The low-seniority shell-model structure of 212At

Abstract

Using the reaction 209Bi(α, n), states in the nucleus 212At were populated. The decay of excited states was studied using conventional in-beam γ-ray and conversion-electron spectroscopy. A great number of new levels were established and assigned spins and parities and the previously reported yrast cascade was confirmed. A new T 1 2 = 32 ± 1 ns isomer at 275.4 keV is reported and interpreted to be the 5 − state of the πj 0 + 2 h 9 2 ν g 9 2 configuration. The configurations were calculated as belonging to the neutron-proton seniority-2 multiplets where the available orbitals are h 9 2 , f 7 2 and i 3 2 for the protons and g 9 2 , i 11 2 and j 15 2 for the neutrons. Configuration mixing is shown to be essential in order to account for the experimental findings. On the basis of isomeric lifetimes the effective charges are discussed.