Speaker
Description
The $r$-process sensitivity studies have identified nuclei southeast of the doubly magic $Z=50$ $N=82$ $^{132}$Sn as crucial in calculating the $r$-process nucleosynthesis for almost all astrophysical environments. This is due to the robustness of the $N=82$ and $Z=50$ shell closures, which causes a dramatic discontinuity in proton and neutron separation energy. This feature forces the $r$-process sequence of neutron capture to follow a path aligned with the $N=82$ shell closure and a sharp turn-off towards more neutron-rich nuclei at $Z=50$. This also results in the unique sensitivity of the $r$-process to nuclear properties of the nuclei below $^{132}$Sn, even though the $^{132}$Sn itself is not directly involved.
Using the time-of-flight technique, we measured the beta-delayed neutron emission of $r$-process waiting point $^{132}$Cd. From our large-scale shell model (LSSM) calculation using the N$^3$LO interaction [Z.Y. Xu et al., Phys. Rev. Lett. 131, 022501 (2023)], we suggest the decay is dominated by the transformation of a neutron in the $g_{7/2}$ orbital, deep below the Fermi surface, into a proton in the $g_{9/2}$ orbital. We compare the beta-decay half-lives and neutron branching ratios of nuclei with $Z<50$ and $N\geq82$ obtained with our LSSM with those of leading ``global" models such as Finite-Range Droplet Model (FRDM). Our calculations match known half-lives and neutron branching ratios well and suggest that current leading models overestimate the yet-to-be-measured half-lives. Our model, backed by the $^{132}$Cd decay data presented here, offers robust predictive power for nuclei of astrophysical interest such as $r$-process waiting points.
| Contribution category | Experiment |
|---|---|
| Presenter status | Faculty/Staff |