COMMENTARY Direct Biological Evidence for a Significant Neutron Dose to Survivors of the Hiroshima Atomic Bomb

In the past few years much physical evidence has accumu-lated that the A-bomb survivors at Hiroshima were exposed to significant doses of neutrons, in contrast to the predictions of the current DS86 dosimetry. We discuss some biological measure-ments of exchange-type chromosomal aberrations in survivors at Hiroshima, which also strongly imply that the survivors received a significant neutron dose. Specifically, the ratio of transloca-tions (an interchromosomal aberration) to pericentric inversions (intrachromosomal interarm aberration), the F value, was signifi-cantly smaller than would be expected from a y-ray exposure, and was consistent with the majority of the effective dose coming from neutrons. If this biological evidence and the previous physi-cal evidence are correct, the effective neutron dose at relevant locations at Hiroshima dominated the total effective dose, from which it may be concluded that (1)the risk coefficient for y rays may have been considerably overestimated, and (2) there is a possibility of deriving from the A-bomb data, with reasonable confidence limits, the relative biological effectiveness (RBE) for carcinogenesis by neutrons. o 1996by Radiation Research Societ