Speaker
Description
Simple systems in the proximity of the doubly-magic shell closures constitute the best cases for testing the predictive power of shell-model calculations. In this context, understanding of the nuclear structure in the closest vicinity of the doubly-magic $^{132}$Sn is essential before making extrapolations of the nuclear properties towards more neutron-rich nuclei. Recently, it was indicated that in the region southeast of $^{132}$Sn nuclear structure effects affect the neutron versus $\gamma$ ray competition in the decay of neutron-unbound states [1]. $\beta$-decay studies of neutron-rich indium isotopes, $^{135}$In, $^{134}$In and $^{133}$In, provide excellent conditions to investigate such effects since their decays are characterized by large energy windows for the population of neutron-unbound states ($Q_{\beta n} >$ 10 MeV). Consequently, states in $\beta$, $\beta n$ and even $\beta2n$ daughters of indium isotopes can be investigated simultaneously. These nuclei and the $n$-$\gamma$ competition following their $\beta$ decay are also relevant in the framework of the astrophysical r-process since $^{135}$In is a so-called waiting point [2].
Excited states in $^{135}$Sn, $^{134}$Sn, $^{133}$Sn and $^{132}$Sn were investigated via $\beta$ decay of $^{135}$In, $^{134}$In and $^{133}$In at ISOLDE Decay Station. Isomer-selective ionization using the Resonance Ionization Laser Ion Source enabled the $\beta$ decays of $^{133g}$In (I$^{\pi}$=9/2$^+$) and $^{133m}$In (I$^{\pi}$=1/2$^-$) to be studied independently for the first time [3]. Owing to the large spin difference of those two $\beta$-decaying states, it is possible to investigate separately the lower- and higher-spin states in the daughter $^{133}$Sn and therefore to probe independently different single-particle transitions relevant in the $^{132}$Sn region. States having neutron-hole nature were identified in $^{133}$Sn at energies exceeding neutron-separation energy up to 3.7 MeV [3]. Due to centrifugal barrier hindering the neutron from leaving the nucleus ($\ell=4$ or $5$), the contribution of electromagnetic decay of those unbound states was found to be significant. The same phenomenon was identified for a new neutron-unbound state observed in $^{134}$Sn. In addition to the previously known transitions following the $\beta$ decay of $^{134}$In [4, 5], we firmly assigned 11 $\gamma$ transitions to the decay of $^{134}$In based on parent half-life and $\gamma$-$\gamma$ coincidences with the known $\gamma$ rays depopulating states in $^{134}$Sn, $^{133}$Sn and $^{132}$Sn. $\beta$ and $\beta 2n$ decay branches of $^{134}$In have been observed for the first time. Preliminary results of the first $\beta$-decay studies of $^{135}$In will be presented. A comprehensive description of excited states in $^{134}$Sn, $^{133}$Sn and $^{132}$Sn was obtained from both $\beta$ and $\beta$n decay branches of indium isotopes.
$[1]$ V. Vaquero et al., Phys. Rev. Lett. 118, 202502 (2017).
$[2]$ I. Dillmann et al., Eur. Phys. J. A 13, 281 (2002).
$[3]$ M. Piersa et al., Phys. Rev. C 99, 024304 (2019).
$[4]$ P. Hoff et al., Phys. Rev. Lett. 77, 1020 (1996).
$[5]$ P. Hoff et al., Hyperfine Interact. 129, 141 (2000).
