Research to determine the effects of defined numbers of α particles on individual mammalian cells is helpful in understanding risks associated with exposure to radon. This paper reports the first biological data generated using the single-particle/single-cell irradiation system developed at Pacific Northwest Laboratory. Using this apparatus, CHO-K1 cells were exposed to controlled numbers of 3.2 MeV α particles, and biological responses of individual cells to these irradiations were quantified. Chromosomal damage, measured by the induction of micronuclei, was evaluated after no, one, two, three or five particle traversals. Exposures of up to five α particles had no influence on the total numbers of cells recovered for scoring. With increased numbers of α particles there was a decrease in the ratio of binucleated to mononucleated cells of 3.5%/hit, suggesting that α particles induced dose-dependent mitotic delay. A linear hit-response relationship was observed for micronucleus induction: Micronuclei/binucleated cell = 0.013 ± 0.036 + (0.08 ± 0.013) × D, where D is the number of particles. When the estimated dose per α-particle traversal was related to the frequency of induced micronuclei, the amount of chromosomal damage per unit dose was found to be similar to that resulting from exposures to α particles from other types of sources. Approximately 72% of the cells exposed to five α particles yield no micronuclei, suggesting the potential for differential sensitivity in the cell population. Additional studies are needed to control biological variables such as stage of the cell cycle and physical parameters to ensure that each cell scored received the same number of nuclear traversals.

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