Unpaired band crossings

The lack of systematic band crossings at high spin in ${}_{}{}^{159}{}_{}{}^{}$,160Er and the selectivity of the single observed neutron band crossing at ħω>0.37 MeV in ${}_{}{}^{159}{}_{}{}^{}\mathrm{Er}$ (i) indicate that static neutron-pair correlations are too weak for the excitation of a pair of quasineutrons, and (ii) can be explained in terms of the expected spectrum of single-neutron states in the absence of static pair correlations.