$\beta$-decay studies of $^{135-137}$Sn using selective resonance laser ionization techniques

The decays of the very neutron rich Sn isotopes $^{135-137}$Sn were studied at CERN/ISOLDE using isotopic and isobaric selectivity achieved by the use of a resonance ionization laser ion source and mass spectroscopy, respectively. Neutron decay rates, $\gamma$-ray singles, and $\gamma\gamma$-coincidence data were collected as a function of time. The half-life ( T$\scriptstyle_{1/2}$ ) and delayed neutron emission probability ( $p_{n}$ ) values of $^{135}$Sn were measured to be 530(20) ms and 21(3)%, respectively. For $^{136}$Sn, a T$\scriptstyle_{1 /2}$ of 250(30) ms was determined along with a $p_{n}\,$ value of 30(5) %. For $\,^{137}$Sn, a T$\scriptstyle_{1/2}$ of 190(60) ms and a $p_{n}$ value of 58(15)% were deduced. Identification of low-energy transitions in $^{135}$Sb was made possible by comparison of laser-on and laser-off $\gamma$-ray spectra. Those data combined with $\gamma\gamma$-coincidence spectra were used to construct a level scheme for $^{135}$Sb that includes an unexpectedly low first excited state at 282 keV. A ground state $\beta$-branch of 33.2% was measured by following the growth and decay of the $^{135}$Sb daughter. Shell-model calculations are consistent with the observed $^{135}$Sb level structure and can account for a lowered first excited state.