New radiation dosimetry estimates for Hiroshima and Nagasaki

Earlier studies of radiation dosimetry for atomic-bomb survivors at Hiroshima and Nagasaki attributed differences in leukemia mortality rates between the two cities to corresponding differences in neutron dosage levels. A high value of estimated neutron relative biological effectiveness (RBE, or level of biological damage caused by neutrons) was accordingly inferred. It now appears that the earlier dosimetry system produced estimates of neutron dose that are high by an order of magnitude. We have applied the new dose estimates to the leukemia data nd have found that the results do not support an inference of a large neutron RBE at low doses. Subsequent evidence, discussed here, tends to confirm our analysis within the prevailing uncertainties. As a result, the utility of data on atomic-bomb survivors in evaluating radiation safety standards is problematic