Spectroscopy of [sub 199,201]At

The excited states of 199At and 201At were studied using fusion evaporation reactions, a gas-filled recoil separator and various tagging methods. The level scheme of 201At was extended a lot including a cascade of magnetic dipole transitions, that is suggested to form a shears band. In addition, a 29/2+ [T1/2 = 3.39(9) s] isomeric state was observed. The 29/2+ state is suggested to originate from the p(h9/2) j200Po; 11􀀀i configuration, and it depopulates through 269-keV E2 and 339-keV E3 transitions. In both nuclei 199,201At we have observed also the isomeric 1/2+ [T1/2 = 273(9), 45(3) ms, respectively] intruder state, that is suggested to originate from the p(s1/2)􀀀1 configuration. The 1/2+ state decays through 103- keV and 269-keV E3 transitions in 199,201At, respectively. In both nuclei the 1/2+ state is fed from 3/2+ and 5/2+ states, which are suggested to originate from the p(d3/2)􀀀1 and p(d5/2)􀀀1 configurations, respectively.