The Relative Biological Effectiveness of 138-Mev Protons as Compared to Cobalt-60 Gamma Radiation

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