De-Excitation of Highly Excited Nuclei

We describe a scheme of calculations useful for computer evaluation of the de-excitation of nuclei having large excitation energies and angular momenta. The scheme is based on the statistical model. Cascade emission of $\gamma$ rays is taken into account. In particular, we include consideration of both dipole and quadrupole $\gamma$-ray emission, and of the crucial role played by the lowest excited state at every angular momentum in the nuclei involved. We are thus, for example, in a position to study phenomena connected with particle emission following $\gamma$-ray emission. As input in a sample calculation (${\mathrm{Ce}}^{140}$+$0^{16}$ at 90 MeV, lab) we use information obtained from experimental data and from the optical and shell models, but independent of the data with which comparisons are made. We find generally reasonable agreement, and no serious disagreements, with a variety of experimental data, with no parameter adjustment. The predicted energy spectra of emitted $\alpha$ particles and $\gamma$ rays show important features not demonstrated in previous, less complete calculations. The $\gamma$ spectrum displays a low average energy of less than 1.0 MeV. The number of photons emitted by quadrupole radiation is typically of the same order of magnitude as the number emitted by dipole radiation. Other results are also described.