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 $^{235}{\rm{Np}}$ and $^{237}{\rm{Np}}$. 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 $^{235}{\rm{Np}}$. 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 $^{235,\, 237}{\rm{Np}}$ is investigated. Finally, the possible reason for the signature splitting of the rotational band $\pi 5/2^-[523]$ in $^{237}{\rm{Np}}$ is explored, which may due to the different higher-order deformation $\varepsilon_6$ in these two signature branches of this band after upbending.