RBE of HTO to 60Co gamma-rays for cell killing of a radioresistant E. coli harboring plasmid.

Radioresistant E. coli TGl harboring pUC 18 plasmid which was Ampicillin-resistant was exposed to 60Co gamma-rays or 3H beta-rays in saline to determine whether the relative biological effectiveness of 3H beta-rays is higher than one. After exposure to 60Co gamma-rays at a dose rate of 0.465 Gy/min, the D0 by colony formation was 145 Gy in the presence of Ampicillin in or absence from the agar medium; whereas, the D0 was calculated as 118 Gy with and without Ampicillin after exposure to 3H beta-rays at a dose rate of 0.431 Gy/min. The relative biological effectiveness established for 3H beta-rays to 60Co gamma-rays was 1.23. The reason for the higher effectiveness of 3H beta-rays as compared to the reference 60Co gamma-rays is discussed in terms of nascent 0 production.