Z-Dependence of the Cross Section for Photocapture by Nuclei

The number of neutrons evaporated by nuclei excited by $\mathrm{Li}(p,\gamma )$ photons is calculated along the compound nucleus formalism. It is found, for light nuclei, to be very small and to exhibit an odd-even alternation. From experimental cross sections for photoneutron production at 17 Mev, the cross section for photocapture by nuclei is deduced, and is found to be proportional to $Z$ within 25 percent. Material is presented for the application of the compound nucleus formalism to light nuclei, in particular a formula for the density of levels.