Transition probabilities near100Sn and the stability of theN,Z=50shell closure

Abstract

Recent $B(E2;{0}_{\mathrm{g}.\mathrm{s}.}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ measurements in light tin isotopes have revealed surprisingly large values relative to standard shell model predictions, generating an unexpected asymmetry in the $B(E2)$ values with respect to the neutron midshell. This effect has triggered various speculations as to its origin, such as a possible weakening of the $N,Z=50$ shell closure. Here we present new shell model calculations to investigate the origin of the observed asymmetric character of the $B(E2)$ values in the tin isotopes. By including the effects of the neutron ${g}_{9/2}$ orbital below the $N=50$ shell gap it is shown that Pauli blocking effects may play an important role near the $N=50$ shell closure. A new set of single-particle energies and monopole interactions, fitted to the experimental data in the region, together with the isospin-dependent effective charge suggested by Bohr and Mottelson is shown to reproduce the experimental transition rate values in the Sn isotopic chain.