Fast Electric Dipole Transitions in Ra-Ac Nuclei

Abstract

Lifetimes of levels in 225Ra, 225Ac, and 227Ac have been measured by delayed coincidence techniques and these have been used to determine the E1 gamma-ray transition probabilities. The reduced E1 transition probabilities in 225Ra and 225Ac are about two orders of magnitude larger than the values in mid-actinide nuclei. On the other hand, the E1 rate in 227Ac is similar to those measured in heavier actinides. Previous studies suggest the presence of octupole deformation in all the three nuclei. The present investigation indicates that fast E1 transitions occur for nuclei with octupole deformation. However, the studies also show that there is no one-to-one correspondence between E1 rate and octupole deformation. 1. Introduction Recent theoretical calculations [Cha80, Lea82, Lea84a] and measurements [Ahm82, She83, Ahm84] show that strong octupole correlation and/or octupole deformation effects play an important role in the description of nuclides in the mass 220-230 region. A signature of octupole