A Cloud-Chamber Study of the Scattering of Fast Neutrons in Oxygen

Neutrons with an energy of 14.1 Mev have been scattered in oxygen gas, and the recoil oxygen nuclei observed in a cloud chamber operated at a pressure of $\frac{1}{5}$ atmosphere. Recoils from elastically scattered neutrons were resolved from recoils due to inelastic scattering. The results indicate a strong asymmetry in the angular distribution of elastically scattered neutrons; the angular distribution has maxima at 0°, 80°, and 180° and minima at 60° and 130°. Within a factor of 2, the angular distribution for the inelastically scattered neutrons is symmetrical. The probability per unit energy interval that the oxygen nucleus will be left excited is about 5 times as large at 6-Mev excitation as at 12-Mev.