Formation cross sections of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$, and ${}_{}{}^{24}{}_{}{}^{}\mathrm{Na}$ from tantalum, lead, and uranium targets irradiated with 3-, 10-, and 30-GeV protons have been measured. Similar measurements have been made with silver and gold targets at 30 GeV. At 10 and 30 GeV, the yield of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Na}$ increases regularly with target mass, whereas at lower energies plots of cross section versus target mass show minima. From the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ data, it seems probable that the excitation energy transferred to the struck nucleus by the incident particle reaches a maximum even for the heaviest nuclei at $E_p\le 10$ GeV. Very little, if any, additional nuclear excitation energy is gained by raising the incident proton energy above this figure.

• Received 9 January 1968

DOI:https://doi.org/10.1103/PhysRev.171.1297