A Monte-Carlo step-by-step simulation code of the non-homogeneous chemistry of the radiolysis of water and aqueous solutions—Part II: calculation of radiolytic yields under different conditions of LET, pH, and temperature

Abstract

The importance of the radiolysis of water in the initial events following irradiation of biological systems has motivated considerable theoretical and experimental work in the field of radiation chemistry of water and aqueous systems. These studies include Monte-Carlo simulations of the radiation track structure and of the non-homogeneous chemical stage, which have been successfully used to calculate the yields of radiolytic species (H(·), (·)OH, H(2), H(2)O(2), e (aq) (-) , …). Most techniques used for the simulation of the non-homogeneous chemical stage such as the independent reaction time (IRT) technique and diffusion kinetics methods do not calculate the time evolution of the positions of the radiolytic species. This is a major limitation to their extension to the simulation of the irradiation of radiobiological systems. Step-by-step (SBS) simulation programs provide such information, but they are very demanding in term of computer power and storage capacity. Recent improvements in computer performance now allow the regular use of the SBS method in radiation chemistry simulations. In the first of a series of two papers, the SBS method has been reviewed in details and the implementation of a SBS code has been discussed. In this second paper, the results of several studies are presented: (1) the time evolution of the radiolytic yields from the formation of the radiation track to 10(-6) s; (2) the effect of pH on yields (pH ~ 0.4-7.0); (3) the effect of proton energy (and LET) on yields (300 MeV-0.1 MeV), and iv) the effect of the ion type ((1)H(+), (4)He(2+), (12)C(6+)) on yields. Nonbiological applications, i.e., the study of the temperature on the yields (about 25-300°C) and the simulation of the time evolution of G(Fe(3+)) in the Fricke dosimeter are also discussed.