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The kinetics of recuperation following initial doses of 470 rads of 55 Mev protons and 350 rads of Co60 gamma radiation were investigated by means of the paired-dose method. By using semilog plots, recovery half-times of 4.85 plus or minus .85 days and 2.02 plus or minus .45 days were found after initial doses of the protons and Co60 gamma radiation, respectively.

The Harvard Synchrocyclotron Facility was the source of protons. A diagram of the experimental arrangement used for the irradiations with the cyclotron is shown in Fig. 1. Exposures were made in the primary proton beam which was defocused by a lead scatterer of 7.6 gm/cm2 placed at the exit of the cyclotron drift pipe. During exposure the mice were held in individual aluminum-screen cylindrical cages 3.8 cm in diameter by 10.2 cm long, stacked on 3.93-cm centers and oriented as shown in the diagram. The irradiations were performed with 4 mice at a time at a distance of 161 cm from the scatterer, with 6 mice at a time at 228 cm, and with

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