Production of Gallium Isotopes in Copper by High-Energy Protons

Abstract

The production of ${\mathrm{Ga}}^{66}$, ${\mathrm{Ga}}^{67}$, and ${\mathrm{Ga}}^{68}$ in copper foils by high-energy protons has been determined by radiochemical techniques. Cross-section measurements were made for a series of copper foils ranging in thickness from 8 to 555 mg/${\mathrm{cm}}^{2}$ at each of the four proton energies 123, 254, 351, and 440 MeV. The thickness variations of the cross sections for all three isotopes were found to be consistent with the concept that these isotopes are formed by the capture in copper nuclei of alpha particles produced in primary interactions. Spectra of alpha particles with energies greater than 14 MeV which satisfactorily reproduced the experimental thickness variations were determined at each proton energy. These spectra were found to consist of a large number of evaporation alpha particles with a small forward-directed alpha-particle component. No evidence was found for the primary reaction ${\mathrm{Cu}}^{65}(p,{\ensuremath{\pi}}^{\ensuremath{-}}){\mathrm{Ga}}^{66}$; the contribution of such a reaction to the total ${\mathrm{Ga}}^{66}$ production cross section is less than one-third of a microbarn in natural copper at a proton energy of 440 MeV.