Dissipation of Energy and Angular Momentum by Emission of Neutrons and Gamma Rays

Abstract

We examine quantitatively some of the consequences of the statistical theory of nuclear de-excitation for neutron and $\gamma$-ray emission from highly excited nuclei. Special attention is given to the dissipation of angular momentum. To a first approximation, the nuclear "thermal energy" is removed first, initially by neutron and then by dipole $\gamma$-ray emission. The "rotational energy" is dissipated afterwards as a cascade of lowenergy $\gamma$ rays which may be composed of a high proportion of quadrupole radiation. The meager experimental data available are consistent with the theoretical expectations, but do not as yet permit a crucial test. Further possible experiments are pointed out. The role of the lowest-energy excited state at every angular momentum (yrast levels) is taken into account explicitly. The importance of using correct level densities at energies near the yrast levels, where the conventional level-density formulas may be very inaccurate, is stressed.