Level density of hot nuclei with A≤40

The light charged particles emitted from hot 40Ca compound nuclei, populated at excitation energy Ex=94 MeV and 〈J〉=20.5ħ by the reaction 130 MeV 16O on 24Mg, have been studied. Energy spectra of protons and alpha particles, measured in coincidence with evaporation residues and with a selection of multiple-alpha chains, have been compared with the predictions of Monte Carlo statistical model calculations. The comparison shows that the level density of hot nuclei with A≤40, needed to account for the measured quantities, is well predicted by the Fermi-gas model using a level-density parameter aeff=A/8 MeV-1 up to excitation energy 〈Eth/A〉∼1.7 MeV. In agreement with theory, light hot nuclei do not show the transition from aeff=A/8 MeV-1 to aeff∼A/13 MeV-1 evidenced in the A∼160 mass region for the same range of excitation energies Eth/A. The analysis of the alpha-particle spectra shows that the effects associated with the angular-momentum-induced deformations depend on the entrance channel characteristics and, in this case, are very small compared with those evidenced in the past for compound nuclei in the region A=50–70.