Energies of Neutrons from MsTh-D, La-D, Y-Be, and Sb-Be Photo-Neutron Sources

Abstract

The energies of neutrons from several neutron sources have been compared with those of neutrons of calculable energies from the $\mathrm{Li}(p,n)$ reaction by observing the maximum pulse heights of proton recoils in a hydrogen filled proportional counter. The values found for the average neutron energy from the various sources are: MsTh-D, 197\ifmmode\pm\else\textpm\fi{}10 kev; MsTh-Be, 827\ifmmode\pm\else\textpm\fi{}30 kev; Y-Be, 158\ifmmode\pm\else\textpm\fi{}5 kev; La-D, 151\ifmmode\pm\else\textpm\fi{}8 kev; and Sb-Be, 24\ifmmode\pm\else\textpm\fi{}3 kev.These values are consistently lower than those expected from the measured gamma-ray energies and the usually accepted photo-neutron thresholds. Better agreement could be obtained if the photo-neutron thresholds of deuterium and beryllium were taken as 2.23 and 1.68 Mev.The energies of the effective gamma-rays from ${\mathrm{Y}}^{88}$ and ${\mathrm{La}}^{140}$ are obtained from the neutron energies and are found to be 1.86 Mev and 2.53 Mev, respectively.