Mutation induction by accelerated heavy ions in bacteria.

Induction of lacI- forward mutations in Escherichia coli Ymcl and his(-)-->his+ reversions in Salmonella typhimurium TA102 was investigated after irradiation with heavy ions in the range of Z = 1-36. Particle specific energies (E) were in the range of 1-600 MeV/u. A strong dependence of the mutation induction cross-section (sigma m) on both particle energy and LETinfinity was observed. The results suggest that two different ranges of LETinfinity can be distinguished. In the range of high LETinfinity (> 100 keV/micron) sigma m increases with increasing specific particle energy if LETinfinity is kept constant (Fe ions as compared with carbon ions or alpha-particles). In the range of low LETinfinity (< 100 keV/micron) sigma m decreases with increasing energy (Ne ions as compared with He ions).