  Particle-gamma coincidences have been measured to obtain gamma-ray spectra as
a function of excitation energy for 231-233Th and 237-239U. The level
densities, which were extracted using the Oslo method, show a constant
temperature behavior. The isotopes display very similar temperatures in the
quasi-continuum, however, the even-odd isotopes reveal a constant entropy
increase Delta S compared to their even-even neighbors. The entropy excess
depends on available orbitals for the last unpaired valence neutron of the
heated nuclear system. Also, experimental microcanonical temperature and heat
capacity have been extracted. Several poles in the heat capacity curve support
the idea that an almost continuous melting of Cooper pairs is responsible for
the constant-temperature behavior.
