28 radionuclides produced by spallation of natural copper by 720 MeV $\alpha$ particles were investigated by direct $\gamma$ counting of irradiated targets. Although the isobaric yield distributions and mass yield curve are similar in many respects to those found in proton spallation, a suppression of yields of neutron deficient products is observed. Several interpretations of this latter phenomenon are critically discussed.

NUCLEAR REACTIONS $\mathrm{Cu}(\alpha , \mathrm{spallation})$, $E=410, 720$ MeV; measured formation cross sections 28 radionuclides, direct $\gamma$ counting, natural target.

• Received 28 March 1974

DOI:https://doi.org/10.1103/PhysRevC.10.150