Evidence for an Isomeric 29/2+ Level in 211At

A 70 ns isomeric state at 2 641 keV has been produced in the 209Bi(α,2n)211 At reaction and interpreted as the 29/2+ state of the h9/22 i13/2 proton configuration. It decays to the states (h9/22 f7/2)23/2, (h9/23)21/2, (h9/23)17/2, (h9/23)13/2 and (h9/23)9/2 by a straight cascade of transitions with energies (multipolarities) 713.3 keV (E3), 511.6 keV (M1), 96.0 keV (E2), 253.4 keV (E2), and 1 066.9 keV (E2). There is also indirect evidence for a 24.4 keV (E2) branch to a (h9/22 i13/2)25/2 state followed by a 688.9 keV (E1) transition to the 21/2- state. The reduced transition rate B(E3, 29/2+ → 23/2-) = 51 000 e2 fm6 can be reproduced by taking the value 0.9 MeV for the particle-phonon coupling matrix element i13/2, 3-; 7/2|Hcoupl|f7/2.