Systematic investigation of the high-$K$ isomers and the high-spin rotational bands in the neutron rich Nd and Sm isotopes by a particle-number conserving method

Abstract

The rotational properties of the neutron rich Nd and Sm isotopes with mass number $A\approx150$ are systematically investigated using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the Pauli blocking effects are taken into account exactly. The 2-quasiparticle states in even-even Nd and Sm isotopes with excitation energies lower than 2.5~MeV are systematically calculated. The available data can be well reproduced and some possible 2 and 4-quasiparticle isomers are also suggested for future experiments. The experimentally observed rotational frequency variations of moments of inertia for the even-even and odd-$A$ nuclei are reproduced very well by the calculations. The effects of high-order deformation $\varepsilon_6$ on the 2-quasiparticle excitation energies and moments of inertia of the ground state bands in even-even Nd and Sm isotopes are analyzed in detail. By analyzing the occupation probability $n_\mu$ of each cranked Nilsson orbitals near the Fermi surface and the contribution of each major shell to the angular momentum alignments, the alignment mechanism in these nuclei is understood clearly.