Intermediate-state decay rates in the exciton model

Abstract

Listen

Translate article

New calculations of the decay rates (for particle emission and exciton-exciton interactions) of the intermediate states of the composite nucleus,during equilibration, are reported. In these calculations, densities of p-particle, h-hole states corresponding to non-equidistant single-nucleon state spacings have been used. The decay rates for particle emission have been estimated with the detailed balance principle, while a semiphenomenologieal approach is proposed to evaluate the decay rates for exciton-exciton interactions. In principle, these decay rates can be evaluated starting from the probabilities per unit time of particle-particle and hole-hole collisions inside the nucleus. Inspection of experimental data, however, indicates that although the energy and exciton number dependence of the decay rates appear to be reasonable, the absolute value is too high. The required reduction is obtained by normalising the theoretical value of the decay rate of a 2p-1h excited system to the experimental one deduced from the study of (p, n) reactions. This procedure is somewhat tentative, the underlying difficulty being the lack of basic knowledge of the nucleon-nucleon scattering cross section in nuclear matter. However, the use of the deduced decay rates appears to allow consistent reproduction of absolute cross sections for proton induced reactions in nuclei of widely differing mass, in the incident energy interval ≈ 15 to ≈ 50 MeV.