Enhanced and quenched B(E1) transition rates between parity doublet bands in 227Ra

Abstract

The fast timing βγγ( t) method has been used to measure level lifetimes in the parity doublet bands in 227Ra populated in the β − decay of 227Fr. In particular T 1 2 = 254(9) ps, 236(30) ps, ⩽41 ps and 16(13) ps have been measured for the 3 2 − and 5 2 − members of the K π = 3 2 − band and for the 1 2 − and 3 2 − members of the K π = 1 2 − band, respectively. These results indicate surprisingly fast B(E1) rates in this octupole transitional nucleus with the average | D 0 | value of ⩾ 0.11 e·fm for the K π = 1 2 − band and | D 0 |= 0.10 e·fm for K π = 3 2 − band. The general enhancement (and occasional quenching) of E1 intra-doublet and some enhanced extra-doublet transitions in 227Ra are interpreted within the quasiparticle-plus-phonon model with the inclusion of Coriolis coupling. Similar calculations, performed for 223Ra, are found to be in good agreement with the experimental data.