Nuclear shape transitions at finite temperature

Changes in shape in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ are studied at T≠0 both in finite-temperature mean-field calculations and in the exact canonical ensemble. With increasing temperature the canonical ensemble average of the rotational energy spectrum tends toward a more equispaced harmonic spectrum. This deformed to spherical transition gives rise to a peak in the specific heat which is also seen in finite-temperature Hartree-Fock approximation albeit at a slightly higher temperature. The canonical ensemble average of the quadrupole moment does not, however, appear to vanish at the critical temperature as is the case in the finite-temperature Hartree-Fock approximation.