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SummaryThe frequency of micronuclei resulting from acentric chromosome and chromatid fragments induced by cobalt-60 gamma radiation and by ∼3 mev fast neutrons has been studied in the root-tip meristematic cells of Vicia faba. Roots irradiated with gamma-ray doses of 107 and 188 rads whilst in aerated water showed a greater micronuclear frequency than roots irradiated with similar doses in the absence of oxygen. The ratio of doses given in nitrogen and in air in order to produce the same micronuclear yield was found to be about 2·4. With roots irradiated with fast-neutron doses of 2·02, 4·95 and 9·94 rads the effect of oxygen is less marked, the nitrogen/air dose-ratio being about 1·4.For a given level of chromosome damage produced under conditions of aeration, neutron radiation was found to be about 10·5 times as effective as gamma-rays. Because of the quantitative difference in the response of the two types of radiation to the presence of oxygen, the relative biological efficiency of neutrons to gamma-rays under anoxic conditions would be about 18 to 1.
Evans et al. (Thu,) studied this question.