Nuclear level density at low excitation energies is proposed as an indicator of the first order phase transitions in nuclei. The new signature, a maximum value of the level density at the critical point, appears to be sensitive to the detailed way the phase transition takes place in different nuclear regions: it is consistent with phase coexistence in the $N=90$ region, and with a rapid crossing of the two phases, without their coexistence/mixing at the critical point in the $N=60$ region, respectively. Candidates for critical point nuclei are proposed for odd-mass and odd-odd nuclei, using correlations between relative excitation energies, and their ratios, for structures (bands) based on unique-parity orbitals.

• Received 6 June 2018

DOI:https://doi.org/10.1103/PhysRevC.98.024301