tsunoda, Takaharu Otsuka, and Noritak Shimizu. Quantum Phase Transition in the Shape of Zr isotopes. Phys. Rev. Lett. 117, 172502 (2016).
[4] ISOLDE Decay Station, CERN. Available online: https://isolde-ids.web.cern.ch/. Accessed on March 17, 2026.
[5] J.K. Smith et al. Gamma-gamma angular correlation analysis techniques with the GRIFFIN spectrometer. Nuc. Inst. and Methods in Physics Research, A 922 47-63 (2019).
[6] P. Papadakis et al. The SPEDE spectrometer. Eur. Phys. J. A 54, 42 (2018).
[7] J.-M. Régis, G. Pascovici, J. Jolie, M. Rudigier. The mirror symmetric centroid difference method for picosecond lifetime measurements via γ-γ coincidences using very fast LaBr$_{3}$(Ce). Nucl. Instrum. Methods Phys. Res. A 622, 83-92 (2010).

Until recently, many deformed nuclei have been considered to have excitations described by the collective model of Bohr and Mottelson [1]. However, the interpretation that some states have a collective vibrational character has been challenged to the point that it is necessary to ask whether or not two-phonon excitations exist among the low-energy states of atomic nuclei. In particular, experimental evidence for the characteristic Kπ = 0+, 4+ two-γ-phonon doublet
remains limited.

In the rare-earth region, a Kπ = 2+ band-head state is commonly observed and can be identified as the single-phonon γ excitation; however, only a small number of candidates for two-phonon γ-vibrational states have been identified [2–6]. This scarcity, together with the increasing prominence of alternative interpretations for low-lying Kπ = 0+ states such as shape coexistence [7] and rotations around a triaxial ground state [8], motivates a re-evaluation of proposed two-phonon assignments and the applicability of the vibrational model in deformed nuclei.

Dysprosium-162 (Z = 66) is one such nucleus, in which states at 1535 keV and 2181 keV have been interpreted as members of a split Kπ = 4+ two-phonon γ-vibration configuration [2, 9, 10]. Coulomb excitation provides a sensitive probe of these structures, selectively populating states via electromagnetic interactions and enabling the extraction of transition strengths. In this work, results from Coulomb-excitation of 162Dy using an 16O beam at the Heavy Ion Accelerator Facility (HIAF) at the Australian National University are presented [11, 12]. This study forms part of a broader experimental program aimed at probing 162Dy with higher-Z beams to enable multi-step Coulomb excitation
and direct population of states of interest.

In parallel, the development of a new particle-detector array for the CAESAR system at HIAF is underway. This upgrade is designed to improve particle identification and angular coverage, thereby enhancing the capabilities for future Coulomb-excitation measurements at ANU, with initial experiments planned for later this year.

References
[1] A. N. Bohr and B. R. Mottelson. “Collective and individual-particle aspects of nuclear structure”. Mat -fys Medd 27.16 (1953), pp. 1–174.
[2] A. Aprahamian, S. R. Lesher, et al. “Lifetime measurements in 162Dy”. Physical Review C 95.2 (2017), p. 024329.1
[3] F. Corminboeuf, J. Jolie, et al. “Kπ double-gamma vibration in 164Dy”. Physical Review C 56.3 (1997), R1201–R1205.
[4] C. Fahlander, A. Axelsson, et al. “Two-phonon γ-vibrational states in 166Er”. Physics Letters B 388.3 (1996),pp. 475–480.
[5] P. E. Garrett, M. Kadi, et al. “Kπ = 0+ and 4+ Two-Phonon γ-Vibrational States in 166Er”. Physical Review Letters 78.24 (1997), pp. 4545–4548.
[6] T. Härtlein, M. Heinebrodt, et al. “Collective excitations built on the 2+ γ state in 168Er”. The European Physical Journal A - Hadrons and Nuclei 2.3 (1998), pp. 253–261.
[7] K. Heyde and J. Wood. “Shape coexistence in atomic nuclei”. Reviews of Modern Physics 83.4 (2011), pp. 1467–1521.
[8] T. Otsuka, Y. Tsunoda, et al. Prevailing Triaxial Shapes in Heavy Nuclei Driven by Nuclear Tensor Force. 2023.
[9] C. Fahlander. “Double-Phonon γ-Vibration of Deformed Nuclei”. In: The Nucleus: New Physics for the New Millennium. Ed. by F. D. Smit, R. Lindsay, et al. Boston, MA: Springer US, 1999, pp. 185–189.
[10] C. Y. Wu, D. Cline, et al. “Electromagnetic properties of the rotationally aligned band in 162Dy”. Physical Review C 64.6 (2001), p. 064317.
[11] Tom Perissinotto. “Investigating Two-phonon gamma-vibrational States in 162Dy”. Undergraduate Honours thesis. Australian National University, 2024.
[12] Yet to be published.

Shape coexistence -- the concept for which an atomic nucleus may manifest different shapes depending on its excitation energy -- and shape evolution along isotopic chains are widespread phenomena throughout the nuclear chart, but we are still far from their comprehensive knowledge. In this context, the study of electric monopole (E0) transitions, connected to changes in the radial distribution of the charges in a nucleus, is fundamental.

Experimental evidence suggests that Sr and Zr isotopes around N=60 are ideal to study the properties related to the shape of atomic nuclei. For this reason, a dedicated beta-decay experiment was performed at the TRIUMF laboratories in Vancouver, Canada. A radioactive ion beam consisting mainly of 96Rb and 96Sr was produced and implanted at the center of GRIFFIN, a 4pi array of Compton-suppressed HPGe detectors equipped with a suite of ancillary detectors. Following the beta decay of the parent nuclei, the excited states of 96Zr and 96Sr were populated and studied.

In this contribution, the first results of the analysis concerning the low-energy states of 96Sr and 96Zr is presented, with a focus on their relevance in the shape coexistence framework.

The Cr isotopes with N≥28 are a good testing ground for rapid shape evolution from a spherical to a well deformed region close to N=40 [1]. Among the Cr isotopic chain, the $^{56}$Cr (N=32) shows a very particular interest. Shell-model calculations, using various interactions and/or effective charges, are able to reproduce well the trend of the energy of the 2$^{+}_1$ state along the Cr isotopic chain but fail to reproduce the staggering of the B(E2:2$^+_1$ →0$^+_1$) values with a minimum at $^{56}$Cr (N=32) [1]. Beyond mean-field calculations using Gogny interaction reproduce the experimental zigzag behaviour in the Ti isotopes without any need to invoke effective charges but again this is not the case for the Cr isotopes [2]. Calculations performed with the AMD+HFB framework [3] aiming to investigate the triaxial deformation of the states and shape coexistence in this region reproduce the ‘staggering’ of B(E2) values at N=32 but the theoretical values of B(E2) remain much higher than the experimental values [4].
To get an insight into the structure $^{56}$Cr, shape coexistence and triaxial deformation were studied in a recent experiment via lifetime measurements of the 0$_2^+$ and 2$_2^+$ states. The states of interest were populated using a two-neutron transfer reaction: $^{54}$Cr($^{18}$O,$^{16}$O)$^{56}$Cr. Gamma rays were measured using the state of the art of gamma-ray spectroscopy, the AGATA array [5], coupled with the SPIDER silicon detector [6] to reach the needed channel selectivity. Experimental results will be discussed and compared to theoretical calculations.

[1] M. Seidlitz et al., Phys. Rev C 84, 034318 (2011).
[2] T.R. Rodriguez and J. Luis Edigo, PRL 99, 062501 (2007).
[3] Y. Kanada-En’yo et al., C.R. Physique 4 (2003) 497-520
[4] M. Kimura, Presentation at TNP meeting.
[5] J. J. Valiente Dobón et al., Nuc. Instr. and Meth. A 1049 (2023) 168040
[6] M. Rocchini et al., Nucl. Instr. and Meth. A 971 (2020) 164030

The emergence of collectivity can be explored by studying nuclei that differ from closed-shell configurations by a few particles or holes, involving both protons and neutrons. In this context, the regions around the doubly magic nuclei ²⁰⁸Pb and ¹³²Sn provide ideal testing grounds for such investigations. This can be achieved by measuring the electric quadrupole moments associated with the first pure E2 excitations, as well as the E2 components of the first mixed M1 + E2 transitions.

In the ²⁰⁸Pb region, for the ²⁰⁹Po (2p–1h), ²¹¹Rn (4p–1h), and ²¹³Ra (6p–1h) isotones, a systematic increase of the E2 transitions strength was found, originating from growing contributions of additional protons along the N=125 chain [1]. Similarly, in the ¹³²Sn region, an increase of collectivity was observed in ¹²⁹Sb for the states of the 2⁺(¹²⁸Sn)⊗πg_7/2 multiplet with respect to the ¹²⁸Sn core [2]. Recently, the lifetime of the analogous 2⁺(¹³⁰Sn)⊗πg_7/2 state in ¹³¹Sb was measured by our collaboration [3]. The deduced probability of the E2 transition showed a value similar to that of the ¹³⁰Sn core, in accordance with the weak-coupling limit, but in contrast with the ¹²⁹Sb results. To shed more light on this behavior, in the present work the electric quadrupole transition probabilities were investigated in the ¹³¹I and ¹³³I isotopes, which contain two additional protons compared with the ¹²⁹Sb and ¹³¹Sb nuclei, respectively.

The ¹³¹I and ¹³³I isotopes were produced during the thermal neutron induced fission of a ²³⁵U target at the Institut Laue-Langevin (ILL). The isotopes of interest were separated from all fission products using the LOHENGRIN spectrometer [4] according to their A/q and E/q mass-to-charge and energy-to-charge ratios. The 11/2⁺ and 5/2⁺ states, which decay via E2 and M1+E2 transitions, respectively, in ^131,133I, were populated via the β-decay of ^131,133Te isotopes. The lifetimes of the 11/2⁺ and 5/2⁺ levels were measured using the fast-timing technique [5] with two HPGe clover detectors and four LaBr₃(Ce) scintillators.

The lifetimes of the low-lying states in the ¹³³I isotope were measured for the first time in the present analysis. The corresponding states in ¹³¹I were remeasured with high precision. For both nuclei, a systematic increase in collectivity beyond the weak-coupling limit was observed. The experimental results will be supported by realistic shell-model calculations, providing deeper insight into the nature of the emergence of collectivity in the vicinity of the doubly magic ¹³²Sn nucleus.

References:

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In this work, the new observation of an isomer in $^{73}$Co is reported. The $T_{1/2}=202(20)\ \mu\textnormal{s}$ isomer at 1178 keV was observed using the FRIB Decay Station initiator (FDSi) at the Facility for Rare Isotope Beams (FRIB). This isomer is driven by a $1/2^-$ deformed 1p-2h proton intruder state, and has analogous configurations in lower-mass Co isotopes. In $^{69}$Co, the deformed isomer is energetically near the spherical g.s. Several state-of-the-art shell-model calculations predict inversion of this isomer with the g.s. in the $N=40-50$ region. The new observation at 1178 keV indicates an increase in the energy away from inversion. Here, complementary calculations are compared with the new observation in mind, exposing challenges in predicting inversion in the $N=40-50$ region. The presented results suggest there is no island of shape inversion from this proton-driven intruder state in the cobalt isotopes approaching $N=50$.

Among challenging problems in physics is the understanding of emergent collective excitation modes in interacting quantum many-body systems in terms of the microscopic degrees of freedom. The study of evolution of properties of nuclei, as function of excitation energy, angular momentum and isospin, open avenues to search for simple patterns to identify and better understand hidden aspects of the nucleus.

Among various phenomenon, nuclei can also vibrate in surprisingly ordered ways. Vibrations that have played a central role in revealing nature’s fundamental laws, can be explored starting from things as simple as a pendulum to more complex gravitational waves. In nuclei phonons represent quantized collective excitations. Multiphoton states occur when two or more phonon are excited. The study of multi-phonon excitations opens a window into the collective dynamics of many-body systems, whether they be atoms in a solid or nucleons in a nucleus. The investigations and the evolution of the structure moving away from stability and the study of difficult to study odd-odd nuclei, where orderly collective motion is usually hidden by chaotic individual particle behaviour, could help to better understand the driving force of valence neutrons and protons and the dynamical behaviour of surface vibrations.

In this talk will discuss the structural evolution of the neutron-rich Nb isotopes as a function of spin and isospin. The neutron-rich Nb isotopes studied here were produced as fission fragments in reactions with a $^{238}$U beam at 6.2 MeV/u on a $^{9}$Be target at GANIL. The spectrometer (VAMOS++) coupled to a γ-ray tracking array AGATA along with the EXOGAM array, were used to identify the excited states of the fission fragments. These measurements were combined with independently obtained high-fold γ-ray coincidence measurements employing a $^{252}$Cf source at Gammasphere array (when at LBL, USA). These powerful complementary techniques allowed the characterization of the Nb isotopic chain all the way till $^{109}$Nb. The present measurements allowed to investigate the evolution of these isotopes very far from the valley of stability and demonstrate the first evidence illustrating the robustness of vibration excitations in the presence of an odd valence proton and neutron including possible coexisting shapes beyond the N=60 transitional region.

Gamma-ray spectroscopy is a powerful tool to measure electromagnetic observables offering a glimpse into the structure of neutron-rich nuclei. The advent of $\gamma$-ray tracking arrays like AGATA has indeed opened new possibilities in this field, in particular when AGATA is coupled to setups providing a high sensitivity for weak reaction channel selection.
Since 2022, the second AGATA physics campaign at LNL is ongoing. The study of neutron-rich nuclei with fusion-fission and multi-nucleon transfer reactions has been one of the main subjects tackled. The AGATA-PRISMA setup measured $\gamma$ rays emitted by the reaction products identified in mass and atomic number in PRISMA on an event-by-event basis.
In the talk, we will present results from several experiments already performed, exploiting fusion-fission reactions with a $^{208}$Pb beam and multi-nucleon transfer reactions with a variety of beams. Neutron-rich nuclei were explored around the N=20-28, N=40, N=50 and N=126 (sub)shell closures, measuring both level energies and lifetimes, helping to understand shell structure evolution in these key regions of the Segrè chart.

The region around the doubly magic nucleus 100Sn provides a unique testing ground for nuclear structure models at the proton drip line and near the (N=Z) line. Recent experiments performed at the Radioactive Isotope Beam Factory (RIBF), Japan, using the DALI2+ gamma-ray spectrometer have enabled new spectroscopic studies in this key region.

In this contribution, I will report on the first in-beam gamma-ray spectroscopy of 100Sn. Excited states were populated via proton-induced neutron-knockout reactions from neutron-deficient 101,102Sn isotopes, providing the first direct information on the excitation spectrum of this doubly magic nucleus. The results offer new insights into the robustness of the (Z=N=50) shell closures and the nature of proton and neutron excitations across the shell gaps.

In addition, recent Coulomb-excitation measurements of 98Pd, 100Cd, and 102Sn along N=52 will be presented. The extracted transition strengths, together with large-scale shell-model calculations, provide stringent constraints on the effective proton and neutron charges in the vicinity of 100Sn. The results indicate enhanced neutron polarization effects and contribute to a consistent description of quadrupole collectivity in this region.

The experimental findings will be discussed in the broader context of shell evolution, effective charges, and the doubly magic character of 100Sn.

The yrast negative-parity states of the T$=1/2$ mirror pairs $^{35}$Cl–$^{35}$Ar and $^{39}$K–$^{39}$Ca display Mirror Energy Differences (MEDs) exceeding 200 keV at high spin ($J$ ≥ 11/2⁻) [1,2]. This is in contrast to the <100 keV deviations characteristic of positive-parity states in this mass region. Existing shell-model decompositions attribute the high-$J$ enhancement to the electromagnetic spin–orbit (EMSO) term, which is single-particle in origin and maximized for the cross-shell $0d_{3/2}\to 0f_{7/2}$ excitation [1,3]. Direct experimental constraints on the single-particle content of the relevant intruder states have remained limited.

Three single-neutron transfer measurements addressing this question will be discussed and reported. Simultaneous $^{34g}$Cl($d$,$p$) and $^{34m}$Cl($d$,$p$) reactions were performed with the HELIOS spectrometer and two different ground-state to isomeric-state beams produced by the ATLAS in-flight facility [4]. The $^{38}$K($d$,$p$)$^{39}$K reaction was also measured with the ISOLDE Solenoid Spectrometer (ISS) located at the HIE-ISOLDE facility at CERN. In both cases, angular distributions were extracted from the proton spectra and analyzed within a DWBA framework, confirming $\ell=3$, $0f_{7/2}$ neutron transfer to the yrast 11/2⁻ and 13/2⁻ states in $^{35}$Cl and $^{39}$K. The aligned 13/2⁻ configuration carries the dominant single-neutron strength in both mirrors. Setting C$^2$S(13/2⁻) = 1, the values for the lower-$J$ negative-parity states ($J$ = 7/2⁻ – 11/2⁻) were found to have C$^2$S $\lesssim 0.2$. Therefore, the extracted spectroscopic factors have a direct correlation with the magnitudes of the experimental MEDs, consistent with the aligned ($0d_{3/2}$)$^2$($0f_{7/2}$)$^1$ neutron configuration and the EMSO term as the structural origin of the large high-$J$ MEDs in the $A=35$ and $A=39$ $T=1/2$ systems.

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The structure of neutron-deficient nuclei in the vicinity of 70Br provides a sensitive testing ground for investigating shape evolution, proton–neutron correlations, and isospin-symmetry breaking through Coulomb energy differences. To address these questions, an experiment was performed at the Heavy Ion Laboratory of the University of Warsaw. Excited states in nuclei around A≈70 were populated in fusion–evaporation reactions induced by an 88 MeV 32S beam on a 40Ca target. The experiment took advantage of the complex detector system, recently upgraded by fully digital data acquisition, comprising: the γ-ray spectrometer EAGLE coupled to the neutron and charged-particle detector arrays: NEDA and DIAMANT.
This contribution presents the current status of the data analysis. The performance of the experimental setup is investigated in terms of its sensitivity to weak gamma transitions emitted by evaporation residues produced in particle evaporation reaction channels. The possibility of expanding the spectroscopic information regarding the studied nuclei is discussed.

Understanding nuclear fragmentation reactions of light nuclei (A < 20) in the 100–800 MeV/u energy range represents a key challenge in applied physics. A detailed knowledge of these processes could provide crucial insights for optimizing treatment planning in Particle Therapy and for assessing radiation exposure risks in long-duration human spaceflight. Despite the relevance, experimental databases are still scarcely populated with the corresponding data, forcing to mostly rely on phenomenological descriptions to model nuclear fragmentation reactions. As a consequence, the Monte Carlo codes employed for radiation risk estimation in both Particle Therapy and space radiation shielding carry substantial uncertainties.
The FOOT (FragmentatiOn Of Target) experiment has been conceived to address this gap by conducting a comprehensive campaign of high-precision nuclear fragmentation cross section measurements. The experiment uses light ion beams — from $^1$H to $^{20}$Ne — at energies spanning 100 to 800 MeV/u directed onto targets whose chemical composition mimics human tissue and spacecraft shielding materials. Designed as a fixed-target experiment, FOOT is capable of detecting, tracking and identifying both the primary beam and the resulting nuclear fragments, while fully reconstructing their kinematic properties. This is achieved through a redundant detection strategy that allows measurements to be performed in both direct and inverse kinematics. The final goal is the measurement of double differential cross sections in kinetic energy and emission angle, with maximum uncertainties of 5% and 10% for projectile and target fragmentation, respectively. To accommodate the variety of ion beam facilities where data will be collected, FOOT comprises two portable, complementary setups: an Emulsion Cloud Chamber with wide angular acceptance, optimized for light fragments (Z ≤ 3), and an electronic detector system with narrower angular acceptance suited to heavier ions (3 ≤ Z ≤ 8), incorporating a magnetic spectrometer, a Time-Of-Flight system and a calorimeter.
The FOOT Collaboration has completed the assembly of both setups and has already performed a set of physics data taking. An extensive commissioning phase was carried out to assess performance at the level of individual detectors and full event reconstruction. Both setups have demonstrated highly encouraging results in fragment tracking and ion charge identification, meeting the design requirements of the experiment. In parallel, detailed studies of systematic uncertainties in the event reconstruction pipeline have been conducted on Monte Carlo simulations, leading to the first experimental measurement of the differential fragmentation cross sections of $^{16}$O on C and C$_2$H$_4$ targets. This contribution presents an overview of the FOOT experiment, covering its scientific program, the current status and its planned future developments.

The study of the density dependence of the nuclear equation of state (EOS) at densities above saturation plays a crucial role in understanding a wide range of physical phenomena, both astrophysical, such as the behaviour of neutron stars, and nuclear, such as the formation of the neutron skin. To this end, in March 2025 the ASY-EOS II experiment was conducted at the GSI laboratory in Germany, aiming to provide new and robust constraints on the symmetry energy term of the EOS. The 197Au+197Au reaction was studied at beam energies of 280, 400, 600, and 1000 AMeV using an experimental setup comprising the CHIMERA, KRAB, TOFD, and NeuLAND detectors. The four double rings of the CHIMERA multidetector, transported from the INFN Laboratori Nazionali del Sud (LNS) to GSI, were used in combination with the KRAB detector for reaction plane reconstruction and event centrality selection.
The TOFD detector consists of two structures, one placed along the beam direction and the other located at about 50° in correspondence with NeuLAND. The first TOFD structure was used for reaction centrality selection, while the second was employed as a veto for charged particles in relation to NeuLAND. The NeuLAND detector, composed by 1300 scintillator bars, enabled an effective separation between protons and other hydrogen isotopes, allowing for an accurate determination of neutron–proton observables, in particular elliptic flows. Particular attention was devoted to the calibration of the TOFD (veto) system and the NeuLAND detectors, as well as to techniques for discriminating between neutrons and charged particles; these will be presented.

The Recoil Filter Detector (RFD)[1] is an ancillary device for gamma-ray spectrometers. It measures the time of flight of evaporation residues in coincidence with gamma-rays, providing a significant improvement of gamma spectra by reducing Doppler broadening and excluding unwanted background.
A new version of RFD is being developed for the EAGLE array at the Heavy Ion Laboratory at the University of Warsaw[2]. The ongoing modifications include a significant upgrade of secondary electron detectors made of fast plastic scintillators and segmented SiPM arrays.
The first results from the detector simulation performed with the Geant4 toolkit were reported in [3]. This presentation will show the latest developments of this simulation, with a focus on the light propagation in the scintillator foil and the SiPM, the response of the detector to various radiations, and comparisons with the prototype. The secondary electron beam acceleration and focusing are also explored and optimized using a simulation of the electrostatic lens with the SIMION[4] software.

References

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[2] M. Matejska-Minda et al., Acta Phys. Polon. Supp. 18, 2 (2025).
[3] C. Hiver et al., Acta Phys. Pol. B Proc. Suppl. 19, 1 (2026).
[4] Adaptas Solutions, Simion, https://simion.com (2020).

Atomic nuclei which exhibit a reflection-asymmetric shape are of considerable interest for the understanding of nuclear structure. These "pear-shaped" nuclei are expected to occur in the regions of the nuclear chart where the octupole degree of freedom is enhanced. Strong octupole correlations manifest when the Fermi surface lies close to single-particle orbitals with quantum numbers $[l,j]$ and $[l-3,j-3]$ giving rise to the octupole magic numbers $N,Z=34,56,88$ and $N=134$. Atomic nuclei in these regions can exhibit enhanced particle-hole interactions from the octupole component of the nucleon-nucleon interaction. The electric-octupole (E3) transition rate provides the most unambiguous signature of octupole collectivity, however such measurements are often extremely challenging as E3 transitions compete very weakly against other allowed transitions.

The region around $Z=56, N=88$ possesses the most complete set of B(E3) values across the nuclear chart with the largest values observed in $^{148,150}$Gd however spectroscopic data for the heavier elements is largely missing. Within the N=82 chain, increasing B(E3) strength is observed with increasing proton number from $^{136}$Xe (Z=54) to $^{146}$Gd (Z=64) however it remains unknown whether this trend continues at $^{148}$Dy (Z=66) and beyond or if octupole strength is reduced so far from the octupole magic number Z=56.

To investigate whether enhanced octupole collectivity is present in dysprosium isotopes and extend or constrain the boundaries of enhanced octupole collectivity, we performed a direct measurement of the B(E3) value in $^{148}$Dy. A $\beta$-decay study of $^{148}$Ho was performed at the TRIUMF facility using the GRIFFIN spectrometer. The mean lifetime of the 3$^-$ state was measured using fast-timing methods with LaBr detectors and the absolute $\gamma$-ray branching ratio of the $3^-\rightarrow0^+$ was obtained enabling a direct measurement of the $B(E3;3_1^-\rightarrow0_1^+)$ value.

The dynamics of the nuclear many-body system emerge from an intricate interplay between single-particle motion of individual nucleons and their correlated, collective behavior. The interplay between the two regimes is especially pronounced in the vicinity of semi-magic nuclei, where the onset of collective behavior occurs. An experimental signal for nuclear collectivity in semi-magic even-even nuclei is a strong electric quadrupole ($E$2) transitions between their low-lying states. The same principle holds true in the neighboring odd-even nuclei even though the $E$2 strength is fragmented over many states. Therefore, one effective approach to identify the onset of collectivity is by studying the odd-even neighbors of semi-magic even-even nuclei. The particle-core coupling model is a good framework for studying this concept [1-5]. This was empirically demonstrated in the studies on $^{113,115}$In (a proton hole in Z=50) where their total electric quadrupole strengths are consistent with those of their $^{114,116}$Sn cores [6,7].
However, recent results on $^{129}$Sb have shown significant enhancement of the quadrupole excitation strength compared to its even-even core neighbour $^{128}$Sn, indicating onset of collectivity [8]. The analogous case of $^{129}$Sb in the vicinity of the double-magic nucleus $^{208}$Pb is $^{205}$Bi. Therefore, we have investigated how the sum rule plays out in $^{205}$Bi. In our study we have determined the lifetimes of four excited states of $^{205}$Bi by means of the Recoil Distance Doppler Shift method. The excited states of the nucleus were populated using an 1$p$-transfer reaction. The lifetimes of the $11/2_1^-$, $7/2_1^-$, $5/2_1^-$, $7/2_2^-$ states were determined to be $\leq$ 9.5 ps, 5.6(11) ps, 10(5) ps, and 4.3(5) ps, respectively. The quadrupole strengths of these states were compared in the framework of the particle-core coupling model with the $0_1^+ \to 2_1^+$ transition strength of $^{204}$Pb indicating low quadrupole collectivity in the structure of these states. On the other hand, the shell model calculations failed to reproduce both the ordering of the states and the newly measured transition strengths between them. More surprisingly the same shell model calculations accurately reproduce the excitation energies and level ordering of the low-lying states in $^{207}$Bi. To address the question whether the shell model can consistently describe both the energies and the transition strengths of the low-lying states of $^{207}$Bi, we measured their lifetimes. The results from this experiment compared with the shell-model calculations will be presented and discussed as well.

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The WISArD experiment is a high precision measurement of nuclear beta decay observables to test the existence of Physics Beyond the Standard Model in the weak sector. The angular correlation parameter $a_{\beta\nu}$ and the Fierz interference term $b$ in particular, are very sensitive probes to the existence of exotic scalar or tensor currents, which are not included in the standard V-A theory of the weak interaction. The goal of the WISArD experiment is to measure these parameters in the decay of 32Ar at the challenging level of precision of about 0.1%, at which they will provide constraints on new physics competitive with direct searches conducted at high energies at LHC. The experimental setup is installed in the ISOLDE experimental hall at CERN and received several $^{32}\mathrm{Ar}$ beamtimes over the past 8 years to reach this goal. The first one, in 2018, validated the principle of the measurement and the expected gain in sensitivity of the technique with respect to state of the art results. The world's third-best result on the angular correlation coefficient $a_{\beta\nu}$ was obtained in a single measurement of a pure Fermi decay. Following a full upgrade of the experimental setup and a second test beamtime in 2021, two experimental campaigns in 2024 and 2025 were successfully conducted, allowing to accumulate enough statistics to reach the required level of precision. A careful analysis of all sources of systematic errors has been carried out and no show-stopper has been identified yet. In this talk, we will present the final result of the WISArD measurement of the correlation parameter $a_{\beta\nu}$ from the 2024 and 2025 data takings and show how it compares with global constraints on exotic scalar currents.

The first spectroscopy of $^{78}$Ni [1] together with indications of shape coexistence just below the N=50 shell closure for $^{79}$Zn [2, 3] suggest that deformed intruder configurations could play a crucial role in low-energy structure properties in this region and towards the limits of the nuclear chart [4]. Such configurations are predicted to originate from multiparticle-multihole excitations [5] above the N=50 and Z=28 shell gaps pushed down in energy due to neutron-proton correlations which enhance quadrupole collectivity.

Because these intruder states involve many-particle excitations more difficult to describe theoretically, their predicted energies vary more drastically between models than for yrast states originating from ``normal'' configurations on which they tend to agree. Characterizing fully the properties of those states hence provides a good asset to benchmark microscopic models [1], or constrain effective shell model interactions [6].

This topic is the main objective of an experiment performed at the RIBF facility (RIKEN, Japan) [7] in order to identify and characterize, for the first time, 2p-1h intruder states in $^{83}$Ge. Neutron hole states in this N=51 nucleus were populated via neutron knockout reactions from the N=52 nucleus $^{84}$Ge which has about two neutrons in the $s_{1/2}d_{5/2}$ valence space above N=50. This direct reaction allows one to remove one of the neutrons from the quasi-full $g_{9/2}$ orbital below N=50 and selectively populate the $9/2^+$ intruder states in $^{83}$Ge based on a $\nu(g_{9/2})^{-1}(s_{1/2}d_{5/2})^{+2}$ configuration. In order to identify the populated states, gamma-rays from their in-flight decay were measured using the HiCARI Germanium array comprising six MINIBALL triple clusters, four Clovers, and two GRETINA-type detectors. In order to confirm the intruder nature of the states observed, parallel momentum distributions of reaction products were measured using the ZeroDegree spectrometer.

We propose to present here the identification of the main intruder candidate in $^{83}$Ge based on measurements including for the first time lifetime, spectroscopic factors, and parallel momentum distributions. These measurements will be compared with state-of-the-art Shell-Model calculations.

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Neutrinoless double beta decay (0νββ) is a rare nuclear process predicted by beyond-Standard Model theories, offering crucial insights into the nature of neutrinos and lepton number violation. A confirmed observation of 0νββ would establish the Majorana nature of neutrinos and provide constraints on their absolute mass scale. Among candidate isotopes, the decay of $^{136}$Xe to $^{136}$Ba is extensively studied in large-scale experiments such as EXO, KamLAND-Zen, nEXO, and PandaX. However, to date, experiments have only set lower limits on the decay lifetimes [1].

A significant challenge remains in the precise determination of nuclear matrix elements (NMEs), which introduce uncertainties in extracting neutrino properties from measured decay rates. Theoretical predictions of NMEs vary considerably [2], highlighting the need for improved nuclear structure data. This study investigates the nuclear structure of $^{136}$Ba, the daughter nucleus of $^{136}$Xe, through high-resolution gamma-ray spectroscopy using the FIPPS array at ILL. The focus is on low-spin states in $^{136}$Ba populated via the $^{135}$Ba(n,γ)$^{136}$Ba reaction, with particular emphasis on the characterization of low-spin 0$^{+}$ states. These states play a fundamental role in 0νββ decay transitions but remain incompletely understood.

The level scheme of $^{136}$Ba has been studied through $^{136}$Cs β decay and $^{136}$Ba(n,γ) reaction experiments. Although several (n,γ) studies have been conducted, the only published data dates back to 1969 [3]. More recently, a study of the $^{138}$Ba(p,t)$^{136}$Ba reaction [4] identified several previously unknown 0$^{+}$ states in $^{136}$Ba. The high statistics of this experiment will allow for a significant expansion of the existing data set.

The experimental setup consisted of 16 HPGe Clover detectors with anti-Compton shields, achieving an efficiency of 3.5 % at 1.4 MeV and an energy resolution of ~2 keV at 1.3 MeV. The experiment employed a thermal neutron beam from the ILL reactor with an intensity of ~10$^{7}$ n/s/cm² [5]. The results will highlight newly identified transitions and spin assignments for states up to 5 MeV in excitation energy. The coincidence method was used to assign new decay paths by analyzing gamma-gamma matrices, while spin assignments were determined through angular correlation analysis of coincident gamma rays, referencing existing literature on tentative spin values and mixing ratios.

Additionally, the findings will be compared with theoretical calculations to provide further insights into the nuclear structure of $^{136}$Ba. Lifetime measurements will be conducted to reduce uncertainties and provide new data. The vibrational and mixed-symmetry properties of $^{136}$Ba (N = 80) will also be explored to enhance the understanding of its collective dynamics. These results aim to reduce NME uncertainties, advance knowledge of 0νββ, and contribute to broader nuclear structure studies.

References:
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[3] W. Gelletly et al., Phys. Rev. 181, 1682 (1969).
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Zhou Yan¹, Xiaofei Yang¹, on behalf of PLASEN collaboration
¹School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China.

Nuclear charge radii and quadrupole moments are sensitive observables of nuclear deformation. Around neutron number N = 60, a region of deformation has been observed through measurements of nuclear ground-state properties of neutron-rich nuclei with Z = 37-41, including Rb, Sr, Y, Zr and Nb [1-3]. Among them, Rb is the lowest-Z element for which charge radii data beyond N = 60 are available, clearly exhibiting signatures of deformation. However, experimental data on nuclear radii and moments of neutron-rich Rb isotopes above N = 60 remain scarce, motivating further investigations [4,5].

Laser spectroscopy provides access to fundamental nuclear properties such as spins, magnetic dipole moments, electric quadrupole moments, and charge radii through measurements of hyperfine structure and isotope shifts in a nuclear-model-independent way [6]. Previous laser-spectroscopic studies have covered Rb isotopes from ⁷⁶Rb to ⁹⁸Rb, while the nuclear spin and other basic properties of ⁹⁹Rb have not yet been firmly established [4,5]. Recently, a high-resolution and high-sensitivity collinear resonance ionization laser spectroscopy system, PLASEN (Precision Laser Spectroscopy for Exotic Nuclei), has been developed for both off-line and on-line experiments, enabling systematic studies of exotic nuclei [7,8].

In this work, we report the first online collinear resonance ionization spectroscopy experiment performed with the PLASEN setup at the Beijing Radioactive Ion-beam Facility (BRIF). Hyperfine spectra of the $5s\ ^{2}\mathrm{S}_{1/2} → 5p\ ^{2}\mathrm{P}_{3/2}^\circ$ transition were measured for a series of Rb isotopes, including ⁹⁹Rb, with sufficient resolution to extract both magnetic dipole and electric quadrupole hyperfine constants. The extracted nuclear spin, moments, and charge radius of ⁹⁹Rb provide new information on nuclear deformation in this mass region.

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[7] Hu, H., Guo, Y. et al. Sci. Bull 70, 2721-2724 (2025).
[8] Y. F. Guo, Z. Yan, X. F. Yang et al., Chin. Phys. C 49 124002 (2025).

The hyperfine anomaly (HFA) originates from finite nuclear-size effects in the hyperfine interaction. It contains contributions from both the finite nuclear magnetization distribution, known as the Bohr-Weisskopf (BW) effect [1], and the finite nuclear charge distribution, known as the Breit-Rosenthal (BR) effect [2,3]. In heavy atoms, the differential BR contribution is expected to be negligible compared to the BW effect (10$^{-4}$ in the region of gold (Z=79)) [4]. In the Au isotopes considered here, the relative HFA is therefore expected to be dominated by the BW contribution. The gold isotopes are a particularly interesting case, since relative hyperfine anomalies between isotopes up to ≈ 10 % have been reported in this chain [5].

We report high-resolution Collinear Resonance Ionization Spectroscopy (CRIS) studies of neutron-deficient $^{181}$Au - $^{197}$Au isotopes, performed at the CRIS experiment at ISOLDE-CERN, using the 6s $^2$S$_{1/2}$ $\rightarrow$ 6p $^2$P$_{3/2}$ atomic transition. The precision on the atomic hyperfine coupling constants has been improved up to 2 orders of magnitude compared to previous studies [5-8]. This allowed us to investigate the electronic-state dependence of the extracted magnetic dipole moments, $\mu$. The magnetic moments measured independently from the lower and upper hyperfine A factors show a pronounced discrepancy, which becomes larger for isotopes with a larger $\mu$, suggesting a sizable hyperfine anomaly in the electronic states of Au. The present measurements confirm the spin assignments for $^{181}$Au-$^{183}$Au isotopes. Together, the spins and extracted g-factors help probe the underlying nuclear configuration and its evolution toward the lightest gold isotopes. These results also extend hyperfine-anomaly studies in gold to the 6p $^2$P$_{3/2}$ atomic level, providing a stringent benchmark for atomic many-body theory and nuclear-structure descriptions near Z = 82.

[1] A. Bohr and V. F. Weisskopf, Phys. Rev. 77, 94 (1950).

[2] J. E. Rosenthal and G. Breit, Phys. Rev. 41, 459 (1932).

[3] M. F. Crawford and A. K. Schawlow, Phys. Rev. 76, 1310 (1949).

[4] H. J. Rosenberg and H. H. Stroke, Phys. Rev. A 5, 1992 (1972).

[5] A.E. Barzakh, et. al, PRC 101, 034308 (2020)

[6] A.E. Barzakh, et. al, PRC 101, 064321 (2020)

[7] J. Cubiss, et. al, PRL 131, 202501 (2023)

[8] R.D. Harding, et. al, PRC 102, 024312 (2020)

The calcium isotopic chain, anchored by the doubly magic nuclei $^{40,48}$Ca, provides an important benchmark for studies focused on nuclear structure properties. In this region, nuclei in the vicinity of these shell closures exhibit predominantly single-particle behavior governed by the occupancy of the $f_{7/2}$ orbital, while the addition or removal of protons and neutrons drives a gradual evolution toward increased correlations and the emergence of collectivity toward the mid-shell region. The study of isotones in this mass region therefore offers direct insight into the role of proton-neutron interactions and the robustness of shell closures[1].

In this contribution, we present complementary laser spectroscopy studies probing nuclear properties in the vicinity of calcium. Within this context laser spectroscopy is a powerful probe of nuclear structure, enabling high-precision determination of electromagnetic moments, changes in mean-square charge radii, and nuclear spins. Collinear laser spectroscopy with fluorescence detection has been performed at the IGISOL facility on ionic transitions in vanadium isotopes (Z=23). Building on successful offline tests[4], this work has developed into an experimental campaign on radioactive isotopes in the mass range $A=46$ to $52$, providing new insights into a previously poorly explored isotopic chain. In parallel, results from the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE on neutron-rich argon isotopes (Z=18) are presented. These measurements extend previous studies[2,3] toward more neutron-rich systems, providing new data for $^{45,47,48}$Ar and probing the evolution of nuclear structure as protons are removed from the calcium core and neutrons populate the $pf$ orbitals.

In both experimental approaches, the studied isotopic chains extend beyond $N=28$, enabling a direct investigation of the persistence of the $N=28$ shell closure associated with the filling of the $\nu f_{7/2}$ orbital. Together, these studies provide a consistent picture of nuclear structure evolution in the calcium region, highlighting the interplay between single-particle behavior, shell evolution, and the emergence of collectivity as a function of proton number.

References:
[1] Á. Koszorús et al., Nuclear structure studies by collinear laser spectroscopy, Eur. Phys. J. A 60, 20 (2024).
[2] K. Blaum et al., Nuclear moments and charge radii of argon isotopes between the neutron-shell closures N=20 and N=28, Nucl. Phys. A 799, 30 (2008).
[3] A. Klein et al., Moments and mean square charge radii of short-lived argon isotopes, Nucl. Phys. A 607, 1 (1996).
[4] A. Karadimas et al., High precision measurements of the hyperfine structure of vanadium ions in the ultraviolet range, Sci. Rep. (2026).

Recent experimental innovations have driven major progress in nuclear fission research, a phenomenon fundamentally governed by the interplay of collective dynamics and quantum mechanical effects. Breakthroughs in inverse kinematics experiments alongside the development of complete detection setups now enable event-by-event reconstruction of the fission process with unprecedented precision. These advances provided access to new observables, including complete isotopic fission fragments distributions as a function of excitation energy, fission probabilities and manifold correlations between the properties of fission fragments and the neutrons and $\gamma$-rays they emit. Moreover, these techniques enable the study of unstable or short-lived fissioning systems, significantly expanding the range of nuclei which can be probed, and offering a path toward a comprehensive, potentially universal, description of the fission process across the nuclear chart. At the same time, recent results obtained with conventional approaches based on direct kinematics are providing increasingly accurate complementary information. Intense effort is invested to take advantage of the new findings for better constraining the theories which are being developed in parallel.

This presentation will review the main experimental advances achieved in recent years, including state of the art detection systems and modern analysis techniques. A selection of results that have reshaped our understanding of nuclear fission, or that continue to challenge long standing knowledge, will be presented. Current challenges and future opportunities for the field will also be discussed.

Nuclear fission remains one of the most complex scientific problems of our times. Complete information on fission products and the related fission spectrum plays a key role in applied nuclear technology and in basic science. Yet, accurate and precise measurements are often very complex and expensive, technically difficult to perform, or even impossible if the target nuclei are too short-lived, making accurate fission modeling especially important. Since the beginning of nuclear science, physics models of fission have been heavily data-driven in order to provide enough flexibility to match experimental measurements. At the same time, fundamental fission theory based on a fully quantum-mechanical description of the fission process has made spectacular progress in the past decade. Some of the knowledge gained is beginning to be translated into concrete guidelines or inputs for evaluations. In this presentation, I will discuss the state of the art of fundamental fission theory by reviewing the main accomplishments of the past decade and discussing some of the open questions in the field.

Nuclear fission is a complex quantum many-body process governed by the interplay between macroscopic liquid-drop properties and microscopic shell effects, which together determine the final fragment configuration. While early macroscopic approaches predicted predominantly symmetric mass splits for many systems, it is now well established that the quantum shell structure of the nascent fragments plays a decisive role in shaping the fission outcome. In particular, deformed shell gaps can favor asymmetric mass divisions, giving rise to the characteristic heavy-light fragment pattern observed across a broad range of fissioning nuclei. Recent high-precision measurements have identified a new region of asymmetric fission driven by shell effects in the light fragments, demonstrating that fragment-structure effects remain dominant even in previously unexplored areas of the nuclear chart.

To investigate this newly identified island of asymmetric fission, a dedicated experiment was performed at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany, employing inverse kinematics at relativistic energies with the state-of-the-art R$^3$B/SOFIA setup. We report measurements of fission-fragment charge distributions for 100 exotic fissioning systems, establishing a direct link between the neutron-deficient sub-lead region and the well-known actinide region. These data provide a comprehensive mapping of the asymmetric-fission island and deliver clear experimental evidence for the decisive role of the deformed proton shell at $Z=36$ in sub-lead fission.

In addition, we systematically investigated global odd-even staggering in the fission-fragment charge distributions as a function of the fissioning system. Our analysis demonstrates that shell structure in the fissioning nucleus itself contributes significantly to the observed staggering.

The interplay between macroscopic liquid-drop properties and microscopic effects represents a fundamental challenge in nuclear fission [1]. This competition can be probed through excitation-energy distributions, as experimental evidence shows a systematic attenuation of structure-dependent effects, thereby progressively revealing the underlying macroscopic component of the potential-energy surface. In this context, fission-fragment isotopic yields provide a sensitive observable for quantifying this evolution [2,3]. In the actinide region, fission at low energy is characteristically dominated by asymmetric mass splits driven by shell effects; however, increasing excitation energy reduces these structure-induced asymmetries and enhances the relative contribution of symmetric fission modes [4].

This specific approach is part of a systematic research campaign at GANIL designed to exploit transfer- and fusion-induced fission reactions in inverse kinematics [5-7]. A $^{238}$U beam at 5.88 AMeV impinged on four different targets ($^{27}$Al, $^{24}$Mg, $^{nat}$B and $^{9}$Be), populating a variety of actinides at low-to-moderate excitation energies. The use of inverse kinematics allows for the full isotopic identification (A, Z) and kinematic reconstruction of one of the fission fragments using the VAMOS++ spectrometer [8] in combination with the AGATA gamma-ray array [9]. Additionally, the use of SPIDER silicon telescope to detect the target-like recoil produced in the transfer reaction, enables an event-by-event characterisation of the fissioning system [6].

In this framework, the present study focuses on the evolution of fission-fragment isotopic yield distributions for selected actinides as a function of excitation energy. Furthermore, the impact of the incoming channel in the fission dynamics is investigated by comparing the fission-fragment production from different reactions leading to the same fissioning system.

References

[1] V. Strutinsky, Nuclear Physics A 95, 420–442 (1967).
[2] K.-H. Schmidt et al., Reports on Progress in Physics 81, 106301 (2018).
[3] A. N. Andreyev et al., Reports on Progress in Physics 81, 016301 (2017).
[4] K. Nishio et al., Phys. Rev. C 111, 044609 (2025).
[5] M. Caamaño et al., Phys. Rev. C 88, 024605 (2013).
[6] C. Rodríguez-Tajes et al., Phys. Rev. C 89, 024614 (2014).
[7] D. Ramos et al., Phys. Rev. C 97, 054612 (2018).
[8] M. Rejmund et al., Nuclear Instruments and Methods in Physics Research Section A 646, 184–191 (2011).
[9] E. Clément et al., Nuclear Instruments and Methods in Physics Research Section A 855, 1–12 (2017).

This study [1] explores the role of nucleon exchange for the generation of the fission fragment angular momenta. For a number of typical fission cases, samples of 10,000 shape evolutions are generated by Langevin simulation [2] and, subsequently, for each such evolution, the nucleon exchange transport theory previously developed for damped nuclear reactions [3] is used to obtain the development of the fragment spin-spin distribution within the Fokker-Planck transport framework. The characteristic evolution of both parallel and perpendicular spin components is discussed. A common feature is that the rotational modes fall out of equilibrium before scission when the temperature rises rapidly while the concurrent shrinking of the neck suppresses further exchange. A number of fission observables are extracted from the event ensembles: the distribution of the magnitude of the fragment spin and its orientation relative to the fission axis, as well as the correlation between the two spins and the distribution of their opening angle. The dependence of these observables on the mass asymmetry is also examined.

[1] J. Randrup, P. Nadtochy, C. Schmitt, K. Mazurek, Correlated fission fragment spin dynamics, Phys. Rev. C, 113 (2026) 044605
[2] G.D. Adeev, A.V. Karpov, P.N. Nadtochii, and D.V.Vanin, Multidimensional Stochastic Approach to the Fission Dynamics of Excited Nuclei, Phys. Part. Nucl. 36, 378 (2005)
[3] J. Randrup, Theory of transfer-induced transport in nuclear collisions, Nucl. Phys. A 327, 490 (1979).

Nuclear fission has shaped both our understanding of the atomic nucleus and many of the technologies that define the modern world. Nearly ninety years after its discovery, it continues to challenge fundamental theory while underpinning applications from national security and nonproliferation to energy production to astrophysics and nuclear medicine.

In this talk, I will focus on research areas where basic science questions and application-driven needs genuinely intersect. I will use concrete examples—fission cross sections, fragment angular distributions, fission product yields, prompt and beta-delayed emissions—to show how microscopic physics propagates through the nuclear data pipeline into the evaluated libraries used by most technologies. Along the way, I will “open the hood” on how these evaluations are produced and maintained in practice.

Finally, in an era of AI-driven workflows and large-scale optimization, I will revisit what we really mean by uncertainties and information content in both fundamental and applied fission research. Whether you are after sharper arguments for your favorite fission project, deeper insight into how the data behind your engineering tools are built, or new ways your measurements and calculations can have an impact, this presentation aims to give you something you can carry back into your work.

Despite the notorious advances in different theoretical models [1] and the development of new experimental setups that increase the access to the fission observables [2], there are still several phenomena in the fission process that are not reproduced with enough accuracy and whose origin is unclear. One of these occurrences is the so-called "Thorium Anomaly", which refers to the observed fission probabilities [3] and fission yields [4] around Thorium, that deviate from the behaviour of heavier actinides [5]. The scarce dataset and limited number of observables prevent so far to fully comprehend this sudden variation. The correlation between several parameters would allow to shed light on the current understanding.

Following the advantages of inverse-kinematics, a new experiment was conducted with the newly accelerated 232Th beam at Coulomb energies. Fusion, inelastic scattering and transfer reactions produced with a 12C target permitted to populate fissioning systems such as 232Th, 233Pa or 234U. The utilized experimental setup consisted on the VAMOS++ spectrometer [6], which was in charge of obtaining the isotopic identification of complete fission fragment distributions and their velocity vector. Moreover, the magnetic spectrometer was combined with a highly stripped silicon detector (PISTA), that allows the event-by-event identification of the fissioning system and the reconstruction of its excitation energy with high resolution [7] by measuring the target-like partner. The combination of both devices permits to systematically study the correlation between the fission observables for several nuclei, within the same configuration.

In this work, the elemental and isotopic fission fragment yields of 232Th will be presented. Having a simultaneous measurement of these yields with the excitation energy of the corresponding fissioning system, the evolution of these observables can also be investigated. The comparison between Thorium yields and heavier actinides gives more experimental insight into the understanding of the "Thorium anomaly".

References
[1] Schunck, N and Robledo, LM , Reports on Progress in Physics 79 (2016) 116301.
[2] Schmidt, K. H., Benlliure, J., & Junghans, A. R. (2001). Fission of nuclei far from stability. Nuclear Physics A, 693(1-2), 169-189.
[3] Back, B. B., Britt, H. C., Garrett, J. D., & Hansen, O. (1972). Subbarrier fission resonances in Th isotopes. Physical Review Letters, 28(26), 1707
[4] Berriman, A. C., Hinde, D. J., Jeung, D. Y., Dasgupta, M., Haba, H., Tanaka, T., ... & Williams, E. (2022). Energy dependence of p+ Th 232 fission mass distributions: Mass-asymmetric standard I and standard II modes, and multichance fission. Physical Review C, 105(6), 064614
[5] Schmidt, K. H., et al. (2024). Identifying and overcoming deficiencies of nuclear data on the fission of light actinides by use of the GEF code. Annals of Nuclear Energy, 208, 110784.
[6] M.Rejmund et al., Nuclear Instruments and Methods in Physics Research A 646 (2011) 184-191.
[7] Bégué - Guillou, L., Lemasson, A., Morfouace, P., Ramos, D., Taieb, J., Frankland, J. D., ... & Tonchev, A. P. (2026). Performance of the Particle-Identification Silicon-Telescope Array coupled with the VAMOS++ magnetic spectrometer. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1090, 171671.

As demonstrated by the extensive experimental and theoretical work conducted over the past decades, nuclear fission is a highly complex process. This complexity arises primarily from the interplay of diverse aspects of both reaction dynamics and nuclear structure, which together determine the observables measurable in the laboratory. Recent studies have shown that coincidences among multiple observables are crucial to unravel the intricacies of fission and ensure an unambiguous interpretation of the data. In this context, an innovative experimental setup was developed at GANIL, coupling for the first time the VAMOS++ heavy-ion spectrometer with the new-generation PARIS scintillator array. While VAMOS++ accurately identifies the mass and charge of the fission fragments, PARIS detects with unprecedented quality the coincident gamma rays over their full dynamical range, alongside information on coincident neutrons. This contribution presents the first experiment using PARIS@VAMOS, dedicated to fission induced by fusion and nucleon transfer in 238U + 9Be collisions around the barrier. A selection of results illustrates the performance of the setup in terms of efficiency, resolution, and sensitivity, highlighting the variety of topics that can be addressed. In particular, the so-called fission gamma bump and its highly probable connection to the Pygmy Dipole Resonance are demonstrated through calculations employing microscopic nuclear level densities and gamma strength functions [1]. This connection has a dual impact: it establishes the gamma bump as a relevant signature of post-scission dynamics, and it proposes fission as a new probe of soft dipole modes, complementary to conventional approaches.

References

[1] N. Kumar, Ch. Schmitt, M. Ciemała, et al., "First experimental isotopic mapping of the fission “γ-bump” and its connection to the Pygmy dipole resonance", Phys. Lett. B 878 (2026) 140506

Among the various processes of cosmic nucleosynthesis, the rapid neutron-capture process (r-process) plays a decisive role in the production of elements heavier than iron. A characteristic feature of the r-process abundance distribution is the so-called “rare-earth peak” around mass number A~160. The origin of this peak has been theoretically attributed to possible changes in nuclear shell structure and the presence of deformed shell gaps near N~100 [1-4]. Furthermore, while β-delayed neutron emission in the neutron-rich rare earth region is thought to play a key role in the formation of the A≈160 peak, experimental data in this mass region are scarce, and the detailed nature of the shell structure remains unclear.
We therefore have systematically investigated decay modes and structures in the neutron-rich rare-earth region using β-γ and isomer spectroscopy of A=150~160 Nd, Ce, Ba nuclei. The experiment was performed using RIBF facility in RIKEN Nishina Center. These neutron-rich nuclei were produced using in-flight fission of a 345 MeV/u $^{238}$U beam. Fission fragments were separated and transported by the BigRIPS and ZeroDegree spectrometer. Nuclei of interest were identified by measuring the time-of-flight and magnetic rigidity in the second stage of BigRIPS and by measuring the energy loss using the ion chamber at the final focal plane, F11. The secondary beam was implanted into an active stopper, WAS3Abi to perform β-γ spectroscopy using EURICA Ge cluster detector array. We obtained the results indicating β-delayed neutron emission in $^{158}$Nd for the first time.
In the presentation, the latest result of beta-gamma spectroscopy of $^{157,158}$Nd will be reported and its relevance to the rare-earth peak will be discussed.
This work is partially supported by JSPS KAKENHI Grant Number 26H01418.
[1] M.R. Mumpower, G.C. McLaughlin, R. Surman: Phys. Rev. C85, L021303 (2012).
[2] R. Surman, J. Engel, J. Bennett, and B. Meyer: Phys. Rev. Lett. 79, 1809 (1997).
[3] S. Shibagaki, T. Kajino, G. J. Mathews, S. Chiba, S. Nishimura, and G. Lorusso: Astrophys. J. 816, 1 (2015).
[4] S. Goriely, et al.: Phys. Rev. Lett. 111, 242502 (2013).

In the process of $\beta$-delayed fission ($\beta$DF), an excited state populated in the daughter nucleus after $\beta$ decay undergoes fission. The achievable excitation energy is limited by $Q_\beta$ value, which is typically $\lesssim$ 10 MeV. Therefore, $\beta$DF allows us to access so called low-energy fission, which is sensitive to nuclear structure, and to study its properties, such as fission fragment mass distributions, fission barriers, etc. [1,2]. Moreover, $\beta$DF plays an important role in the nucleosynthesis as it contributes to the termination and fission recycling in the $r$ process [3].

More than a decade ago, our collaboration started a unique experimental campaign dedicated to $\beta$DF studies at ISOLDE (CERN), in which several isotopes in the neutron-deficient lead region were measured [1,4-6]. In this contribution, our follow-up $\beta$DF experiments, which aimed at extending the studies to $^{178}$Au and to neutron-rich isotopes $^{230,232,234}$Ac, will be reported.

Isotope $^{178}$Au has two $\beta$-decaying states, which we studied individually by employing selective power of RILIS to obtain isomerically pure beams. Such measurement gives an additional possibility to explore spin dependence of fission, because of the strong spin selectivity of $\beta$ decay. No $\beta$DF events were observed for isotopes of interest despite collection of high statistics. Therefore, upper limits of $\beta$DF probabilities were determined. The limit for $^{230}$Ac was almost two orders of magnitude lower than the literature value [7], thus, questioning the observation of $\beta$DF for this isotope. The results will be discussed in the context of experimental systematics of $\beta$DF probabilities and partial half-lives.

[1] A. N. Andreyev, M. Huyse and P. Van Duppen, Rev. Mod. Phys. 85, 1541 (2013).
[2] A. N. Andreyev, K. Nishio, and K.-H. Schmidt, Rep. Prog. Phys. 81, 016301 (2018).
[3] S. Goriely et al., Phys. Rev. Lett. 111, 242502 (2013).
[4] L. Ghys et al., Phys. Rev. C 90, 041301(R) (2014).
[5] V. L. Truesdale et al., Phys. Rev. C 94, 034308 (2016).
[6] B. Andel et al., Phys. Rev. C 102, 014319 (2020).
[7] Y. Shuanggui et al., Eur. Phys. J A 10, 1 (2001).

One of the most important fission quantities is the fission barrier as it defines the fission cross sections. The most direct (and often the only) way to obtain fission barriers is to measure the fission probability as a function of the excitation energy of nuclei formed by transfer and inelastic scattering reactions. The measurement of the fission probability together with the probabilities for the de-excitation channels that compete with fission (e.g. gamma or multiple neutron emission) sets strong constraints on the description of the de-excitation process and can lead to a significant reduction of the uncertainty of the fission barrier parameters. However, the measurement of gamma or neutron-emission probabilities in standard experiments is very difficult due to the very low detection efficiencies for gamma rays and low-energy neutrons, and the intense background of gamma rays and neutrons emitted by the fission fragments. Moreover, so far, the decay probabilities have only been measured for nuclei close to the valley of stability due to the difficulty to produce and handle radioactive targets.
We are developing a project that studies for the first time fission in inverse kinematics at a heavy-ion storage ring. This allows one to measure with unrivalled precision the fission probability and the probabilities for all the de-excitation modes competing with fission of nuclei located far from stability.
In this talk, I will present our new methodology and the results of the first two experiments that we have successfully performed at the ESR storage ring of the GSI/FAIR facility in Darmstadt, Germany. In these experiments, we have achieved a significant breakthrough by measuring for the first time the fission, gamma-ray, neutron and even two- and three-neutron emission probabilities simultaneously. The measurement of all these probabilities enables the precise determination of fission barriers and other fundamental quantities, including particle transmission coefficients, gamma-ray strength functions, and nuclear level densities. All these quantities will be employed to infer (n,f), (n,gamma), (n,n'), (n,2n), and (n,3n) cross sections.

Angular momentum generation in nuclear fission remains one of the most intriguing and least understood aspects of the fission process. Although fission has been studied for more than eight decades, major questions persist regarding how angular momentum is generated at scission, how it is shared between the fragments and the orbital angular momentum, and how it correlates with excitation energy, deformation, and neutron emission. These questions are of central importance for our fundamental understanding of collective motion in nuclei and nuclear de-excitation processes.
In this talk, old and recent experimental and theoretical developments in the study of fission fragment angular momentum will be reviewed. Particular emphasis will be placed on modern approaches for extracting angular momentum from experimental observables. Special focus will be given to isomeric yield ratio measurements performed at the IGISOL facility using Penning trap techniques. Furthermore, theoretical descriptions of angular momentum generation and evolution in fission models such as GEF and FREYA will be discussed. Results obtained with different analysis frameworks, including the Manchester Spin Method and the TALYS-based Uppsala Spin Method, will also be presented and compared.
The talk will further address current challenges, including the role of fragment deformation and moments of inertia, the treatment of spin cut-off parameters, excitation energy sharing at scission, and the correlation between excitation energy and angular momentum. Finally, perspectives for future progress will be outlined, including the need for new high-precision measurements, improved theoretical descriptions of scission dynamics, and better constraints on angular momentum generation mechanisms in the different types of particle-induced fission.

Studies in heavy-ion induced fusion-fission process has established itself as one of the major branches of low and medium energy nuclear structure and reaction physics. A plethora of dynamical processes manifest through the fusion-fission of two atomic nuclei over a wide range of projectile energy. The process of fission followed by fusion of two heavy nuclei or survival of the Compound Nucleus (CN) against fission and formation of Evaporation Residues (ER) are deeply connected with various factors like, nuclear shell structure, target-projectile mass asymmetry, projectile energy, angular momentum distribution in the CN etc. Other than studying the dynamical effect associated with fusion and subsequent fission (or survival against fission) of heavy CN, there is also the long-standing desire to understand formation of very heavy or Super Heavy Elements (SHE). In this talk we plan to review the present status of heavy-ion induced fusion-fission processes at energies above the Coulomb Barrier. We would like to touch upon aspects of fission followed by complete and incomplete fusion and processes like fast and quasi-fission. We will be primarily drawing from our measurements carried out at Inter University Accelerator Centre, New Delhi using the Hybrid Recoil mass Analyser (HYRA) coupled with the TIFR 4π Sum-Spin spectrometer. We will summarise what we have learnt so far and what are the unresolved problems. Detailed analyses using both Statistical and Dynamical Model formalisms will be presented. We will also discuss the very important role of dissipative mechanism or nuclear viscosity in the survival of the CN against fission.
It is worth noting that the Giant Dipole Resonance (GDR) is another fascinating mode of nuclear collective motion. In this talk, we will make an effort to discuss the underlying fundamental aspects of correlated nuclear motion at finite temperature and angular momentum through two different but most prominent collective motions, fission and GDR. We will address the common link of viscosity and how far the collectivity exists, an evergreen question in GDR, but can also be invoked in fission physics.

As a source of neutrons within the nuclear chain reaction, prompt fission neutrons are of decisive importance for nuclear physics applications. Their average neutron multiplicity impacts the amount of neutrons available for further fissions, while their energy distribution impacts the probability for neutrons to escape the core of a nuclear reactor and do structural damages to the vessel. New high precision measurements of prompt fission neutron spectra (PFNS) and average prompt neutron multiplicity have been done at the WNR facility of the Los Alamos Neutron Science Center. The PFNS of the major actinides $^{239}$Pu, $^{235}$U and $^{238}$U were measured as a function of the incoming neutron energy by double time of flight for incoming neutron energies above 1 MeV with two different methods. While results of two methods will be shown, we will detail one type of measurement, performed with respect to the well known PFNS and average neutron multiplicity of $^{252}$Cf spontaneous fission.
The setup consisted of a high efficiency and fast-timing fission chamber coupled to the liquid scintillators array Chi-Nu or VENDETA (VErsatile Neutron DETector Array). Prompt fission neutron energies between 150 keV and 12 MeV can be measured, for incident neutron energies from 0.7 to 800 MeV. Average neutron multiplicities and mean neutron energies were extracted from the PFNS measurement as a function of the incoming neutron energy. Up to 25 MeV of incoming neutron energies, relative uncertainties are below 0.5% on the average neutron multiplicity and below 0.8% on the mean energy. The energy range measured and the level of precision achieved allow us to observe the opening of alternative fission channels, such as second chance fission. Beyond the need for evaluated nuclear data libraries and nuclear applications, this level of precision also provide constrains on fission models such as GEF and CGMF, and on partial fission cross sections. The experimental method will be detailed and the results will be compared to existing data, evaluations and fission models for discussion.

Nuclear fission results in two excited fragments which de-excite very quickly via the emission of prompt neutrons and gamma rays. These emissions can be detected and contain a wealth of information about the fission process itself, especially from the correlations between the emitted particles. The particular difficulty in studying fission is that this emission occurs from two moving sources at almost the same point in space and at the same time. There are many experimental approaches available to help understand the fission process [1][2][3], and of particular relevance is the role of angular momentum. In this presentation the focus will be on the technique of high-resolution gamma ray coincidence spectroscopy both within a particular fragment and between fragment partners. The information that can be extracted will be reviewed, along with the limitations of the approach, and future promising avenues of research will be outlined.

[1] S. Cannarozzo, et al., Phys. Rev. C 111, L031601 (2025)
[2] M. Travar et al. Phys. Lett. B 817 136293 (2021)
[3] J.N. Wilson et al., Nature 590 566 (2021)

Multi-humped fission barriers, as they occur in the actinide region, give rise to fission isomerism. Such barrier shapes can be described within various theoretical models. Experimentally measured observables of nuclear fission isomers—such as the half-life, excitation energy of the fission isomer, kinetic energy of the fission fragments, and the isomer-to-ground-state population ratio—allow for testing theoretical predictions and verifying the role of shell effects in nuclear structure.
Studies of the fission isomer properties of 240,242Am were performed at the IGISOL facility at the JYFL Accelerator Laboratory, University of Jyväskylä, Finland. Fission isomeric states were populated via deuteron-induced fusion–evaporation reactions on a

242

Pu target. The decays of the fission isomers were detected using silicon detectors calibrated with a 252Cf fission source.
The measurements provided detailed information on kinetic energy spectra, total kinetic energies, and mass distributions for 240,242Am. A new method was proposed to derive post-neutron-emission mass distributions, as well as proton- and neutron-number multiplicity distributions of the fission fragments, from their kinetic energy distributions. In addition, the emission probabilities of prompt neutrons in the fission process were extracted. Using data for the 252Cf fission isomer as a reference, the validity of the method was verified.

The obtained results for 240,242Am and 252Cf are consistent with GEF model predictions and previous measurements. These findings contribute to a better understanding of shell effects and fission barrier structures in the actinide region.

The JYFL Accelerator Laboratory (JYFL-ACCLAB) is one of the leading stable beam facilities in Europe, conducting world class research on basic natural phenomena. Presently the laboratory hosts three accelerators with a variety of ion sources and innovative instrumentation for fundamental research, ion-beam based materials physics and applications. The current main research facilities includes the on-line isotope separator IGISOL producing low-energy radioactive ion beams (RIBs) which are coupled to ion/atom traps and laser systems, two recoil separators (gas-filled, RITU, and vacuum mode, MARA) with novel multi-detector systems for low cross-section in-beam and stopped-beam spectroscopy experiments, infrastructure for a variety of ion beam analysis methods and a RADiation Effects Facility, RADEF. At the end of 2026, the laboratory will install a new Tandetron accelerator to further our applied physics programme.

The IGISOL facility explores ground- and isomeric state properties of nuclei via mass spectrometry as well as laser and decay spectroscopy for nuclear structure and astrophysics, and fundamental interactions. Recent developments include combining laser resonance ionization with sensitive mass separation and detection resulting in almost background free measurements at the N = Z line. New international projects MORA and SEASON are data taking. New developments include novel laser- and sympathetic cooling techniques for ultra-high precision measurements, coupling the MR-TOF mass spectrometer for collinear laser spectroscopy as well as a decay spectroscopy station.

The nuclear spectroscopy team, with state-of-the-art detector systems coupled with recoil separators, have produced a wealth of in-beam and decay studies, probing structures and phenomena in proton drip-line nuclei and heavy elements produced via heavy-ion fusion-evaporation reactions. The JUROGAM3 array of Ge detectors can be moved with ease between the target positions of both separators. Ongoing efforts towards realizing a gas cell at the focal plane of MARA to deliver exotic beams to a new low-energy branch continues.

In this presentation I will present an overview of the status of the facility and will highlight the current research activities as well as some of the new projects foreseen in the near future.

The neutron-rich cadmium isotopes, with two protons below the Z = 50 shell closure, constitute a unique laboratory for investigating the interplay between single-particle structure and collective excitations in the vicinity of the doubly magic $^{132}$Sn [1,2]. The evolution of nuclear structure in this region is governed by the gradual filling of neutron orbitals between the N = 50 and N = 82 shell closures, and cadmium isotopes have long served as textbook examples in discussions of vibrational collectivity [3,4]. However, as the neutron number increases towards N = 82, the persistence of vibrational behavior is challenged by the growing importance of pairing effects and seniority-driven structures near closed shells [4,5]. Spectroscopic information on $^{122}$Cd (N = 74), lying eight neutrons below the N = 82 shell closure, is therefore directly relevant to understanding the structural transition from a collective to a more seniority-dominated regime. Such data also provide useful benchmarks for shell-model calculations in this mass region [6,7].

In this work, the excited-state structure of $^{122}$Cd was investigated through beta-delayed gamma spectroscopy following the decay of $^{122}$Ag. The experiment was performed at the IGISOL facility of the University of Jyväskylä Accelerator Laboratory, Finland [8,9]. Isobarically pure beams were obtained by mass separation and Penning-trap purification with JYFLTRAP [9], and the collected activity was implanted at a dedicated decay station. The detection setup comprised three clover HPGe detectors, two coaxial HPGe detectors, and a plastic beta scintillator, operated in saturation mode with no tape movement during the counting cycle, allowing continuous accumulation of activity.

An extended decay scheme for the $^{122}$Ag → $^{122}$Cd decay was constructed on the basis of gamma-ray energies, relative intensities, and gamma-gamma coincidence relations. Spin-parity assignments are proposed for selected excited states populated in the beta decay, based on the observed coincidence topology and intensity-balance considerations. The resulting feeding pattern is discussed in terms of the dominant excitation mechanism, vibrational versus seniority-type, and confronted with available shell-model calculations for neutron-rich cadmium nuclei [6,7]. The new spectroscopic data provide important constraints on the effective interactions used in large-scale shell-model calculations near $^{132}$Sn [2,6].

[1] Y. X. Luo, J. O. Rasmussen, A. Gelberg et al., “New high-spin level schemes and excitation modes of 117,118,119,120,122Cd,” Nucl. Phys. A 784 (2007) 1–19. https://doi.org/10.1016/j.nuclphysa.2011.11.001

[2] K. L. Jones, A. S. Adekola, D. W. Bardayan et al., “The magic nature of 132Sn explored through the single-particle states of 133Sn,” Nature 465 (2010) 454–457. https://doi.org/10.1038/nature09048

[3] J. C. Batchelder, J. L. Wood, P. E. Garrett et al., “Low-lying collective states in 120Cd populated by β decay of 120Ag: Breakdown of the anharmonic vibrator model at the three-phonon level,” Phys. Rev. C 80 (2009) 054318. https://doi.org/10.1103/PhysRevC.80.054318

[4] P. E. Garrett, K. L. Green, J. L. Wood, “Breakdown of vibrational motion in the isotopes 110–116Cd,” Phys. Rev. C 78 (2008) 044307. https://doi.org/10.1103/PhysRevC.78.044307

[5] T. Kautzsch, W. B. Walters, M. Hannawald et al., “Evidence for collective behavior in the neutron-rich isotopes 126,128,130Cd,” Eur. Phys. J. A 9 (2000) 201–204. https://doi.org/10.1007/s100500070038

[6] L. Coraggio, A. Covello, A. Gargano, N. Itaco, “Similarity of nuclear structure in the 132Sn and 208Pb regions: proton-neutron multiplets,” Phys. Rev. C 80 (2009) 021305(R). https://doi.org/10.1103/PhysRevC.80.021305

[7] B. Maheshwari, H. Abu Kassim, N. Yusof, A. K. Jain, “Parallel tale of seniority isomers in 130Cd and 206Hg: Testing the robustness of magic numbers,” Nucl. Phys. A 992 (2019) 121619. https://doi.org/10.1016/j.nuclphysa.2019.121619

[8] I. D. Moore, T. Eronen, D. Gorelov et al., “Towards commissioning the new IGISOL-4 facility,” Nucl. Instrum. Methods Phys. Res. B 317 (2013) 208–213. https://doi.org/10.1016/j.nimb.2013.06.036

[9] T. Eronen, V. S. Kolhinen, V.-V. Elomaa et al., “JYFLTRAP: a Penning trap for precision mass spectroscopy and isobaric purification,” Eur. Phys. J. A 48 (2012) 46. https://doi.org/10.1140/epja/i2012-12046-1

The Cosmic Neutrino Background (C$\nu$B), a relic from the Big Bang predicted to consist of non-relativistic neutrinos at a present temperature of $\sim$1.95 K, has never been directly detected. Its experimental observation would provide the first direct evidence for non-relativistic neutrinos and open new avenues for probing neutrino masses and early-Universe cosmology. Among the most promising candidate nuclei for relic neutrino capture detection are $^{151}$Sm and $^{171}$Tm, owing to their low $\beta^-$ decay $Q$ values ($Q_{\beta^-} \approx 76.6 \pm 0.5$ keV and $96.5 \pm 1.0$ keV, respectively [1]) and favorable nuclear-structure properties [2, 3]. However, the currently adopted $Q$ values, derived from indirect mass-link chains and historical $\beta^-$ endpoint measurements [4], carry uncertainties at the $\sim$1 keV level. As shown by Kostensalo et al. [3], this is the dominant source of uncertainty in the predicted relic neutrino capture cross-sections, especially for $^{171}$Tm, translating into $\sim$10% variations in the estimated target mass required for detection experiments.

To overcome this limitation, we aim to measure the $Q_{\beta^-}$ values of $^{151}$Sm and $^{171}$Tm directly using the phase-imaging ion-cyclotron-resonance (PI-ICR) technique [5, 6] at the JYFLTRAP double Penning trap mass spectrometer at the IGISOL facility in the University of Jyväskylä, in June 2026. The PI-ICR method determines the cyclotron frequency ratio between the daughter and parent ions with a relative precision of $\Delta Q/M \sim 10^{-9}$, corresponding to a $Q$-value uncertainty of $\sim$100 eV for these heavy nuclei, an order-of-magnitude improvement over current values. The parent isotopes will be produced via light-ion induced fusion-evaporation reactions ($^{\text{nat}}$Nd($\alpha$,$xn$)$^{151}$Sm at 30 MeV and $^{\text{nat}}$Er($^3$He,$xn$)$^{171}$Tm at 24 MeV), while the stable daughter isobars $^{151}$Eu and $^{171}$Yb from a local discharge ion source will serve as references for the measurements. Advanced ion-cleaning methods, Ramsey-type excitations, and interleaved measurement cycles will be employed to suppress systematic effects arising from magnetic-field fluctuations, trap imperfections, and ion-ion interactions. The obtained $Q$ values will provide essential nuclear input data for next-generation C$\nu$B detection experiments.

References

[1] O. Mikulenko, Y. Cheipesh, V. Cheianov, A. Boyarsky, Eur. Phys. J. A 59, 216 (2023).

[2] V. Brdar, R. Plestid, N. Rocco, Phys. Rev. C 105, 045501 (2022).

[3] J. Kostensalo, J. Kotila, J. Suhonen, Phys. Lett. B 840, 137894 (2023).

[4] W. J. Huang et al., Chin. Phys. C 45, 030002 (2021).

[5] D. A. Nesterenko et al., Eur. Phys. J. A 54, 216 (2018).

[6] D. A. Nesterenko et al., Eur. Phys. J. A 57, 302 (2021).

The region between the strongly deformed nuclei around the $Z \sim 40$, $N \sim 60$ mass region and the spherical Sn chain represents a rich testing ground for nuclear structure models, probing shell evolution and the interplay between single-particle and collective degrees of freedom, as well as phenomena such as shape coexistence. In this context nuclear magnetic dipole moments are sensitive probes of the single-particle nature of nuclear configurations, while electric quadrupole moments reflect the degree of nuclear deformation. The changes in mean square charge radii further provide information on the evolution of nuclear size across an isotopic chain. Laser spectroscopy experiments enable the extraction of all these observables, along with nuclear spins, for ground and isomeric states in a nuclear model-independent manner from the measurement of isotope shifts and hyperfine structures of the atomic spectra [1].

In this contribution, the results of first collinear laser spectroscopy studies performed on a series of neutron-deficient Rh isotopes will be presented. These isotopes are expected to exhibit a structural evolution from emerging collectivity in the mid-shell region towards sphericity approaching $^{95}$Rh at $N=50$, as evidenced by observations in the neighboring Ru and Pd isotopic chains [2,3].
The isotopes of interest were produced at the IGISOL facility, University of Jyväskylä, utilizing the ion guide method [4], essential for the successful production of refractory elements such as Rh. The isotope shifts and hyperfine structure parameters of ground and isomeric states between $^{95}$Rh and $^{104}$Rh were subsequently measured via collinear fluorescence laser spectroscopy[5]. These measurements provide the first determination of mean-square charge radii and nuclear moments of ground and isomeric states across this isotopic chain. Additionally, these results will contribute to resolve ambiguities in the spin assignments of $^{95m}$Rh, $^{98m,g}$Rh, $^{100m}$Rh, and $^{102}$Rh. The extracted nuclear observables will be compared with theoretical models describing single-particle configurations and shape transitions in the region.

[1] Yang, X., et al., Progress in Particle and Nuclear Physics 129 (2020) 104005.
[2] Geldhof, S., et al., Physical review letters 128.15 (2022): 152501.
[3] Maas, B., et al., Physical review letters 135.20 (2025): 202501.
[4] Moore, I. D., et al., Hyperfine interactions 223.1 (2014): 17-62.
[5] Koszorús, Á., et al., The European Physical Journal A 60.1 (2024): 20.

$\beta$-decay can be used as a simple and selective approach to populate certain nuclear excited states and study them. If the imbalance between proton and neutron number is large, levels in the daughter nucleus can be populated above the particle separation energy, leading to single or multi-particle emission. These new decay channels provide an opportunity to study nuclear structure at high excitation energy [1], nuclear astrophysics processes [2] and fundamental symmetries of the weak interaction.

Detecting all the particles emitted after $\beta$-decay with a good efficiency becomes necessary to obtain the full decay path information. It is in this context that the Regina Cube for Multiple Particles (RCMP), ancillary detector for the GRIFFIN HPGe $\gamma$-ray spectrometer at TRIUMF [3] has been developed to explore $\beta$-decay at the proton drip line. RCMP is a set of six double-sided silicon strip detectors (DSSD) arranged in a cubic geometry, allowing to measure the energy of charged particles emitted after $\beta$-decay. Added to GRIFFIN, this state-of-the-art setup is the most effective to date in order to perform this type of study.

This work presents the first results obtained with this experimental setup, where the full $\beta$-delayed spectroscopy of $^{20}$Mg and $^{21}$Mg has been achieved with the highest statistical yield measured to date, providing a significative contribution to the understanding of nuclear structure and astrophysics processes at the proton drip line in the A $\sim$ 20 region.

[1] M. V. Lund et al. “Systematic trends in beta-delayed particle emitting nuclei: The case of βpα emission from $^{21}$Mg”. In: Phys. Lett. B 750 (Nov. 2015)

[2] M. V. Lund et al. “Beta-delayed proton emission from $^{20}$Mg”. In: Eur. Phys. J. A 52.10 (Oct. 2016)

[3] A. B. Garnsworthy et al. “The GRIFFIN facility for Decay-Spectroscopy studies at TRIUMF-ISAC”. In: Nucl. Instrum. Methods Phys. Res., Sect. A 918 (Feb. 2019)

The limit of existence on the neutron-deficient side of the nuclide chart is determined by the proton separation energy. In his 1960 work [1], V. Goldansky postulated the probability of simultaneous emission of two protons, known today as two-proton (2p) radioactivity, for even-Z isotopes beyond the proton drip line. It is an extremely rare phenomenon and to this day only four 2p emitters were observed: $^{45}$Fe [2 - 5], $^{48}$Ni [6, 7], $^{54}$Zn [8 - 10] and $^{67}$Kr [11]. However, with the exception of $^{45}$Fe, the global statistics till now is by far insufficient to even attempt at understanding this decay mode, preventing to draw any conclusions about decay mechanism or insight into competition between $\beta^+$ and 2p decay.

At the beginning of 2025, a series of measurements of the decays of $^{48}$Ni, $^{54}$Zn, and $^{45}$Fe were conducted at the Facility for Rare Isotope Beams (FRIB) [12] at Michigan State University with the Warsaw OTPC (Optical Time Projection Chamber) detector. The ions of interest were produced in fragmentation of a primary $^{58}$Ni beam on a carbon target, separated by the Advanced Rare Isotope Separator (ARIS) spectrometer [13], transmitted down the beamline and implanted into the OTPC detector, where subsequent decays were registered.

These measurements allow for the study of the structure of these even-Z nuclei beyond the proton drip-line, in particular the p-p correlation pattern across the Z=28 shell closure. While the analysis of the data is in progress, preliminary results can already provide valuable insight into decay properties and will be presented.

[1] V. Goldansky, Nuclear Physics 19 (1960): 482-495.
[2] M. Pfützner et al., EPJ A 14.3 (2002): 279-285.
[3] J. Giovinazzo et al., PRL 89.10 (2002): 102501.
[4] C. Dossat et al., PRC (2005): 054315.
[5] K. Miernik et al., PRL 99.19 (2007): 192501.
[6] M. Pomorski et al., PRC 90.1 (2014): 014311.
[7] A. Ortega Moral et al., PRC 112.6 (2025): L061302.
[8] B. Blank et al., PRL 94.23 (2005): 232501.
[9] P. Ascher et al., PRL 107.10 (2011): 102502.
[10] A. Kubiela et al., PRC 113.2 (2026): 024310.
[11] T. Goigoux et al., PRL 117.16 (2016): 162501.
[12] T. Glasmacher et al., Nuclear Physics News 27.2 (2017): 28-33
[13] M. Hausmann et al, NIM B 317 (2013): 349-353.

The G-22-00111 experiment was performed at the FRS facility at GSI within the EXPERT programme [1] being a part of Super-FRS Experiment Collaboration [2]. The experiment was aimed at the investigation of very proton-rich light systems, including the search for the four-proton decay of $^7$C. In the experiment, secondary $^9$C and $^7$Be beams, produced from a primary $^{12}$C beam with energy 860 MeV/nucleon, were transported to physical beryllium secondary target.

Performance of the EXPERT tracking setup, with particular emphasis on the FOOT single-sided silicon strip detectors [3] will be discussed. Eight FOOT detectors, arranged in four pairs, were installed downstream of the secondary target and used for detection and tracking of protons and light fragment emitted from decays of nuclei of interest. The setup also included ALPIDE pixel detectors, while the standard FRS detector system provided event-by-event identification of beam particles and light fragment. The second half of the FRS was tuned to register $^3$He and $^4$He fragments.

Preliminary analysis of the FOOT data demonstrates the capability of the setup to detect proton hits and to reconstruct multi-track events originating from a common reaction vertex. As a benchmark channel for the analysis, we use the population of $^{6}$Be (from the fragmentation of the $^7$Be secondary beam on the beryllium target). The decay of $^6$Be to $^4$He and two protons leads to a well known three-body final state [4], in which two proton tracks and helium fragment track can be measured in the FOOT detectors. The standard FRS detector system provides event-by-event beam identification and additional constraints on the reaction channel.

The reconstruction of 2p+$^4$He events from $^6$Be will be used to develop and validate the analysis procedure, including track and vertex reconstruction, particle identification, and decay-energy reconstruction. This methodology will then be extended to more complex nuclear systems, in particular to the search for $^7$C candidates decaying into $^3$He+4p.

References:
[1] H. Geissel et al., EXPERT studies at the Super-FRS spectrometer, in: Exotic Nuclei, World Scientific, 2015.
[2] J. Äystö et al., Experimental program of the Super-FRS collaboration at FAIR and developments of related instrumentation, Nucl. Instrum. Methods Phys. Res. B 376 (2016) 111–115.
[3] G. Silvestre et al., Test of a prototype Microstrip Silicon Detector for the FOOT experiment, J. Phys.: Conf. Ser. 2374, 012065 (2022)
[4] V. Chudoba et al., Three-body correlations in direct reactions: Example of $^6$Be populated in the (p,n) reaction, Phys. Rev. C 98, 054612 (2018)

Investigating exotic nuclei far from the valley of stability provides crucial insights into nuclear structure and the underlying forces that shape it. The experimental determination of atomic and nuclear properties such as atomic energy levels, ionization potentials, electromagnetic moments, trends in mean-square charge radii, and isotope shifts for nuclei in the region of heavy actinides by laser spectroscopy is difficult. The main challenges are low production rates at accelerator facilities and unfavorable half-lives of the fusion products. This necessitates the use of highly efficient and selective laser spectroscopy techniques. At GSI-FAIR in Darmstadt, Germany, the RAdiation Detected Resonance Ionization Spectroscopy (RADRIS) has been successfully used to study aforementioned properties in $^{245,246,248-250,254}$Fm and $^{252-255}$No [1-3].
The employed detection of laser-ionized atoms via their $\alpha$-decay becomes impractical for nuclei with half-lives on the order of several tens of hours using a single detector. Thus, a more versatile design with eight detectors was developed to increase the method's reach towards longer-lived nuclei. The upgraded detector setup was used in a recent measurement campaign to investigate isotope shifts the element californium. The isotopic chain of $^{240,241,242,244,246}$Cf was studied using laser spectroscopy, revealing trends in the changes of mean-square charge radii. This complements previous investigations of $^{249-253}$Cf at the RISIKO mass separator of the Johannes Gutenberg-University Mainz, Germany [4].

[1] M. Laatiaoui et al., Nature 538, 495–498 (2016)
[2] J. Warbinek et al., Nature 634, 1075–1079 (2024)
[3] S. Raeder, et al., Physical Review Letters, 120(23) 232503 (2018)
[4] F. Weber et al., Atoms, 10(2), 51 (2022)

Gold and platinum nuclei near the $N$ = 104 mid-shell, including $^{182}$Au and $^{182}$Pt, have drawn significant attention owing to the rapid evolution of ground-state deformation relative to heavier isotopes. In even-even platinum isotopes in particular, experimental evidence points to the coexistence of distinct configurations, commonly associated with weakly oblate and more deformed prolate shapes [1,2]. These structural features have been extensively studied using a range of experimental techniques, including laser spectroscopy [3] and $\beta$-delayed $\gamma$-ray spectroscopy [4]. The latter approach often provides access to excited levels in the daughter nucleus up to relatively high excitation energies. Since $\beta$ decay is sensitive to changes in nuclear structure, $\beta$-decay feeding patterns and log $ft$ values provide insight into shape coexistence and configuration mixing in the daughter nucleus.

In this contribution, we present results of a detailed $\gamma$-ray spectroscopy of the $^{182}$Pt level structure populated in the electron capture/$\beta^+$ decay of $^{182}$Au. The experiment was performed at the ISOLDE facility, where a high-purity $^{182}$Au beam was produced using element-selective laser ionisation and mass separation. The implanted activity was measured at the ISOLDE Decay Station (IDS) [5] equipped with four HPGe Clover detectors and an array of silicon PIN diodes. Transitions known from the previous $\beta$-decay study [4] were confirmed, and the level scheme of $^{182}$Pt was significantly expanded [6]. Log $ft$ values for decays populating the first three $2^+$ states in $^{182}$Pt indicate mixing between different band structures. Moreover, a notably strong $\beta$-decay feeding intensity to 4$^+$ levels was observed, which is inconsistent with the second-forbidden non-unique $\beta$ decay expected from the currently assigned $(2^+)$ ground state of $^{182}$Au [7]. We consider several possible explanations, including a reassignment of the $^{182}$Au ground state, the existence of a new isomeric state, and the impact of the Pandemonium effect.

[1] K. Heyde and J. L. Wood, Rev. Mod. Phys. 83, 1467 (2011).
[2] P. E. Garrett, M. Zielińska and E. Clément, Prog. Part. Nucl. Phys 124, 103931 (2022).
[3] J. G. Cubiss et al., Phys. Rev. Lett. 131, 202501 (2023).
[4] P. M. Davidson et al., Nucl. Phys. A 657, 219 (1999).
[5] ISOLDE Decay Station website. https://isolde-ids.web.cern.ch
[6] J. Mišt et al., Phys. Rev. C. 112, 024328 (2025).
[7] R. D. Harding et al., Phys. Rev. C 102, 024312 (2020).

This study presents a major advancement in understanding the nuclear structure of superheavy nuclei through spectroscopy of the high-K 8- isomer in 254No. Leveraging the enhanced sensitivity of the GABRIELA detector array at JINR (Dubna), γ-ray emissions and internal conversion electrons (ICE) were observed simultaneously for the first time. The results reveal a new 4+ state at 1203 keV, identified as the spin partner of the previously known 3+ state. Together, they form a Gallagher-Moskowski doublet; their 216 keV energy difference provides the first experimental measurement of spin splitting between two-quasiproton states in the actinide region. Furthermore, analysis of the ICE spectrum uncovered an intense electric monopole (E0) strength, indicating a second 0+ state at 884 keV excitation energy. These findings are well-reproduced by a new extension of the Shell Model (DNO-SM(VAP)), offering a vital benchmark for validating beyond-mean-field theoretical models in heavy deformed nuclei. All experimental results and comparison with theoretical model will be presented.

Nuclear deformation has been a topic of interest for many decades. While most nuclei can be described using only quadrupole deformation, recent experimental results [1, 2], in agreement with theoretical predictions [3, 4], indicate that a more exotic type of deformation, namely octupole deformation, is needed to best describe nuclei in certain regions of the nuclear chart. In particular, the region of most enhanced octupole collectivity can be observed in the actinides around Z = 88 and N = 134.

In this framework and more generally for the study of heavy nuclei, a new decay station named SEASON (Spectroscopy Electron Alpha in Silicon bOx couNter) has been developed at CEA-Irfu. The online commissioning of the instrument was performed at the IGISOL facility of the Accelerator Laboratory of the University of Jyväskylä, Finland, in February 2026. SEASON is designed to meet the constraints of a high-energy-resolution decay station and an efficient counter for laser spectroscopy of heavy and superheavy nuclei. The detection system is made of 7 DSSD (Double-sided Silicon Stripped Detector) for the detection of alpha particles and conversion electrons, and is coupled with 2 HPGe (High Purity Germanium) detectors for the gamma-rays.

At IGISOL [5], a proton beam of energy 65 MeV induced fusion-evaporation reactions on a $^{232}$Th target, producing, among other neutron-deficient actinide isotopes, $^{225}$Pa, which decays to $^{221}$Ac by alpha emission. This reaction, previously studied at IGISOL with a different setup [6], allowed for the evaluation of SEASON performances and the better quantification of conversion electron factors, which are crucial to perform spin-parity assignments of the states. The resulting level scheme will provide insights into the nature of the deformation of $^{221}$Ac.

First, the detection characteristics of SEASON, including energy resolution and efficiency, will be presented. Then, preliminary online commissioning results will be shown. These results will provide precision on the limits of the static octupole deformation in the neutron-deficient actinide region, illustrating the potential of what could be achieved in the future with SEASON at IGISOL and later at the S3-LEB facility, in GANIL, of which SEASON will be an integral part.

References
(1) Gaffney, L. P. et al. Nature 2013, 497, 199–204.
(2) Verstraelen, E.; Teigelhöfer, A.; Ryssens, W.; Ames, F.; Barzakh, A.; Bender, M.; Ferrer, R.; Goriely, S.; Heenen, P. - H.; Huyse, M.; Kunz, P.; Lassen, J.; Manea, V.; Raeder, S.; Van Duppen,P. Physical Review C 2019, 100, 044321.
(3) Butler, P. A. Journal of Physics G: Nuclear and Particle Physics 2016, 43, 073002.
(4) Cao, Y.; Agbemava, S. E.; Afanasjev, A. V.; Nazarewicz, W.; Olsen, E. Physical Review C 2020, 102, 024311.
(5) Moore, I. D.; Dendooven, P.; Ärje, J. Hyperfine Interactions 2014, 223, 17–62.
(6) Rey-herme, E. et al. Physical Review C 2023, 108, 014304.

Studies of superheavy nuclei provide important insights into nuclear structure at the limit of stability and allow for stringent tests of state-of-the-art nuclear models [1]. These nuclei may exhibit $K$-isomers, providing a unique probe of single-particle structure [2].

One prominent example is the $K^{\pi}=8^{-}$ isomer in $^{254}$No. Despite numerous $\gamma$-spectroscopic studies, the quasiparticle configuration remained for many years unresolved [3-5], largely because earlier experiments weakly populated the isomer’s rotational bands. This has prevented reliable $M1/E2$ branching ratio and $g$-factor measurements, leaving configuration assignments to rely mainly on indirect spectroscopic evidence and theoretical calculations [5].

We have performed complementary experiments using in-gas-jet laser ionization spectroscopy of the $K^{\pi}=8^{-}$ isomer in $^{254}$No ($T_{1/2}=259(7)\,\text{ms}$ [5]) with the JetRIS apparatus at the focal plane of the SHIP velocity filter at GSI, Darmstadt. The hyperfine spectroscopy of this short-lived isomeric state enabled the determination of the magnetic dipole moment, electric quadrupole moment, and isomer shift in a nuclear-model-independent way. The subsequent determination of the isomer's $g$-factor allows us to determine the quasiparticle configuration unambiguously.

[1] M. Block et al., Prog. Part. Nucl. Phys. 116 (2021) 103834.
[2] P. Walker and Z. Podolyák, Phys. World 34 (2021) 29.
[3] R.-D. Herzberg et al., Nature 442 (2006) 896.
[4] F. P. Heßberger, arXiv:2309.10468 (2023).
[5] S. G. Wahid et al., Phys. Rev. C 111 (2025) 034320.

Excited states with high $K$ quantum numbers provide valuable information on the underlying nuclear structure. Due to the conservation of the $K$ quantum number in deformed nuclei, transitions requiring large changes in $K$ are strongly hindered, and thus those excited states exist as isomers [1,2]. Of special interest are superheavy nuclei, where the high-$K$ states are significantly stable against fission [3,4]. This enables access to nuclei whose ground states would otherwise be too short-lived to be experimentally studied [5].

$K$ isomers are spread over in nobelium ($Z=102$) and rutherfordium ($Z=104$) isotopes; however, in the heavier elements, only two $\alpha$-decaying cases have been observed [$^{270}$Ds ($Z=110$) and $^{266}$Hs ($Z=108$)] [2]. Only recently, at TASCA, a strong indication of a $K$-isomeric state was observed in a seaborgium ($Z=106$) isotope, i.e., in $^{259}$Sg [6].

Inspired by this observation [6], all experimental data on seaborgium isotopes accumulated at SHIP during 2003-2009 were revisited. In this talk we will present the results from the reanalysis of those experimental data.

References
[1] P. Walker and G. Dracoulis, Nature 399, 35 (1999).
[2] D. Ackermann, S. Antalic and F. P. Heßberger, Eur. Phys. J. Spec. Top. 233, 1017 (2024).
[3] F. R. Xu et al., Phys. Rev. Lett. 92, 252501 (2004).
[4] J. Khuyagbaatar, Eur. Phys. J. A 58, 243 (2022).
[5] J. Khuyagbaatar, P. Mosat, et al., Phys. Rev. Lett. 134, 022501 (2025).
[6] P. Mosat, J. Khuyagbaatar, et al., Phys. Rev. Lett. 134, 232501 (2025).

In the transfermium region (Z $\geq 100$), spontaneous fission (SF) is a prominent decay mode, often competing with alpha and beta decay. However, experimental measurements remain challenging for most super-heavy nuclei (SHN) due to their low production cross-section. Stability against SF is governed by the fission barrier, which is strongly influenced by shell effects [2]. Hence, studies of mendelevium isotopes, located one proton beyond the closed Z=100 shell, could provide important information on the effect of single particle orbitals on SF.

An experiment was performed at Argonne National Laboratory (ANL) to study the alpha-decay properties of the neutron-deficient $^{244,245}$Md, aiming to resolve discrepancies between two previous studies. These earlier experiments, carried out at the TASCA separator of GSI [3] and at the BGS separator of LBNL [4], measured the isotopes using fusion-evaporation reactions. However, they reported two different assignments for the alpha-decaying states of $^{244}$Md and $^{245}$Md.

In the ANL experiment, neutron-deficient Md isotopes were produced via the fusion-evaporation channels of the reaction $^{40}$Ar+$^{209}$Bi, and separated using the Fragment Mass Analyser (FMA) of the ATLAS facility [1]. The M/Q separation performed at the FMA, combined with the focal plane detection system, enables decay spectroscopy studies of exotic nuclei even at low production rates.

The results of alpha decay analysis have been reported elsewhere [5]. However, in addition to these, multiple SF events were observed tens of microseconds after recoil implantation. SF events were also observed in [3] during measurements of $^{244}$Md, but a definitive isotopic assignment was not made for these events. The present work will focus on the analysis of the fission events observed at ANL and on the investigation of their possible origin.

[1] C. N. Davis and J. D. Larson, NIM-B 40/41, 1224-1228 (1989)

[2] J. Khuyagbaatar, Eur. Phys. J. A 55, 134 (2019)

[3] J. Khuyagbaatar et al., Phys. Rev. Let. 125, 142504 (2020)

[4] J. L. Pore et al., Phys. Rev. Let. 124, 252502 (2020)

[5] S. Kumar et al., Acta Phys. Pol. B Proc. Suppl. 19, 1-A24 (2026)

When studying the decay properties of heavy elements isolated using recoil separators the nuclei of interest are typically implanted into a highly ''pixelated'' Double-sided Silicon Strip Detector (DSSD). Upstream of the implantation DSSD, a tunnel-like arrangement of silicon detectors is used to measure internal conversion electrons (ICE) emitted from the decay of excited nuclear states. They form a crucial element in determining the electromagnetic character of the observed decay, hence the quantum nature of the states. Surrounding the silicon detectors are high-purity germanium detectors that measure X-rays and $\gamma$-ray quanta. An example of such a system is GABRIELA [1].

Alpha particles emitted at backward angles (''escape alphas'') that are observed in the tunnel share their total energy between the implantation and tunnel detectors. This phenomenon can mask real $\alpha$-ICE (implantation-tunnel) coincidences. One such example are the conversion electrons emitted from the decay of excited states in $^{251}$Fm, populated via the $\alpha$-decay of $^{255}$No. These can be contaminated by a low energy escape alpha background from the more intensely populated $^{254}$No [2] (when using the $^{48}$Ca + $^{208}$Pb reaction channels).

Reverse injected Silicon detectors have been used to distinguish protons from deuterons [3] and different incident heavy ions [4] using analogue electronics. An analysis of the pulse shapes of the digitised output from a current sensitive preamplifier was performed for the first time for atomic clusters in reference [5]. Two methods were developed: the simplest plotted the maximum current as a function of the charge (integral of the current). The second, more robust, method used the averaged current signals of each cluster type as a basis function with which to classify individual pulses based on a $\chi^2$ analysis. The simplified method has also been applied to distiguish Z$\leq$ 2 ions down to $\sim$3 MeV [6] using a 500 $\mu$m NTD-Si (crystal orientation $<$1 1 1$>$) and a dual output (I and Q) preamplifier [7].

Pulse shape analysis has been performed to compare conversion electrons from $^{133}$Ba and $^{207}$Bi sources with alpha particles from a mixed $^{239}$Pu, $^{241}$Am and $^{244}$Cm source after passage through a degrader foil to obtain alpha particles in the 0 - 1 MeV energy range. The $\chi^2$ and single parametric methods of reference [5] have been applied with success and the results will be briefly presented since they will feature in a publication already. While the $\chi^2$ template matching method is an extremely powerful off-line analysis method it is not efficiently implemented in an online DAQ context. In this talk I will focus on results from our effort to perform a multi-parametric discrimination of ICE from escape alphas using Neural Networks. These networks are small enough to be implementable online providing a non-destructive metric of "electroness" to flag a large percentage of the background.

\vspace{0.5cm}

\textbf{References}\newline [1] R. Chakma, \textit{et al.}, European Physics Journal A \textbf{56} (2020) 245.
\newline [2] K. Rezynkina, Ph.D Thesis, Université Paris Saclay, 2016:\ ~~~https://theses.hal.science/tel-01394373
\newline [3] C.A.J. Ammerlaan, \textit{et al.}, Nucl. Instr. and Meth. \textbf{22} (1963) 189.
\newline [4] M. Mutterer, \textit{et al.}, IEEE Trans. Nucl. Sci. \textbf{47} (2000) 756.
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\newline [6] J.A. Due\~nas, \textit{et al.}, Nucl. Instr. and Meth. A \textbf{676} (2012) 70.
\newline [7] H. Hamrita, \textit{et al.}, Nucl. Instr. and Meth. A \textbf{531} (2004) 607.

Most of the heaviest nuclei synthesized in recent decades were obtained through the use of fusion-evaporation reactions. This mechanism tends to produce mainly neutron-deficient nuclei due to neutron evaporation and the limited available choices of beam-target combinations. Moreover, production cross-sections for the heaviest elements are particularly small, e.g. 0.5 pb at most for the discovery of 294Og [1]. Consequently, Multi-Nucleon Transfer (MNT) reactions are expected to be a complementary mechanism to fusion-evaporation. Indeed, this mechanism is well suited to produce neutron-rich heavy ions with relatively high cross sections at forward angles of the order of µbarns according to the theory [2].
An experiment was performed at Argonne National Laboratory in 2023 to study MNT reactions using a 136Xe beam on a 238U target with detection of the reaction products at forward angles. The setup consisted of the Gammasphere germanium array [3] to perform a prompt γ-ray spectroscopy and the AGFA gas-filled separator 4 to separate the MNT products from the unreacted beam. A decay station for decay spectroscopy studies was also installed at the focal plane, consisting of a DSSD, a MWPC and silicon detectors in a tunnel configuration surrounded by four Clover germanium detectors.
The successful identification and cross-section extraction of few-nucleon transfer channels were achieved for data collected at a beam energy below the calculated barrier. The findings of this analysis and their interpretation as a signature of the dynamical deformation of the colliding nuclei will be presented in this talk.

References:
[1] Yu. Ts. Oganessian et al. Synthesis of the isotopes of elements 118 and 116 in the 249 Cf and 245 Cm + 48 Ca fusion reactions, Phys. Rev. C 74, 044602 (2006).
[2] V.I. Zagrebaev and W. Greiner. Cross sections for the production of superheavy nuclei. Nuclear Physics A, 944:257–307, (2015). Special Issue on Superheavy Elements.
[3 I-Yang Lee. The GAMMASPHERE. Nuclear Physics A, 520:245-258, (1990).
[4] B. B. Back. The AGFA and AIRIS separators at ATLAS. EPJ Web Conf. 163, 00003 (2017)

The measurement of lifetimes of excited nuclear levels is an important technique for probing the details of internal nuclear structure. The electromagnetic transition rates extracted can be linked to the composition of the wavefunctions of the initial and final states involved, and also to nuclear shape (via β$_2$ deformation), thereby allowing stringent tests of nuclear models. In recent years, arrays of LaBr$_3$(Ce) detectors with sub-nanosecond timing capabilities have enabled precision electromagnetic transition rate determinations in some of the most exotic radionuclides. This talk will describe some recent measurements in A~100 nuclei and discuss the physics insights that have been obtained from interpreting the results

More than 60 years ago, Macfarlane and Siivola proposed that the proximity of the doubly magic nucleus ¹⁰⁰Sn would strongly enhance the α decay of N≈Z tellurium isotopes, with the ¹⁰⁰Sn+α system behaving as a molecule-like configuration [1]. This conjecture frames a central question in the physics of α radioactivity, how and where the α particle preforms before emission, for which the decay of a nucleus into a doubly magic daughter is the most stringent testing ground [2]. The search for ¹⁰⁴Te α decay was pursued over the last two decades through studies of the heavier tellurium and xenon isotopes and their decay chains [3–6], culminating in the 2018 identification of the ¹⁰⁸Xe→¹⁰⁴Te→¹⁰⁰Sn chain, which placed only an upper limit of T1/2 (¹⁰⁴Te) < 18 ns [7].
Reported here is a definitive measurement of the ¹⁰⁴Te lifetime. The degree of decay enhancement observed in this work exceeds existing model predictions [8–11], raising the question of whether current α-emission models are complete. ¹⁰⁴Te occupies a singular position on the chart of nuclides: it has equal numbers of protons and neutrons and can α decay directly to doubly magic ¹⁰⁰Sn. I will discuss the experimental efforts that led to this discovery, place it in a theoretical context, and examine the models that attempt to explain the enhancement of ¹⁰⁴Te α-particle emission.

This research was partly sponsored by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contract No. DE-FG02-96ER40983 (UTK). This work was also sponsored by the Stewardship Science Academic Alliances program through DOE Awards No. DE-NA0004068.

References
[1] R. D. Macfarlane and A. Siivola, "New region of alpha radioactivity," Phys. Rev. Lett. 14, 114 (1965). 10.1103/PhysRevLett.14.114
[2] H. J. Mang, "Calculation of α-transition probabilities," Phys. Rev. 119, 1069 (1960). 10.1103/PhysRev.119.1069
[3] D. Schardt et al., "Alpha decay studies of tellurium, iodine, xenon, and cesium isotopes," Nucl. Phys. A 326, 65 (1979).
[4] R. D. Page et al., "Alpha radioactivity above ¹⁰⁰Sn including the decay of ¹⁰⁸I," Phys. Rev. C 49, 3312 (1994). 10.1103/PhysRevC.49.3312
[5] D. Seweryniak et al., "Population of the 168-keV (g₇/₂) excited state in ¹⁰³Sn in the α decay of ¹⁰⁷Te," Phys. Rev. C 66, 051307(R) (2002). 10.1103/PhysRevC.66.051307
[6] S. N. Liddick et al., "Discovery of ¹⁰⁹Xe and ¹⁰⁵Te: superallowed α decay near doubly magic ¹⁰⁰Sn," Phys. Rev. Lett. 97, 082501 (2006). 10.1103/PhysRevLett.97.082501
[7] K. Auranen et al., "Superallowed α decay to doubly magic ¹⁰⁰Sn," Phys. Rev. Lett. 121, 182501 (2018). 10.1103/PhysRevLett.121.182501
[8] P. Mohr, "α-nucleus potentials, α-decay half-lives, and shell closures for superheavy nuclei" / ¹⁰⁴Te prediction, Eur. Phys. J. A 31, 23 (2007). 10.1140/epja/i2006-10168-7
[9] S. Yang, C. Xu, G. Röpke et al., "α decay to a doubly magic core in the quartetting wave function approach," Phys. Rev. C 101, 024316 (2020). 10.1103/PhysRevC.101.024316
[10] R. M. Clark et al., "Enhancement of α-particle formation near ¹⁰⁰Sn," Phys. Rev. C 101, 034313 (2020). 10.1103/PhysRevC.101.034313
[11] F. Mercier et al., "Microscopic description of the self-conjugate ¹⁰⁸Xe and ¹⁰⁴Te α-decay chain," Phys. Rev. C 102, 011301(R) (2020). 10.1103/PhysRevC.102.011301
[12] I. C. Cox, R. Grzywacz et al., "Direct observation of the superallowed α-decay of ¹⁰⁴Te," Nature (2026). 10.1038/s41586-026-10581-w

Coulomb excitation of the even–even isotopes $^{130}$Sn and $^{134}$Sn was performed at the HIE-ISOLDE facility using post-accelerated radioactive ion beams at 4.4 MeV/u impinging on various targets. De-exciting γ rays were detected with the high-efficiency Miniball spectrometer in coincidence with scattered particles. The extracted B(E2) transition strengths resolve the long-standing discrepancy between experimental and theoretical estimates of quadrupole collectivity in $^{130}$Sn and $^{134}$Sn. The newly determined spectroscopic quadrupole moments are consistent with zero, emphasizing the near-spherical character of nuclei surrounding the $^{132}$Sn core. These findings establish stringent benchmarks for large-scale shell-model calculations employing realistic interactions and elucidate the evolution of quadrupole collectivity in the neutron-rich Z=50 region. The results confirm an enhanced B(E2) strength in $^{132}$Sn relative to its neighboring isotopes, providing firm experimental evidence for a local maximum of collectivity at the doubly magic nucleus.

Supported by the German BMBF 05P21PKFN9 and 05P21RDCI2 and European Union’s Horizon Europe Framework research and innovation programme under grant agreement no. 101057511

Cultural heritage conservation relies more and more on the support of scientific analysis, in particular by using techniques that are non-invasive. This is a fundamental characteristic when dealing with unique artworks of the utmost historical and/or artistic importance.
In order to study the structure of the binding of a book, in particular when the book cannot be easily opened without damaging it, the cover needs to be taken apart. Such invasive method is not applicable in the case of precious and unique historical books. An alternative and, most importantly, non-invasive method to understand the structure of the binding without dismounting the cover is to exploit imaging by means of X-rays, which are highly penetrating and don’t cause any damage. Namely, computed tomography (CT), in particular micro-CT, can be applied in such studies.
Micro-CT can then be used to study the book structure, in particular the spine, as support for conservation work, to provide an insight before physically touching the book and intervening on it.
In this pilot study, the method was used to support conservation work on the prayer book of Mary Stuart, Queen of Scots. It is a delicate, illuminated manuscript on vellum, written in Latin and French, made first for the Abbess of Fontevraud, who donated it to Mary Stuart, her niece. Following a rebinding in the late 18th/early 19th century, pages were misplaced, some are missing, and it was no longer possible to open the book to more than about 30 degrees without damage to the binding and the pages.
The results of the analysis conducted in the framework of the book conservation will be discussed.

Operational efficiency at accelerator facilities could be significantly improved through the automation of beam production and delivery, thereby increasing scientific output and nuclear data production. In this presentation, a practical path toward deploying artificial intelligence and machine learning (AI/ML) tools for the optimization of stable and radioactive ion beam production and transport at the ATLAS accelerator facility is described, with emphasis placed on the tools developed for the nuCARIBU source. The approach taken toward safe automation will be shared, including the operational safeguards by which reliable performance is supported. Lessons learned during deployment will be highlighted, and synergistic beam-tuning automation efforts at ATLAS will be discussed. How these tools and lessons could be adapted to other facilities, including university-based accelerator laboratories, will also be considered, with the aim of supporting and accelerating ongoing automation efforts across the community.

This work was supported by the Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357 and under Award No. DE-FOA-0002875. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.

The study of three-nucleon (3N) systems serves as a fundamental testing ground for our understanding of nuclear interactions, bridging the gap between basic nucleon-nucleon (NN) potentials and the complex dynamics of many-body nuclei. Experiments performed at intermediate beam energies reveal that various dynamical ingredients, such as the three-nucleon force (3NF) and Coulomb force, play an important role in accurately describing observables. High-precision measurements of differential cross sections for elastic scattering and breakup reactions, as well as spin observables like vector and tensor analyzing powers enable rigorous testing of theoretical calculations based on various approaches [1–4] to modeling interactions in three-nucleon systems. Additionally, studies of the $^1$H(d, pp)n reaction at relatively low energies are crucial for testing predictions of Chiral Effective Field Theory [5].
The presentation will focus on the effects of the 3NF and the Coulomb force on the differential cross section of the $dp$ breakup reaction, measured over a wide range of energies between 50 and 170 MeV/nucleon [6–10]. Furthermore, information about ongoing projects conducted at the Cyclotron Center Bronowice, PAS, Kraków, Poland, will also be discussed.

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[7] I. Skwira-Chalot et al., Few-Body Syst. 65 (2024) 24.
[8] W. Parol et al., Phys. Rev. C 102 (2020) 054002.
[9] A. Łobejko et al., Few-Body Syst. 65 (2024) 36.
[10] B. Kłos et al., Phys. Rev. C 101 (2020) 044001.

For six decades, Jerzy Dudek has made seminal contributions to the study of the rich variety of shapes and symmetries in atomic nuclei at the extremes of angular momentum, excitation energy, deformation, isospin and mass. Throughout this incredibly exciting period, the interplay between experiment and theory has been an exhilarating demonstration of the power of the scientific method, with fascinating, and often unexpected, aspects of atomic nuclei being revealed by increasingly sensitive detector systems, coupled with bold predictions from new highly sophisticated theoretical calculations. Jerzy, and his collaborators, have been deeply involved, and usually at the vanguard, at every twist and turn on this long and winding road. This presentation will reflect on a selection of these topics and his significant contributions, along with a brief glimpse towards some of the extraordinary physics opportunities of the future.