The impact parameter dependence of the inactivation of Bacillus subtilisspores has been measured using a heavy-ion mini-beam facility, which permits single-ion exposure of individual spores with a spatial accuracy of about 1 μm. The apparatus consists basically of a collimator and a microscope used to position the biological objects directly behind the collimator. Measurements were obtained for nickel, tin, and uranium ions at 1.4 MeV/u. for central hits the results show an inactivation probability of less than one with a continuous decrease in inactivation with increasing distance. Long-ranging effects which extend beyond the range of the δ electrons could not be confirmed.

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