Existence of Intrinsic Octupole Shape in Pm151 : the Reflection Asymmetric Triaxial Particle Rotor Model

The possibility of the existence of octupole deformation in 151Pm has caused interest for about thirty years. In this paper, the observed low-lying positive- and negative-parity structures in 151Pm are investigated by the reflection-asymmetric triaxial particle rotor model. The experimental energy spectra, energy staggering, and parity splitting parameters are well reproduced by the theoretical calculations. It is found that, although the energy spectra can be reproduced without the octupole degree of freedom, the calculated B(E 1) values depend sensitively on the octupole deformation parameter /30, and the observed enhanced E1 transitions can be reproduced with a notable /30 = 0.07. The detailed analysis of the intrinsic wave functions shows that these nearly degenerate positive- and negative-parity bands are built on two individual proton configurations, i.e., dominated by ng7/2[Q = 5/2] and nh11/2[Q = 5/2], respectively, which differs from the parity doublet bands built on a single parity-mixed configuration.