Introduction

At the end of the pre-equilibrium stage, or a thermalizing process, the residual nucleus is supposed to be left in an equilibrium state, in which the excitation energy \(E^*\) is shared by a large number of nucleons. Such an equilibrated compound nucleus is characterized by its mass, charge and excitation energy with no further memory of the steps which led to its formation. If the excitation energy is higher than the separation energy, it can still eject nucleons and fragments (d, t, ³He, \(\alpha\), others). These constitute the low energy and most abundant part of the emitted particles in the rest system of the residual nucleus. The emission of particles by an excited compound nucleus has been successfully described by comparing the nucleus with the evaporation of molecules from a fluid [Fre36]. The first statistical theory of compound nuclear decay is due to Weisskopf and Ewing [WE40].

Bibliography

Fre36

J Frenkel. On the absorption of light and the trapping of electrons and positive holes in crystalline dielectrics. Phys. Zs. Sowjetunion, 9:533–536, 1936.

WE40

V. F. Weisskopf and D. H. Ewing. On the yield of nuclear reactions with heavy elements. Physical Review, 57(6):472–485, mar 1940. URL: https://doi.org/10.1103/PhysRev.57.472, doi:10.1103/physrev.57.472.