Photoneutron Cross Sections

The neutron yields resulting from photoneutron reactions have been measured as a function of betatron energy from threshold to 23 Mev for 22 elements. These yield curves have been analyzed by the photon difference method to give the total cross section $\sigma =({\sigma }_{\gamma ,n}+{\sigma }_{\gamma ,np}+2\mathrm{}{\sigma }_{\gamma ,2n})$ as a function of photon energy. Whenever possible, this cross section has been resolved into its components using threshold considerations and subsidiary data. Some general conclusions based on the new results are presented regarding the systematics of ($\gamma , n$) reactions.