Some Effects of 55-Mev Protons on Primates

Abstract

In previous studies the biological effects of 32-Mev, 55-Mev, and 138-Mev protons have been examined (1-3). At these energies the predominant mode of energy deposition results from direct ionization; nuclear processes that produce particles of high LET and high RBE (recoil nuclei, evaporation nucleons, etc.) provide less than 10 % of the total rad dose (4). In the experiments described in this communication, the biological effects produced by 400-Mev protons are explored. This energy is of interest because it is about the highest energy represented by significant numbers of protons in the space proton spectrum (5). Since at 400 Mev some 25 % of the total rad dose results from nuclear processes (4), the use of a monoenergetic source of these protons allows an evaluation of biological effects occurring when the relative concentration of the high-LET high-RBE particles equals or exceeds the maximum anticipated from irradiation with the space proton spectrum.