Cellular effects of heavy charged particles

The human cell is rendered reproductively inactive by the passage of a single heavy ion through its nucleus when the heavy ion deposits energy at a rate greater than about 3500 MeV cm-1. This is demonstrated by the correlation of inactivation probability with nuclear area when cells having nuclei of different sizes are compared. This single-hit inactivation is irreversible and unmodifiable. The ion path length over which cells will be inactivated in this way is calculable from stopping power theory. Laboratory experiments in which three-dimensional human cell cultures were irradiated with high-energy nitrogen ions (3.9 GeV) at the Princeton Particle Accelerator confirm that cells are inactivated with maximum probability over the last 0.5 cm of the ion trajectory. This means that groups of adjacent cells in the ion path will be inactivated by a single ion with high probability. Organized systems of multiplying cells would be expected to amplify this spatially correlated effect of heavy ion irradiation. Abnormalities induced in Zea seedlings by heavy ion irradiation of seeds are consistent with the inactivation of embryonic cells in groups.