Whole-Body Irradiation of Primates with Protons of Energies to 400 Mev

Abstract

The effect of ionizing radiation on man is of vital interest to the space program. To further knowledge of these effects, a study involving whole-body exposures of primates to ionizing radiation has been initiated. The primate Macaca mulatta has been chosen as a suitable subject. Part of the study calls for irradiation of these animals by protons of various energies in the range 32 Mev to 2.3 Bev. This paper outlines the physical aspects and dosimetry of the whole-body irradiations with 32-Mev, 55-Mev, 138-Mev, 250-Mev, and 400-Mev protons, embracing the energy region where meson production can be considered negligible. The resultant biological effects are described elsewhere (1-8). At all energies the primates were placed in rotating cages during exposure to obtain a uniform distribution of dose. In the 32-Mev and 55-Mev exposures the protons did not penetrate completely through the primates, and the surface dose was used as the reference. At the higher energies the protons passed through the primates, and reasonably uniform body doses were obtained. Doses from 25 to 7000 rads were given, the dose rate varying with the different irradiation facilities. The 32-Mev and 55-Mev experiments were performed at the Oak Ridge Isochronous Cyclotron, the 138-Mev experiments at the Harvard University Synchrocyclotron, and the 250-Mev and 400-Mev experiments at the University of Chicago Synchrocyclotron. Dose-rate considerations made it necessary to use the three different facilities. At Harvard and Chicago multiple-Coulomb scattering was used to obtain the broad-beam profile required for the exposures; at Oak Ridge the beam optics system was able to defocus the beam to given an acceptable proton distribution. Exposures at each energy constituted an entity in themselves; however, the procedures followed are similar and are covered in detail only for the 32-Mev exposures. Beam measurements were made to determine the proton flux, and hence the time-