Angular Distributions and Yields of Neutrons from (p, n) Reactions

Angular distributions of neutrons from ($p, n$) reactions on Mg, Al, Cu, Mo, Ag, Ta, Au, Th, and U were measured for 23-Mev protons incident on thick targets. All angular distributions show peaks in the forward direction; except for Mg and Al, the $\frac{0°}{180°}$ intensity ratios vary from 5 to 15 for ∼13-Mev neutrons, and from 1.3 to 5 for ∼8-Mev neutrons. The Mg and Al high-energy data show minima and secondary maxima. Yield determinations indicate that the number of neutrons per nuclear reaction increases with atomic number from about 0.25 for Mg and Al to about 2.0 for most heavy elements and more than 4 for Th and U (probably due to fission). Temperatures of the neutron energy distributions are estimated; for the heavy elements at the backward angles, they are about 0.85 Mev at 3-Mev neutron energy, and about 1.9 Mev at 10-Mev neutron energy. It is concluded that direct interactions are of considerable importance in these reactions.