The role $j_{15/2}$ neutron orbitals play in the transuranic region of actinides has been studied by exploring $\gamma$-ray transitions between yrast states in ${}^{235}\mathrm{Np}$, populated utilizing the nucleon-transfer reaction ${}^{237}\mathrm{Np}$(${}^{116}\mathrm{Sn}$,${}^{118}\mathrm{Sn}$). Two rotational sequences, presumably the two signatures of the ground-state band, have been delineated to high spin for the first time, with the $\alpha =+1/2$ and $\alpha =-1/2$ signature partners reaching $49/2^{+}\hslash$ (tentatively $53/2^{+}\hslash$) and $47/2^{+}\hslash$ (tentatively $51/2^{+}\hslash$), respectively. Definite isotopic assignments for these in-band transitions were established through $\gamma$-ray cross correlations between ${}^{235}\mathrm{Np}$ and ${}^{118}\mathrm{Sn}$ and events where at least three $\gamma$ rays corresponding to neptunium-like particles were detected. These transitions reveal clear upbends in the aligned angular momentum and kinematic moment of inertia plots; such a phenomenon could indicate a strong interaction between an aligned $\nu j_{15/2}$ configuration crossing the ground-state band in ${}^{235}\mathrm{Np}$, which is based on a $\pi i_{13/2}$ orbital. However, the lack of any signature splitting over the observed frequency range of the ${}^{235}\mathrm{Np}$ rotational sequences cannot remove the possibility of a $\pi h_{9/2}$ assignment for the observed band. The role of the $\nu j_{15/2}$ and $\pi i_{13/2}$ alignment mechanisms in the deformed U-Pu region is discussed in light of the current spectroscopic data and in the context of the cranked-shell model.

• Received 9 September 2009

DOI:https://doi.org/10.1103/PhysRevC.81.014312