The alternating-parity bands of \element{236,238}{U} and \element{238,240}{Pu} in a particle-number conserving method based on cranked shell model

TL;DR

This paper develops a particle-number conserving cranked shell model to study alternating-parity bands in uranium and plutonium isotopes, successfully reproducing experimental moments of inertia and revealing the role of octupole correlations in their rotational behaviors.

Contribution

The study introduces a PNC-CSM approach for reflection-asymmetric nuclei, providing new insights into octupole correlations and their impact on nuclear rotational properties.

Findings

Reproduces experimental moments of inertia and angular momentum alignments.

Links differences in U and Pu isotopes to octupole correlation strength.

Identifies nucleon pair alignments responsible for band upbendings.

Abstract

The particle-number conserving (PNC) method in the framework of cranked shell model (CSM) is developed to deal with the reflection-asymmetric nuclear system by applying the $S_x$ symmetry. Based on an octupole-deformed Nilsson potential, the alternating-parity bands in \element{236,238}{U} and \element{238,240}{Pu} are investigated. The experimental kinematic moments of inertia (MoI) and the angular momentum alignments of all studied bands are reproduced well in the PNC-CSM calculations. The striking difference of rotational behaviors between U and Pu isotopes can be linked to the strength of octupole correlations. The upbendings of the alternating-parity bands in\element{236,238}{U} are due to the alignments of pairs of nucleons occupying $\nu g_{9/2}$, $\pi f_{7/2}$ orbitals and $\nu j_{15/2}$, $\pi i_{13/2}$ high-$j$ intruder orbitals. Particularly, the interference terms of nucleon occupying the octupole-correlation pairs of $\nu^2 j_{15/2} g_{9/2}$ and of $\pi^2 i_{13/2} f_{7/2}$ give a very important contribution to the suddenly gained alignments.