The relative effects of direct and indirect actions of ionizing radiations on deoxyribonucleic acid

Abstract

The effectiveness of ionizing radiations in damaging the DNA particle, as determined by the number of primary ionizations in the volume occupied by each particle, which is required to reduce the intrinsic viscosity to half its original value has been determined over a range of concentrations from 0.01 to 100%. The different specimens of DNA employed differ considerably in sensitivity, but with each specimen the number of ionizations required is approximately constant from 1 to 100%. This means that over this range of concentration an ionization occurring in the water has the same effect as one within the DNA particle. The differences of sensitivity of the different samples are probably due to traces of protein contamination and disappear at the greater dilutions. The effects were independent of the dose rate and of the hardness of the radiations within the ranges used and identical effects were obtained with electrons and X-rays.