Mutation and inactivation of cultured mammalian cells exposed to beams of accelerated heavy ions

The induction of inactivation and mutation to thioguanine-resistance in cultured human diploid fibroblasts was studied after exposure to ionising radiations with LETs in the range 20 to 470 keV μm-1. Unique r.b.e. values were obtained for inactivation and mutation induction with nine different qualities of radiation. The plot of r.b.e. versus LET gave humped curves for both endpoints; r.b.e. maxima were in the LET range 90 to 200 keV μm-1 but the maximum r.b.e. value for mutation induction was almost twice that for inactivation. The accuracy of estimates of mutation induction are discussed with regard to possible selective effects against mutants during post-irradiation growth. (author)