β-decay studies of135–137Snusing selective resonance laser ionization techniques

Abstract

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