title: Biophysical mechanism of radiation damage to mammalian cells by X- and gamma-rays.
abstract: Published information on the reproductive death in mammalian cells irradiated by a wide range of X- and gamma-ray energies has been re-analysed to extract intrinsic efficiencies of damage for the secondary electrons in transient equilibrium. On a log-log plot, a linear dependence on the track average l.e.t. and the average specific primary ionization is found, indicating that either serves as a good quality parameter. The soft X-ray data are consistent with this conclusion. Upon comparison with data for fast heavy ion irradiations, the average specific primary ionization is shown to be applicable independently of radiation type whereas track average l.e.t. is not. Furthermore it is revealed that electrons are most damaging near the end of their range but their efficiency is only about 10-20 per cent of that of fast ions at the same quality, possibly due to the influence of multiple scatter on the electron penetration depth. It is deduced that, for the dose rates involved, the damage by electrons is predominantly by intra-track action and not inter-track action. The results are consistent with the suggestion that optimum damage occurs when the mean free path between ionizations is equivalent to the strand separation in the double-stranded DNA.
mesh_terms: D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects*; D002588:Cesium Radioisotopes; D003037:Cobalt Radioisotopes; D006224:Cricetinae; D003412:Cricetulus; D004583:Electrons; D004735:Energy Transfer; D005720:Gamma Rays; D006367:HeLa Cells / Q000528:radiation effects; D006801:Humans
chemical_list: D002588:Cesium Radioisotopes; D003037:Cobalt Radioisotopes