Lifetimes and transition probabilities for the low-lying states in I131 and Xe132

Abstract

Lifetimes are measured for the low-lying states of $^{131}\mathrm{I}$ and $^{132}\mathrm{Xe}$ nuclei populated from the decay of radio-chemically separated Te fission fragments. The VENTURE array comprised of eight fast ${\mathrm{CeBr}}_{3}$ detectors is used for the lifetime measurement with $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ fast timing technique. Large basis shell model calculations have been performed with the ``nushellx'' code to interpret the low-lying level structure and to calculate level lifetimes in $^{131}\mathrm{I}$ and $^{132}\mathrm{Xe}$. The measured lifetimes and absolute transition probabilities are discussed in the light of systematics with the neighboring nuclei. Single particle excitation and loss of collectivity is observed with increasing neutron number up to $N=82$, validating the double shell closure at $^{132}\mathrm{Sn}$. Enhanced $B(E1)$ and $B(E3)$ strengths are found for the 1646-keV, 11/${2}^{\ensuremath{-}}$ level in $^{131}\mathrm{I}$.