Risk of Misinterpretation of Nearly Degenerate Pair Bands as Chiral Partners in Nuclei

The experimental information on the observed nearly degenerate bands in the N=75 isotones, in particular ¹³⁴Pr⁡ and ¹³⁶Pm, which are often considered as the best candidates for chiral bands, is critically analyzed. Most properties of the bands, in particular, the recently measured branching ratios and lifetimes, are in clear disagreement with the interpretation of the two bands as chiral bands. For I=14–18 in ¹³⁴Pr⁡, where the observed energies are almost degenerate, we have obtained a value of 2.0(4) for the ratio of the transition quadrupole moments of the two bands, which implies a considerable difference in the nuclear shape associated with the two bands. The insufficiency of the near-degeneracy criterion to trace nuclear chirality is emphasized.