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 γ -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) ⊗ πg7/2 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.
Instytucja finansująca badania:Italian Istituto Nazionale di Fisica Nucleare, the Polish National Science Centre, Poland, under research project No. 2020/39/D/ST2/03510, the Polish National Agency for Academic Exchange (NAWA) within the Bekker programme under Grant PPN/BEK/2020/1/00431/U/00001, the Institute for Basic Science (IBS-R031-D1), the German DFG
under grant JO391/18-1, and the Fonds de la Recherche Scientifique - FNRS under Grants No. J.0174.22 and No. 4.45.10.08.