Speaker
Description
Abstract
The region around the doubly-magic $^{78}\mathrm{Ni}$ ($Z = 28$ and $N = 50$) is crucial for nuclear structure studies since it provides an ideal testing ground to investigate shell evolution and the interplay between single-particle and collective effects. Currently, many experimental and theoretical efforts are dedicated to investigate this region of the nuclear chart [1-3], aiming to understand the robustness of nuclear shells far from stability and the emergence of collective effects when nucleons are added. The interaction among valence nucleons may be capable of attenuating the magic nature of a nucleus very close to shell closures [4]. From this perspective, isotopes of Ge ($Z = 32$) are of interest to understand the evolution of the $N = 50$ gap.
In a recent experimental campaign, neutron-rich Ge isotopes were investigated via beta-decay spectroscopy of neutron-rich Ga using the ISOLDE Decay Station. Ga beams were produced at the ISOLDE facility at CERN by fission on a thick $\mathrm{UC}_x$ target by fast neutrons produced in a proton-to-neutron converter by the PSB proton beam. High production yields were achieved for isotopes such as $^{83-85}\mathrm{Ga}$, populating $^{82-85}\mathrm{Ge}$ through $\beta$-decay and $\beta$-delayed neutron emission.
The high yields and the 40 High Purity Germanium crystals in clover configuration at the ISOLDE Decay Station enabled the identification of new transitions and levels and provide the capability to perform angular correlation measurements for spin-parity assignments. In addition, two $\mathrm{LaBr}_3\mathrm{(Ce)}$ and three fast beta detectors were used to perform lifetime measurements of excited states in the sub-nanosecond range via fast-timing techniques.
In this contribution the extended level schemes of $^{85,84}\mathrm{Ge}$ and lifetime results will be presented. Furthermore, a theoretical interpretation of the nuclear structure of $^{84}\mathrm{Ge}$ based on the Projected Generator Coordinate Method using the Gogny D1S force and quadrupolar constraints with cranked HFB wavefunctions [5, 6] will be shown and compared to the experimental results.
References
[1] R. Yokoyama et al., $\beta$-delayed neutron emissions from N > 50 gallium isotopes, Physical Review C 108 (2023) 064307.
[2] K. Sieja et al., Laboratory versus intrinsic description of nonaxial nuclei above doubly magic $^{\mathrm{78}}$Ni, Physical Review C 88 (2013) 034327.
[3] C. Delafosse et al., Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the $^{\mathrm{78}}$Ni Region: A Hint from Lifetime Measurements, Physical Review Letters 121 (2018) 192502.
[4] A. Huck et al., Beta decay of the new isotopes $^{\mathrm{52}}$K, $^{\mathrm{52}}$Ca, and $^{\mathrm{52}}$Sc; a test of the shell model far from stability, Physical Review C 31 (1985) 2226.
[5] J. Berger et al., Microscopic analysis of collective dynamics in low energy fission, Nuclear Physics A 428 (1984) 23–36.
[6] L. M. Robledo et al., Mean field and beyond description of nuclear structure with the Gogny force: a review, Journal of Physics G: Nuclear and Particle Physics 46 (2018) 013001.