Various light- and medium-mass nuclei have been bombarded with 150-, 230-, 600-, and 960-MeV protons. Prompt $\gamma$ rays were measured with a Ge(Li) detector. A large number of lines in the $\gamma$-energy spectra correspond to the de-excitation of the first levels of $4n$ nuclei ($N=Z$ even). The dependence of this effect on the incident energy and the mass of the target is studied. The data are compared with recent pion-bombardment results.

• Received 20 March 1975

DOI:https://doi.org/10.1103/PhysRevLett.35.773