Theory of RBE for Heavy Ion Bombardment of Dry Enzymes and Viruses

Abstract

The response of dry enzymes and viruses to heavy ion bombardment may be predicted from their response to γ-irradiation (and no further knowledge of their size and structure). The molecules are approximated as point particles whose response to ionization is the same for heavy ion bombardment as for γ-rays. From the δ-ray distribution formula and an extrapolated range-energy relation for electrons, the radial distribution of secondary ionization energy may be found. Under this dosage distribution the inactivation probability may be found as a function of radial distance from the ion's path, and then may be integrated over all space to find the inactivation cross section. These essentially geometric theoretical relations between the γ-ray D37 values and the inactivation cross section constitute a complete theory of RBE for the heavy ion bombardment of these substances. Theoretical relationships agree with published experimental values to an average deviation of 15 % for the enzymes , β-galactosidase and trypsin, and for T-1 and φX-174 bacteriophages, when bombarded with ions ranging from Z = 1 to 18, at ion speeds of 0.07 c (2.3 MeV/nucleon) and 0.145 c (10 MeV/nucleon).