Level densities and γ-strength functions in 148,149Sm

The level densities and γ-strength functions of the weakly deformed ¹⁴⁸Sm and ¹⁴⁹Sm nuclei have been extracted. The temperature versus excitation energy curve, derived within the framework of the microcanonical ensemble, shows structures, which we associate with the breakup of Cooper pairs. The nuclear heat capacity is deduced within the framework of both the microcanonical and canonical ensembles. We observe negative heat capacity in the microcanonical ensemble whereas the canonical heat capacity exhibits an S shape as a function of temperature, both signals of a phase transition. The structures in the γ-strength functions are discussed in terms of the pygmy resonance and the scissors mode built on excited states. The samarium results are compared with data for the well-deformed ^161,162Dy, ^166,167Er, and ^171,172Yb isotopes and with data from (n,γ) experiments and giant dipole resonance studies.