Astrophysical Implication of Low E(2_1~+) in Neutron-rich Sn Isotopes

摘要

The observation and prediction of unusually depressed first excited 2_1~+ states in even-A neutron - rich isotopes of semi-magic Sn above ~(132)Sn provide motivations for reviewing the problems related to the nuclear astrophysics in general. In the present work, the β-decay rates of the exotic even Sn isotopes~(134,136)Sn) above the ~(132)Sn core have been calculated as a function of temperature (T). In order to get the necessary ft values, B(GT) values corresponding to allowed Gamow Teller (GT—) β-decay have been theoretically calculated using shell model. The total decay rate shows decrease with increasing temperature as the ground state population is depleted and population of excited states with slower decay rates increases. The abundance at each Z value is inversely proportional to the decay constant of the waiting point nucleus for that particular Z. So the increase in half-life of isotopes of Sn, like ~(136)Sn, might have substantial impact on the r-process nucleosynthesis.