Thermodynamic properties ofFe56,57

Abstract

Nuclear level densities for $^{56,57}\mathrm{Fe}$ have been extracted from the primary $\ensuremath{\gamma}$-ray spectra using (${}^{3}\mathrm{He}, {}^{3}{\mathrm{He}}^{'}\ensuremath{\gamma}$) and (${}^{3}\mathrm{He}, \ensuremath{\alpha}\ensuremath{\gamma}$) reactions. Nuclear thermodynamic properties for $^{56}\mathrm{Fe}$ and $^{57}\mathrm{Fe}$ are investigated using the experimental level densities. These properties include entropy, Helmholtz free energy, caloric curves, chemical potential, and heat capacity. In particular, the breaking of Cooper pairs and single-quasiparticle entropy are discussed and shown to be important concepts for describing nuclear level density. Microscopic model calculations are performed for level densities of $^{56,57}\mathrm{Fe}$. The experimental and calculated level densities are compared. The average number of broken Cooper pairs and the parity distribution are extracted as a function of excitation energy for $^{56,57}\mathrm{Fe}$ from the model calculations.