Effects of Track Structure on the Ion Radiolysis of the Fricke Dosimeter

The chemistry of the Fricke dosimeter induced by low and high linear energy transfer (LET) radiation has been modeled using the stochastic IRT method, incorporating simulated ion tracks. Comparison of the results for track segments with experimentally determined differential yields shows excellent agreement for energetic electrons, and for nonrelativistic ions, including 1 H, 4 He, 12 C, and 20 Ne. There is a significant effect of particle type and energy on the response of the Fricke dosimeter, which reflects the competition between intra-track reaction of the radiation-induced radicals, diffusion, and scavenging. This competition is modified by changes in the ion track structure. Monte Carlo track structure simulations show that the radial energy loss profiles are similar for ions with the same velocity/charge ratio and that ∼40% of the energy is initially deposited within a water diameter of the track axis. The LET of the ionizing radiation is shown to be a poor parameter for characterizing the Fricke dosimeter and the observed chemistry is predicted more precisely by the square of the ratio of the particle charge to its velocity.