Experimental study of 1/2(+) isomers in At-199,At-201

Abstract

Using fusion-evaporation reactions, a gas-filled recoil separator, and recoil-electron and recoil-electron-α tagging techniques, a new isomeric 1 2 + state [T1/2 = 45(3) ms] in 201At is identified, and an earlier reported corresponding state [T1/2 = 273(9) ms] in 199At is confirmed. The 1 2 + state is suggested to originate from an intruder π(s1/2) −1 configuration. In addition, nuclear structure of states below and above this 1 2 + state are studied in both nuclei. The isomer decays through a cascade of an E3 transition followed by a mixed M1/E2 transition to the 9 2 − ground state, and it is interpreted to be fed from nearly spherical 3 2 + and 5 2 + states originating from π(d3/2) −1 and π(d5/2) −1 configurations, respectively.