Thermal Quenching of Pair Correlations in Rare Earth Nuclei

The γ-ray spectra of the (³He,αγ) pick-up reaction on ^162,163Dy and ^172,173Yb are utilized to extract level densities. The temperature T as function of excitation energy E is deduced within the microcanonical ensemble. Oscillations in T(E) are interpreted as the breaking of Cooper pairs. The deduced heat capacity in the canonical ensemble shows an S-form indicating a critical temperature for quenching of pair correlations at T_c = 0.50(4) MeV.