Comparative Biological Effects of Low Dose, Low Dose-Rate Exposures to Fission Neutrons from the JANUS Reactor or to sup 60 Co gamma Rays

摘要

The present status of long-term studies in neutron radiobiology using the JANUS reactor as the source of fission neutrons is summarized. A generally consistent pattern of response to neutrons is seen for both genetic and somatic end points. Dose protraction increases or augments the level of injury above that seen for single neutron doses. The responses to gamma -rays are more traditional. Either a reduction of the instantaneous dose rate or the distribution of a given total dose over a long sequence of small fractions will reduce the level of injury below that seen for single doses. For cellular and genetic end points, a supralinear response may occur at doses below 5 or 10 rad, but generally the end points at the systemic and organismic level show a near-linear response that is essentially independent of the pattern of exposure to total doses up to 10 or 20 rad of neutrons. Beyond 20 to 40 rad, the response becomes nonlinear, concave downward. In most of the data, responses to gamma -rays are linear and the linear coefficient declines as dose rate declines. This factor in combination with the near-invariant responses to neutrons at low doses leads to the observed increases in the RBE values from 2 to 20 for single doses to 8 to 35 for 60 weeks of exposure. 43 refs., 2 figs., 5 tables. (ERA citation 10:037748)