Inelastic Neutron Scattering byU238

Abstract

Monoenergetic neutrons in the range 0.5 to 2 Mev have been scattered from ${\mathrm{U}}^{238}$ and the spectra of scattered neutrons have been investigated by a time-of-flight method. Levels have been located at 0.044±0.004, 0.146±0.006, 0.30±0.03, 0.73±0.02, 0.98±0.02, 1.06±0.03, and 1.26±0.04 Mev. The cross sections for excitation of these levels have been obtained corresponding to inelastic neutron scattering at 90°. An angular distribution has been obtained for the inelastically scattered neutrons corresponding to excitation of the 44-kev level by incident neutrons of 550-kev energy. This distribution is of the form $A(1-B{cos}^2\theta )$ where $A$ is 0.135±0.02 barn per steradian and $B$ is 0.45±0.1. The cross section is in good agreement with calculations by Chase and Wilets which indicate compound nucleus formation is the dominant mechanism in inelastic neutron scattering by ${\mathrm{U}}^{238}$ at 550 kev, although the anisotropy is larger than that predicted.