Observation ofK=1/2octupole deformed bands in227Th

Abstract

High-spin states in 227Th have been populated using the reaction 226Ra(α,3n)227Th at a bombarding energy of 33 MeV. The high-spin rotational structures of this nucleus have been refined and extended. In addition, the linking of these structures with the low-spin states known from 231U α decay has allowed a comprehensive decay scheme of this nucleus to be assembled for the first time. Four previously known rotational bands are interpreted as Coriolis coupled Kπ=1/2+ and Kπ=1/2− bands, in agreement with predictions using a reflection-asymmetric mean field approach. The determination of decoupling parameters for these bands is consistent with the a(Kπ=1/2+)=−a(Kπ=1/2−) rigid octupole rotor expectation. A further rotational band is interpreted as having Kπ=3/2−. Measured D0/Q0 ratios are consistent with an interpolation of the values given for neighboring even-even nuclei, providing further evidence for the significance of strong octupole correlations in this nucleus.