Abstract
Low-voltage (0.5-50 keV) electron beam irradiation of hydrated monolayers of Chinese hamster ovary (CHO) cells and isolated CHO nuclei induced single and double strand DNA scission. Gradient sedimentation techniques were used to assay DNA breakage in control populations having a $2\cdot 10^{8}$ number average molecular weight for native DNA and a $2\cdot 10^{7}$ number average for denatured DNA. Beam sensitivity responses, expressed as average cell rads/break, exhibited pronounced minima for beams that penetrated less than one third of the cell thickness and less than 1/20 of the nuclear thickness (i.e., top layer irradiation only). Almost half the total DNA population was degraded by these lower energy beams. A comparison of the breakage efficiency with that for Cs-137 γ-rays yielded estimates of the relative biological effectiveness (RBE) for low energy electrons (<2 keV) of between 1 and 3. The various results suggest that DNA molecules have multiple attachment...
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