THRESHOLD ENERGIES FOR THE FORMATION OF INTERMEDIATE-MASS FRAGMENTS IN PROTON-INDUCED REACTIONS

A compilation of the cross sections for production of Be-7, Na-24 and Mg-28 by bombarding U, Au and Ag targets with protons suggests two possible mechanisms for these reactions. One applies to the three targets and starts at a threshold energy of 0.8-1.0 MeV/nucleon. The other is observed only in the case of the U targets and has a much lower threshold energy of about 20 MeV, and is claimed to be due to the fission of the target residue.