Nuclear structure study for the neutron-rich nuclei beyond 132Sn: In-beam gamma-ray spectroscopy of 136Sn and 132Cd

The neutron-rich nuclei 136 Sn and 132 Cd have been studied in the purpose of nuclear structure for the nuclei beyond the doubly-magic nucleus 132 Sn. The 2 + 1 → 0 + gs transitions were identified for these two nuclei using in-beam γ -ray spectroscopy in coincidence with one- and two-proton removal reactions, respectively, at the RIKEN Radioactive Isotope Beam Factory. The 2 + 1 state in 136 Sn is found to be similar to that for 134 Sn indicating the seniority scheme may also hold for the heavy tin isotopes beyond N = 82. For 132 Cd, the 2 + 1 state provides the first spectroscopic information in the even-even nuclei locating in the region “southeast” of 132 Sn and the result is discussed in terms of proton-neutron configuration mixing. In both these two nuclei, it was found that the valence neutrons play an essential role in their low-lying excitations.