Thermal population of nuclear excited states

The bound state populations of ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ fragments emitted from ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$ compound nuclei formed in the reaction of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ have been measured. At bombarding energies in the range of 87.5–112 MeV, these populations are consistent with emission from the thermally equilibrated compound nucleus when the rotational energy of the compound system is taken into account. The results demonstrate for the first time that nuclear excited state populations reflect the temperature of compound nuclei which reach statistical equilibrium. At higher bombarding energies the population distributions remain constant which signals the onset of non-compound nucleus reactions.