A gamma-ray cascade model for the calculation of average ?-ray multiplicities and isomeric cross section ratios

Abstract

The calculations of theγ-ray cascades following the decay of a compound state were carried out using all levels with known values of energy, spin and parity at low energy and statistical assumptions for the distribution of the nuclear levels in the energy range between the initially occupied compound state and the low-lying levels. Dipole and quadrupole transitions were taken into account. The model works without the introduction of an artificial average transition energy. The model was applied to the calculation of averageγ-ray multiplicities and of isomeric cross section ratios. The applications to the determination of level density parameters are discussed. It was shown that it is not allowed to neglect the contribution of quadrupole radiation in the cascade as was done in other models in the past. Only in the case of In115(n, γ) In116 enough data are available to determine statistical parameters. We get for the level density parametera=18.6 MeV−1, for the spin cut-off factorσ=4.8 and a contribution of about 5% quadrupole radiation in the cascade.