Generalized seniority states and isomers in tin isotopes

Isomeric studies in neutron-rich nuclei are a powerful tool for exploring structure at the nuclear extremes. In this paper we discuss the systematic features of the excitation energies and transition probabilities of Sn isotopes in the region N. = 50-82 and present their basic understanding in terms of generalized seniority. We further use generalized seniority as a probe to explore the neutron-rich 6(+) seniority isomers in Sn134-138, and to validate the neutron single-particle energies beyond N = 82. We show that these isomers behave as generalized seniority isomers, where the so-called anomalous B(E2) behavior of the 6+ isomer in Sn-136 may be naturally explained. We support these results by shell model calculations, where the latest neutron single-particle energies of the N = 82-126 region have been used, and the i(13/2) neutron single-particle energy has been suitably modified in the renormalized charge-dependent Bonn interaction. This entails a possible new subshell closure at N = 112 due to the suggested higher location of the i(13/2) neutron orbital, also consistent with the choice of orbitals in the generalized seniority scheme. However, a small reduction in the f(7/2) two-body matrix elements is still required in the shell model calculations to consistently reproduce the experimental level energies as well as the transition probabilities in Sn134-138 isotopes.