RISK CROSS-SECTIONS AND THEIR APPLICATION TO RISK-ESTIMATION IN THE GALACTIC COSMIC-RAY ENVIRONMENT

Radiation risk cross sections (i.e, risks per particle fluence) are di scussed in the context of estimating the risk of radiation-induced can cer on long-term space flights from the galactic cosmic radiation outs ide the confines of the earth's magnetic field. Such quantities are us eful for handling effects not seen after low-LET radiation. Since appr opriate cross-section functions for cancer induction for each particle species are not yet available, the conventional quality factor is use d as an approximation to obtain numerical results for risks of excess cancer mortality. Risks are obtained for seven of the most radiosensit ive organs as determined by the ICRP [stomach, colon, lung, bone marro w (BFO), bladder, esophagus and breast], beneath 10 g/cm(2) aluminum s hielding at solar minimum. Spectra are obtained for excess relative ri sk for each cancer per LET interval by calculating the average fluence -LET spectrum for the organ and converting to risk by multiplying by a factor proportional to R(gamma) L Q(L) before integrating over L, the unrestricted LET. Here R(gamma) is the risk coefficient for low-LET r adiation (excess relative mortality per Sv) for the particular organ i n question. The total risks of excess cancer mortality obtained are 1. 3 and 1.1% to female and male crew, respectively, for a 1-year exposur e at solar minimum. Uncertainties in these values are estimated to ran ge between factors of 4 and 15 and are dominated by the biological unc ertainties in the risk coefficients for low-LET radiation and in the L ET (or energy) dependence of the risk cross sections (as approximated by the quality factor). The direct substitution of appropriate risk cr oss sections will eventually circumvent entirely the need to calculate , measure or use absorbed dose, equivalent dose and quality factor for such a high-energy charged-particle environment.