The induction of sister chromatid exchanges (SCE) was examined in Chinese hamster ovary cells irradiated in the G1 phase of the cell cycle with α-particles from a plutonium-238 source. A significant increase in the frequency of SCE occurred with doses as low as 0.31 mGy (31 millirads). Although 30% of the cells showed an increased frequency of SCE at this dose, less than 1% of cell nuclei were actually traversed by an α-particle. A dose of approximately 2.0 Gy was necessary to produce a similar increase in SCE by X-rays. These results indicate that genetic damage may be induced by low doses of α-radiation in cell nuclei not actually traversed by an α-particle. This phenomenon may have important implications in the estimation of risks of such exposures.

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Supported by Grant PDT-440 from the American Cancer Society and by Grants CA-47542 and ES-00002 from the NIH.

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