Electric-dipole transition probabilities between yrast bands in 157Gd

Abstract

High-spin states of the stable 157Gd nucleus were studied by a γ–γ coincidence measurement using multiple Coulomb excitation with a 136Xe beam. Two rotational bands of the opposite parity coexisting along the yrast line were extended up to 29/2− and 29/2+, respectively, one of which was of a νh9/2 configuration and the other was of a νi13/2 configuration. Fifteen E1 transitions from the νh9/2 band to the νi13/2 band were observed. Absolute reduced transition probabilities, B(E1), of these transitions were derived from the branching ratios obtained in this experiment and the lifetimes measured in our previous experiment. The B(E1) values ranged between 0.36×10−4 and 5.2×10−4 [e2fm2]. This enhancement could be explained by introducing a parameter which effectively takes into account the octupole softness. It was also found that the matrix elements of the E1 transitions had a term proportional to If(If+1)−Ii(Ii+1) understood in terms of Coriolis mixing.