First $β$-decay spectroscopy of $^{135}$In and new $β$-decay branches of $^{134}$In

Abstract

The $β$ decay of the neutron-rich $^{134}$In and $^{135}$In was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number $Z=50$ above the $N=82$ shell. The $β$-delayed $γ$-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three $β$-decay branches of $^{134}$In were established, two of which were observed for the first time. Population of neutron-unbound states decaying via $γ$ rays was identified in the two daughter nuclei of $^{134}$In, $^{134}$Sn and $^{133}$Sn, at excitation energies exceeding the neutron separation energy by 1 MeV. The $β$-delayed one- and two-neutron emission branching ratios of $^{134}$In were determined and compared with theoretical calculations. The $β$-delayed one-neutron decay was observed to be dominant $β$-decay branch of $^{134}$In even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of $^{134}$Sn. Transitions following the $β$ decay of $^{135}$In are reported for the first time, including $γ$ rays tentatively attributed to $^{135}$Sn. In total, six new levels were identified in $^{134}$Sn on the basis of the $βγγ$ coincidences observed in the $^{134}$In and $^{135}$In $β$ decays. A transition that might be a candidate for deexciting the missing neutron single-particle $13/2^+$ state in $^{133}$Sn was observed in both $β$ decays and its assignment is discussed. Experimental level schemes of $^{134}$Sn and $^{135}$Sn are compared with shell-model predictions. Using the fast timing technique, half-lives of the $2^+$, $4^+$ and $6^+$ levels in $^{134}$Sn were determined.