An outstanding puzzle in the structure of very heavy nuclei lies in the rotation response of deformed transuranic isotopes. While the rotation alignment of pairs of $i_{13/2}$ protons is ubiquitous and well understood, observing the analogous alignment of the $j_{15/2}$ neutrons has been elusive. In this work we present a new quantitative analysis approach: from their moments of inertia as a function of frequency, we compare the alignments of rotational bands with both “low” and high-$j$ intrinsic structures in the $N=151$ isotones of Pu, Cm, Cf, and No, thereby distinguishing between the alignments of neutron versus proton pairs through “blocking” effects. In this way, the alignment of $j_{15/2}$ neutrons can be clearly identified for the first time. The protons and neutrons begin aligning at a very similar frequency. The contribution of $j_{15/2}$ neutrons to the total alignment is found to grow with increasing $Z$ compared to $i_{13/2}$ protons. To explain these observations, it is necessary to adopt a self-consistent set of single-particle energies corresponding to the nuclear shape that minimizes the mass. The shape description needs to include high-order deformations up to at least ${\beta }_6$.

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• Collective levels
• High spin states
• Nuclear structure & decays
• A ≥ 220