Gamma Rays Observed from 100-MeV Protons Interacting withFe56andNi58

Gamma radiation from 100-MeV protons incident on targets of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ has been observed. Residual nuclei were identified by using the known $\gamma$ rays. Some of the strongest $\gamma$ rays observed involved residual nuclei equivalent to the target nucleus minus one to three $\alpha$ 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.