${\hat{I}}^2$-Decay Half-Lives of 55 Neutron-Rich Isotopes beyond the N=82 Shell Gap

Abstract

The ${\hat{I}}^2$-decay half-lives of 55 neutron-rich nuclei ${}^{134-139}$Sn, ${}^{134-142}$Sb, ${}^{137-144}$Te, ${}^{140-146}$I, ${}^{142-148}$Xe, ${}^{145-151}$Cs, ${}^{148-153}$Ba, ${}^{151-155}$La were measured at the Radioactive Isotope Beam Factory (RIBF) employing the projectile fission fragments of ${}^{238}$U. The nuclear level structure, which relates to deformation, has a large effect on the half-lives. The impact of newly-measured half-lives on modeling the astrophysical origin of the heavy elements is studied in the context of $r$ process nucleosynthesis. For a wide variety of astrophysical conditions, including those in which fission recycling occurs, the half-lives have an important local impact on the second ($A$ $\approx$ 130) peak.