Speaker
Description
Simple systems near the doubly-magic shell closures offer optimal scenarios for assessing the accuracy of shell-model predictions. While near the stability path, the predictions are consistent with experimental data; the nuclide properties change as we move away towards the neutron-rich nuclide. In this context, a comprehensive understanding of nuclear structure in the immediate vicinity of the doubly-magic nucleus $^{132}$Sn is crucial before making projections regarding nuclear properties in more neutron-rich isotopes.
Some of the theoretical models predict that in the region to the southeast of $^{132}$Sn, nuclear structure plays a significant role in influencing the competition between neutron and $\gamma$-ray emissions in the decay of neutron-unbound states. The results of our recent experiments at ISOLDE Decay Station (IDS) confirm this and point to a significant contribution from the electromagnetic decay of unbound excited states, which are populated in the $\beta$-decay of isotopes $^{133,134,135}$In [1,2]
Moreover, these nuclei and the competition between neutron and $\gamma$-ray emissions that occurs during their $\beta$ decay are also significant within the context of the astrophysical
r-process.
Emission of delayed neutrons in $^{128}$Sn was not observed in previous studies, but it cannot be ruled out. The existing experimental information about excited states populated in
$\beta$-decay comes from the decay of the ground state (3$^+$) and the isomeric state (8$^-$) of the isotope $^{128}$In [3].
The recent mass measurement [4] allowed the observation of a new 16$^{+}$ isomeric state in $^{128}$Sn, and the observed $\beta$-delayed $\gamma$ transitions corresponding to its decay indicate the necessity for a revision of the current decay scheme. Furthermore, the excitation energy of the new 16$^{+}$ isomeric state enables the feeding of unbound levels in the $^{128}$Sn nucleus.
Excited states in $^{128}$Sn were investigated through the $\beta$-decay of $^{128}$In at the IDS. The implementation of $\beta$-$\gamma$ and $\gamma$-$\gamma$ coincidences in the preliminary analysis of $^{128}$In data revealed six previously unknown transitions and two excited levels in $^{128}$Sn.
[1] M. Piersa, A. Korgul et al., Phys. Rev. C 99, 024304 (2019).
[2] M. Piersa-Siłkowska, A. Korgul et al., Phys. Rev. C 104, 044328 (2021).
[3] B. Fogelberg and P. Carle, Nucl. Phys. A 323, 205 (1979).
[4] D.A. Nesterenko et al., Phys. Lett. B 808, 135642 (2020).
