Modelling of linear energy transfer effects on track core processes in the radiolysis of water up to 300°C

Abstract

Deterministic diffusion–kinetic modelling of the radiolysis of water by low linear energy transfer (LET) radiation in terms of our recently formulated extended spur diffusion model (J. Phys. Chem., 1995, 99, 11464) has been applied to high LET radiation for 20 eV nm^-1<LET<70 eV nm^-1 up to 300°C for a cylindrical track. The calculations show that an increase in LET accelerates the decay of the radicals e^-_aq and OH, and the formation of the molecular products H₂ and H₂O₂ and increases the extents of the main track reactions. This results in changes in the chemical yields (g-values), i.e., a decrease in g(e^-_aq) and g(OH) and an increase in g(H₂) and g(H₂O₂), with increasing LET over the whole temperature range. For a given high LET an increase in temperature results in a marked increase in g(OH) and g(H₂), a small increase in g(e^-_aq) and a slight rise and fall in g(H₂O₂). These changes are largely accounted for by the different temperature dependences of the various radical–radical reactions. The temperature dependences of these g-values decrease with increasing LET. Reasonable agreement between modelling and experiment allows estimates to be made of the g-values for fast neutron radiolysis of water.