Early dose assessment in criticality accidents.

Early estimation of dose is useful in the medical evaluation of severe radiation accidents. In a prior publication, lymphocyte depletion kinetics were shown to follow an exponential decline for gamma accidents in which the average whole-body dose was in the range 50 cGy < D < 8-10 Gy. In that study, the depletion rate constant was linearly related to dose, within the statistical variation of the historical hematological data. This simple technique has now been extended to include analysis of various types of criticality accidents (liquid process; water moderated systems; metallic systems). Lymphocyte depletion in high-level mixed gamma/neutron accidents is found to be approximately equal, at a given effective dose, to that for gamma accidents. This universality would indicate a neutron RBE for human lymphocytes close to unity. Furthermore, the technique appears to be insensitive to the shape of gamma and neutron spectra, therefore making it especially robust for initial, approximate dose estimation.