Zakopane 2026 Conference on Nuclear Physics

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].

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[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