Dependence of the Oxygen Effect on the Energy of Fast Neutrons

Abstract

THE extent to which oxygen enhances radiation damage in biological systems is known to depend on the type of radiation used^1–4. Quantitatively, this effect may be represented by the oxygen enhancement ratio (OER), which is defined as the ratio between the doses of radiation required to produce equal degrees of damage in anoxic and oxygenated cells⁵. High values of the OER, that is, between 2.5 and 3.5, are usually observed for radiations of low mean linear energy transfer (LET), for example, X- or γ-rays, while with radiations of high mean LET, lower OER values are measured. In a series of experiments reported recently, the variation of the OER with LET has been investigated for deuterons and α-particles of different energies, using the capacity for clone formation as a test of the survival of cultured cells of human origin⁶. An experimental design which allowed selected segments of the tracks of these particles to pass through the cells enabled energy dissipation patterns with narrow LET distributions to be obtained. It was shown that the OER values decrease with increasing LET from 2.6 at 5.6 keV/µ of unit density tissue to a value of 2.05 at 61 keV/µ, followed by a more rapid decrease to 1.0 at 165 keV/µ.