Production of Protons by High Energyγ-Rays

The protons ejected from various nuclei by the gamma-ray beam of the 320-Mev Berkeley synchroton have been studied with a proportional counter telescope system. The energy distribution of the protons from carbon, copper, and lead from 7 Mev to 70 Mev at 90^∘{} was roughly proportional to 1E². The angular distribution was spherically symmetrical for 10-Mev protons and showed a pronounced forward maximum for protons of about 40 Mev. The cross section per nucleus for the ejection of 40-Mev protons was found to be proportional to Z.The experimental results indicate that protons above 30 Mev arise primarily from the interaction of the γ-ray with some small subunit of the nucleus rather than through the formation of an excited compound nucleus.