Lifetimes in At211 and their implications for the nuclear structure above Pb208

Lifetimes of excited states in At-211 were measured using the electronic gamma-gamma fast timing technique. The nucleus of interest was populated in a Pb-208(Li-6, 3n)(211) At fusion-evaporation reaction at the FN Tandem accelerator of the Institute for Nuclear Physics, University of Cologne. The lifetimes of the 17/2(1)(-) and 23/2(1)(-) states were determined, together with an upper limit for the 13/2(1)(-) state. The experimental results are compared to two shell-model calculations, one using a semiempirical interaction for three particles in a single j = 9/2 shell and the other using the modified Kuo-Herling interaction in a multi- j model space.