Gamma rays observed from 100-MeV protons interacting with 56Fe and 58Ni

Gamma radiation from 100-MeV protons incident on targets of ⁵⁸Ni and ⁵⁶Fe has been observed. Residual nuclei were identified by using the known γ rays. Some of the strongest γ rays observed involved residual nuclei equivalent to the target nucleus minus one to three α particles. These results can be understood on the basis of a pre-equilibrium stage involving an intranuclear nucleon-nucleon cascade followed by an evaporation process.