Monte Carlo track chemistry simulations of the radiolysis of water induced by the recoil ions of the 10B(n,α)7Li nuclear reaction. 1. Calculation of the yields of primary species up to 350 °C

Abstract

Monte Carlo track chemistry simulations were carried out to predict the yields (G-values) of all primary radical and molecular species produced in the radiolysis of pure, neutral water and 0.4 M sulfuric acid aqueous solutions by the recoil ions of the ¹⁰B(n,α)⁷Li nuclear reaction as a function of temperature from 25 to 350 °C. The calculations were performed individually for 1.47 MeV α-particles and 0.84 MeV lithium nuclei with “dose-average” linear energy transfer (LET) values of ∼196 and 225 eV nm⁻¹ at 25 °C, respectively. The overall yields were calculated by summing the G-values for each recoil ion weighted by its fraction of the total energy absorbed. In the calculations, the actual effective charges carried by the two helium and lithium ions (due to charge exchange effects) were taken into account and the (small) contribution of the 0.478 MeV γ-ray, also released from the ¹⁰B(n,α)⁷Li reaction, was neglected. Compared with data obtained for low-LET radiation (⁶⁰Co γ-rays or fast electrons), our computed yields for the ¹⁰B(n,α)⁷Li radiolysis of neutral deaerated water showed essentially similar temperature dependence over the range of temperatures studied, but with lower values for yields of free radicals and higher values for molecular yields. This general trend is a reflection of the high-LET character of the ¹⁰B(n,α)⁷Li recoil ions. Overall, the simulation results agreed well with existing estimates at 20 and 289 °C. For deaerated 0.4 M H₂SO₄ solutions, reasonable agreement between experiment and simulation was also found at room temperature. Nevertheless, more experimental data for both neutral and acidic solutions would be needed to better describe the dependence of radiolytic yields on temperature and to test our modeling calculations more thoroughly. Moreover, measurements of the (e_aq⁻ + e_aq⁻) reaction rate constant in near-neutral water would help us to determine whether the predicted non-monotonic inflections above ∼150 °C in G(H₂) and G(H₂O₂) are confirmed.