Energy Spectra and Angular Distributions of Photoneutrons from Heavy Nuclei

The energy spectra of photoneutrons from the absorption of 22-Mev bremsstrahlung by silver and bismuth have been measured with nuclear emulsions. Comparisons are made between the observed photoneutron spectra and those predicted on the basis of a statistical nuclear model. Energy level densities are assumed proportional to $\exp \left[{\left(a\epsilon \right)}^{\frac{1}{2}}\right]$ and $\ln (\frac{A\epsilon }{20}+1)$, where $\epsilon$ is the excitation energy of the residual nucleus. The exponential form of the energy level density is in better agreement with the data than is the logarithmic form. However, for neutron energies greater than 4 Mev there are more photoneutrons observed than predicted by the exponential energy level density scheme.