Abstract
Some radiological properties of a 185 mev proton beam were studied with root-tips of bean and onion seedlings. The relationship between dose and number of abnormal metaphases was investigated at different depths of penetration in Lucite. The effect, found in the final part of the range of penetration,was higher than expected when the physical depth-dose to surface-dose ratio is considered. The difference is partly attributed to a variation of the relative biological efficiency. The enhancing effect of oxygen was studied at high and low energies. It was found to be nearly constant. The relative biological efficiency of 170 mev protons as compared with 180 kv roentgen rays for producing chromosome aberrations was found to be 0.7. The chromosome-breaking efficiencies of the secondary radiations from proton-irradiated tissue and brass were studied. The results indicate that the effects of secondary radiation may be neglected in therapeutic procedures.