Effectofionizingradiationinducedbycoblet-60(Co-60)onEscherichiacolicellswasinvestigated.Acellularsurvivalcurveandmutantfrequenciesversusabsorbeddosesweredetermined.Theresultsshowedthatthelevelofbacteriainsurvivalcurvedecreaseto(2)LogwithgammaraydosesincreaseandD-valuewasequals(0.079)Gy.Afterirradiationthemutantfrequenciesincreasedwithdosesincrease,thegreatestmutantfrequencywas3.410-12(1mutationfor0.291012CFUfor150gofrifampicin)inducedby(1)Gy,whilethesmallerwas0.3910-12(1mutationfor3.411012CFUfor150gofrifampicin)inducedby(0.1)Gy