Prompt fission gamma rays

Abstract

The spectrum of prompt γ-rays emitted by the fission fragments in the thermal neutron-induced fission of ²³⁵U has been exactly calculated within the framework of the basic statistical theory assumptions for the emission of neutrons and γ-quanta from excited nuclei. The shape of the spectrum corresponds approximately with the shape obtained experimentally but the computed total energy carried away by the γ-quanta (⪅6·2 MeV) is appreciably less than the experimentally determined amount (8–9 MeV). It is possible to remove this discrepancy if, in calculating the residual excitations, one takes into account the ‘thinning out’ of the levels of the fission fragment nuclei in the vicinity of the ground state.