Research On Reflection Asymmetric Nuclei Using A Particle Number Conserving Method Based On Cranked Shell Model

The octupole collective modes has long been a significant topic in nuclear structure physics. Previously, a cranked shell model(CSM) with the pairing correlations treated by a particle number conserving(PNC) method has achieved great success in studies of nuclear structure with reflection symmetric deformed potential, while the properties of reflection asymmetric deformed nuclei cannot be described. In this work, the CSM-PNC method is improved and used in the reflection asymmetric deformed nuclei, for the first time.In this work, the octupole deformation freedom is introduced in the Nilsson potential. The octupole deformed CSM Hamiltonian with momopole and quadrupole pairing correlations is treated by using of PNC method, and the low-lying excited intrinsic reflection asymmetric rotational bands(RABs) are solved exactly. The octupole collective stability is discussed, and a description for the positive and negative parity bands is given in the limit of stable octupole deformed mode in high spin states.In the CSM-PNC frame work, the essential experimental indicators, namely, the alternating parity bands in even-even nuclei and the parity doublets in odd-A nuclei are evaluated taking 236,237,238 U and 238,239,240 Pu as examples. The kinematic moments of inertia(MOIs) and angular momentum alignments of rotational bands, and Simplex splitting in odd-A nuclei bands are reproduced quite well. The striking difference of rotational properties between U isotopes and Pu isotopes are analyzed by the cranking frequency dependence of the occupation probability of each cranked Nilsson orbital near the Fermi surface and the contributions of valence orbitals from high-j orbitals to the angular momentum alignment, and the upbendings mechanics are shown clearly. The paring gap of RABs and reflection symmetric deformed bands are given by the CSM-PNC calculations. The influence of octupole deformed field on paring gap is discussed, and the pairing gap is sensitive to the octupole deformation.A prospection of the studies of reflection asymmetric deformed nuclei within the CSM-PNC frame work is given, for instance, parity projection method and axial octupole effects.