GENERATION OF ULTRAFAST TRANSIENT ACID SPIKES IN HIGH-TEMPERATURE WATER IRRADIATED WITH LOW LINEAR ENERGY TRANSFER RADIATION

Monte Carlo track chemistry simulations of the low linear energy transfer radiolysis of pure, deaerated liquid water have been used in combination with a spherical spur model to examine the effect of temperature on the in situ formation of H3O+ ions and the corresponding abrupt transient “acid-spike” response that is observed after irradiation. The magnitude and duration of this acid-spike effect were found to be a very sensitive function of temperature. At 25 °C, it is most intense at times less than ∼1 ns, with a pH of 3.3 remaining nearly constant. In contrast, at higher temperatures, there is an increasingly acidic but much shorter pH response. At 350 °C, the pH is around 1.7 on a time scale of ∼10 ps. At longer times, the pH gradually increases for all temperatures, ultimately reaching a constant value corresponding to the non-radiolytic, pre-irradiation concentration of H3O+ arising through water’s autoprotolysis at ∼1–10 μs following irradiation. It does not appear that this transient acid-spike ef...