The R.B.E. of Different-energy Neutrons as Determined by Human Bone-marrow Cell-culture Techniques

Summary The effect of X-rays and different-energy neutrons on human bone-marrow cells was studied using two different cell-culture techniques-diffusion chamber (DC) growth and colony formation in vitro (CFU-C). Based on the survival of proliferative granulocytes in DC on day 13, the D0 value was 80 rad with X-rays, and 117 rad as measured by the CFU-C assay. The D0 values for neutrons depended on the radiation source and the energy level. The r.b.e. values, which dropped with increasing energy levels of mono-energetic neutrons, were (i) 0·44 MeV; DC 3·7, CFU-C 4·1; (ii) 6 MeV; DC 1·8, CFU-C 2·0; (iii) 15 MeV; DC 1·6, CFU-C 1·6; (iv) fission neutrons; DC 2·6, CFU-C 2·4.