The relative biological efficiency of single doses of fast neutrons and gamma-rays on Vicia faba roots and the effect of oxygen. Part I. Reduction of root growth.

Abstract

Primary roots of Vicia faba have been irradiated with fast neutrons of mean energy 3 Mev in air-saturated or air-free water at about 22 deg C, or by cobalt-60 gammarays in air-saturated water at about 19 deg C. The reduction in root growth in terms either of total growth in 10 days, or of minimum growth rate, has been taken as the measure of the biological effect of the radiation. The doseresponse curves with neutrons and gamma-rays in airsaturated water are of different shapes, so that there is no single value of relative biological efficiency. The rbe was about 15 for small doses and fell to a minimum of about 7 as the dose was increased. The form of the variation was consistent with what would be expected if reduction of root growih is principally due to chromosome damage. The presence of oxygen increases the radiosensitivity to fast neutrons; the ratio of equivalent doses in air-free and air-saturated water at 22 deg C is about 1.4. There is some indication that the oxygen factor is highest for small doses and falls steadily with increasing dose. (auth)