Octupole correlations in odd-A lanthanides

Odd-A nuclei provide an informative test of the ability of octupole correlations to produce static or dynamic reflection-asymmetric nuclear deformations. Octupole effects in the lanthanide region are expected to be largest near N = 88, Z = 56-60, and an extensive set of data is now available on near yrast states in odd-Z Pm and Eu nuclei, and odd-N Sm nuclei. The odd-N Sm nuclei show complex yrast band structures, and although relatively strong electric dipole transitions have been observed there are no striking features characteristic of stable octupole deformation. 151Pm and 153Eu show yrast level schemes which are almost identical, consisting of two nearly degenerate K = 5/2 bands of opposite parity connected by strong and (within each nucleus) roughly constant strength electric dipole transitions. The situation is remarkably similar to that in the well known example of 223Th, with structures apparently appropriate to the motion of an odd nucleon in a reflection asymmetric potential. However, the magnetic properties of the two bands in 151Pm and 153Eu agree with a description in terms of separate orbits in a reflection-symmetric potential. This interpretation is supported by the agreement of the observed alignments with cranked shell model predictions