Double-Magic Nature of 132Sn and 208Pb through Lifetime and Cross-Section Measurements

Single-neutron states in Sn-133 and Pb-209, which are analogous to single-electron states outside of closed atomic shells in alkali metals, were populated by the (Be-9, Be-8) one-neutron transfer reaction in inverse kinematics using particle-gamma coincidence spectroscopy. In addition, the s(1/2) single-neutron hole-state candidate in Sn-131 was populated by (Be-9, Be-10). Doubly closed-shell Sn-132 (radioactive) and Pb-208 (stable) beams were used at sub-Coulomb barrier energies of 3 MeV per nucleon. Level energies,gamma-ray transitions, absolute cross sections, spectroscopic factors, asymptotic normalization coefficients, and excited-state lifetimes are reported and compared with shell-model expectations. The results include a new transition and precise level energy for the 3p(1/2) candidate in Sn-133, new absolute cross sections for the 1h(9/2) candidate in Sn-133 and 3s(1/2) candidate in Sn-131, and new lifetimes for excited states in Sn-133 and Pb-209. This is the first report on excited-state lifetimes of Sn-133, which allow for a unique test of the nuclear shell model and Sn-132 double-shell closure.