Testing the predictive power of realistic shell model calculations via lifetime measurement of the 11/2+state in 131Sb

Abstract

The lifetime of the 11/2+1 state in the 131Sb nucleus was measured at the LOHENGRIN spectrometer of the Institut Laue-Langevin via neutron-induced fission of 235U using gamma-ray fast-timing techniques. The obtained value of T1/2 = 3 (2) ps, at the edge of the sensitivity of the experimental method, is the first result for the 11/2+1 state half-life in neutron-rich Sb isotopes. The corresponding quadrupole reduced transition probability to the ground state is B(E2) = 1.4+1.5 -0.6W.u., indicating a noncollective nature of this state. Realistic shell-model calculations performed in a large valence space reproduce well the experimental value and point to a dominant 2+(130Sn) circle times pi g7/2 configuration for the 11/2+1 state, as expected in a weak-coupling scenario. At the same time, the sum of the quadrupole strength of the multiplet states is predicted to exceed the one of the 130Sn core as a consequence of the equal contribution of the proton and the proton-neutron quadrupole matrix elements, pointing to possible development of collectivity already in the close neighborhood of 132Sn.