Inactivation of Bacterial Spores by Charged Particles

Abstract

Bacillus subtilis spores were bombarded with α-particles and heavy ions of carbon, nitrogen, and oxygen accelerated in the IPCR cyclotron. The maximum RBE was found at an unrestricted LET of about 120 keV·μm^-1 The effective inactivation cross section, S_eff, for α-particles increased with LET, reaching a stationary level of S_α^st, 0.145 μ². The analysis of the LET dependence revealed that several primary activations are required for producing one lethal-hit, within a very short length of the particle track. The value of S_α^st was lower than S_eff for heavy ions (0.22 ?? 0.26 μm²). This discrepancy may be due to a difference of the repair capacities of “strand-target” between α-particles and heavy-ion bombardments, or to existence of a target (s) which is sensitive for bombarding particles of extremely high LET, or to a long-range effects caused by such high-LET particles.