Speaker
Description
The nuclei in the south of 208Pb, which is so called “blank spot” in the nuclear chart, remain experimentally less explored than other neutron-rich regions because of the difficulty in producing and identifying these nuclei with sufficient yield. In particular, the Re isotopes with Z=75 provide a sensitive testing ground for studying the evolution of nuclear shape. With increasing neutron number, these nuclei are expected to evolve from well-deformed prolate structures toward non-axial and oblate configurations. Previous studies of neighboring Re isotopes have revealed rotational structures, quasiparticle excitations, and long-lived isomeric states, indicating strong competition between intrinsic configurations and collective deformation [1,2]. The nucleus 192Re, with N=117, is especially important because it lies close to the predicted prolate-oblate transitional region [3]. However, prior to the present study, no spectroscopic information was available on its high-spin structure and the known data were mainly restricted to the low-spin isomeric state [4].
Recent developments in multi-nucleon transfer reactions with heavy-ion beams have opened new possibilities for accessing neutron-rich nuclei around A≈190, which are difficult to populate by conventional fusion-evaporation, fission, or fragmentation techniques [5]. In the present work, excited states in 192Re were populated using a multi-nucleon transfer reaction induced by a 136Xe beam at 7 MeV/nucleon incident on a 198Pt target at GANIL. Prompt and delayed γ rays from 192Re were measured using the AGATA tracking array and the second arm CATLIFE spectrometer [6] coupled to EXOGAM HPGe detectors, while projectile-like fragments were identified event-by-event with the VAMOS++ spectrometer. The 192Re reaction channel was selected using projectile-fragment identification, kinematic correlations, total kinetic energy loss selection, and confirmed with known isomer decay.
Using prompt-delayed and prompt-prompt γ-γ coincidence techniques, excited states above the known isomeric structure of 192Re were established for the first time, making it the most neutron-rich rhenium nucleus for which the excited states above an isomer have been measured . The resulting level structure provides the first experimental information on the high-spin excitation pattern of this nucleus. The observed sequence suggests the development of collective behavior above the isomeric state, while comparison with lighter neighboring odd-odd Re isotopes indicates changes in the underlying intrinsic configuration with increasing neutron number. The theoretical calculation using cranking-relativistic DFT using PC-PK1 covariant density functional and shell model-like approach was carried out to interpret the experimental result. These results extend the spectroscopy of 192Re into the high-spin regime and provide new constraints on the evolution of deformation and quasiparticle structure in neutron-rich Re isotopes below 208Pb.
References
[1] D. A. Matters et al., Phys. Rev. C 96, 014318 (2017).
[2] S. J. Steer et al., Phys. Rev. C 84, 044313 (2011).
[3] K. Sahrma et al., Phys. Rev. C 111, L031301 (2025).
[4] H. Watanabe et al., Phys. Lett. B 814, 136088 (2021).
[5] Y. X. Watanabe et al., Phys. Rev. Lett. 115, 172503 (2015).
[6] Y. Son et al., Nucl. Instr. And Meth. B 540, 234 (2023).