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

Abstract
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 h 9/2 2 i 13/2 proton configuration. It decays to the states (h 9/2 2 f 7/2)23/2, (h 9/2 3)21/2, (h 9/2 3)17/2, (h 9/2 3)13/2 and (h 9/2 3)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 (h 9/2 2 i 13/2)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 e 2 fm6 can be reproduced by taking the value 0.9 MeV for the particle-phonon coupling matrix element ⟨i 13/2, 3-; 7/2|H coupl|f 7/2⟩.

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