136Ba studied via deep-inelastic collisions: Identification of the (νh11/2)10+-2 isomer

Abstract

A multinucleon transfer reaction between a thin self-supporting 78198Pt target and an 850 MeV 54136X6 beam has been used to populate and study the structure of the N=80 isotone 56136Ba. Making use of time-correlated γ-ray spectroscopy, evidence for an Iπ=(10+) isomeric state has been found with a measured half-life of 91±2 ns. Prompt-delayed correlations have also enabled the tentative measurement of the near-yrast states which lie above the isomer. Shell-model calculations suggest that the isomer has a structure which can be assigned predominantly as (vh 11/2)10+-2. The results are discussed in terms of standard and pair-truncated shell-model calculations, and compared to the even-Z N=80 isotones ranging from 50130Sn to 68148Er. A qualitative explanation of the observed dramatic decrease in the B(E2:10+→8+) value for the N=80 isotones at 136Ba is given in terms of the increasing single-hole energy of the h11/2 neutron configuration as the proton subshell is filled. The angular momentum transfer to the binary fragments in the reaction has also been investigated in terms of the average total γ-ray fold versus the scattering angle of the recoils