Theoretical Investigation of the High-spin States in ^{235, 237}Np

The rotational properties of the actinides are quite important for revealing the alignment mechanism, pairing correlations, level structure etc., of the nuclei in A \approx 250 mass region. On the one hand, investigation of the high-spin structures of these nuclei can provide benchmark for testing various theoretical models. On the other hand, it can help us to get more information about the superheavy nuclei. In this work, the particle-number conserving method based on the cranked shell model is adopted to investigate the rotational bands observed in ^235\rmNp and ^237\rmNp. The moments of inertia, alignments etc., are reproduced by the calculations. Firstly, the ab formula which is used to investigate the rotational spectra, is adopted to determine the bandhead spin of the rotational bands observed in ^235\rmNp. Secondly, by comparing the experimental and calculated moments of inertia, the configuration for this signature partner band is assigned as \pi 5/2^-523. Moreover, the influence of higher-order deformation \varepsilon_6 on the alignments of neutron j_15/2 is discussed. The appearance of the neutron j_15/2 alignment in the calculations, which is non-existent in experiment, is explored. The upbending mechanism in ^235,\, 237\rmNp is investigated. Finally, the possible reason for the signature splitting of the rotational band \pi 5/2^-523 in ^237\rmNp is explored, which may due to the different higher-order deformation \varepsilon_6 in these two signature branches of this band after upbending.