Study of the three-proton three-neutron-hole nucleus 208At

Levels in 208At were populated in the 209Bi(α, 5n) reaction, and the subsequent radiation was studied using γ-spectroscopic methods including γ-ray excitation function and angular distribution, γγ(t) coincidence and γt measurements, as well as measurements of conversion electrons. The excited spectrum of 208At is found to consist of two almost disconnected parts which are proposed to originate from seniority-three proton and neutron cascades. Two isometric states are observed. A T12 = 45 ± 2 ns state at 1090 keV is proposed to have the main configuration πh92j20+vi−1132j−20+ and Jπ = 10−. A high-spin isomer with T12 = 1.5 ± 0.2 μs at 2276 keV is assigned to be the π(h292i132)292+vf−152j−20+Jπ = 16− state. Shell-model arguments are used to assign configurations to most of the observed levels. Transition rates are discussed.