Angular and energy distribution of fission neutrons

Abstract

The angular distribution of fission neutrons given by the statistical model of the nucleus is calculated, taking account of the angular anisotropy of emission of fission fragments. The latter is represented by the simple expression 1 + k cos²α. It is assumed that the neutrons are emitted isotropically in the co-ordinate system in which the appropriate fragment is at rest. The ratio P of fission neutron intensities emitted parallel and perpendicular to the primary neutron beam is calculated for ²³⁸U, the energy range 1–10 MeV being covered for both primary and secondary neutrons. When the fission is considered to be induced by neutrons of the fission spectrum, the mean value of P for ²³⁸U comes to ∼1·13. The energy spectrum of the fission neutrons is also calculated for various values of the incident neutron energy. Anisotropies occurring in the fission of other nuclei may be calculated by the same method.