The effect of linear energy transfer on the early, transient radiolytic oxygen depletion in the radiolysis of water by high-dose-rate irradiating protons

Abstract

Monte Carlo multi-track chemistry simulations were carried out to study, from a radiation chemistry perspective, the effect of “linear energy transfer” (LET) on the transient yields and concentrations of radiolytic oxygen consumption in the high dose-rate (~10<sup>7</sup> Gy/s) radiolysis of both pure air-saturated (0.25 mM O<sub>2</sub>) and oxygenated (30 µM O<sub>2</sub>) cell water, in the interval ~1 ps–10 µs. Our simulation model consisted of randomly irradiating water with single pulses of 5-MeV (LET ~ 8 keV/µm), 1.5-MeV (LET ~ 19.5 keV/µm), and 0.7-MeV (LET ~ 33 keV/µm) protons at 25 °C. Similar to what is observed with low-LET irradiation (~300-MeV protons, LET ~ 0.3 keV/µm), our calculations showed that, in pure aerated water, the concentration of depleted oxygen, [–O<sub>2</sub>], exhibits a pronounced maximum around ~0.1–0.2 μs for all three high-LET irradiating protons studied. This maximum increased markedly with increasing LET. As expected, the effect of adding competing scavengers of both hydrated electrons and •OH radicals on the radiolytic O<sub>2</sub> depletion in oxygenated cell water (a more bio-mimetic model of cells) irradiated by 5-MeV protons delivered at the same dose rate led to a marked decrease in the maximum of [–O<sub>2</sub>] around 1 μs. However, contrary to what is observed for low-LET irradiation, we found that the transient O<sub>2</sub> consumption is quite substantial under high-LET irradiation conditions. This is explained by the fact that, even though their underlying mechanism of action differs, high-LET particles affect radiolysis yields in a similar way to high dose rates.

Early and Transient Formation of Highly Acidic pH Spikes in Water Radiolysis under the Combined Effect of High Dose Rate and High Linear Energy Transfer

“…Herein, a multitrack irradiation model recently formulated in our laboratory was applied to describe the effects of high dose rates on the radiolysis of water by incident protons at ambient [22,[62][63][64] and elevated [65] temperatures. In short, this model consists of the random irradiation of water with single pulses of N incident monoenergetic protons, which simultaneously impact the water perpendicularly across the surface of a circle of radius R o (see Figure 1 of Alanazi et al [62]).…”

“…In this work, we use an extended multitrack chemistry version of our Monte Carlo computer code IONLYS-IRT [47] to simulate the radiolysis of pure, deaerated water at 25 • C by incident protons of various energies (i.e., of different LETs) under high-dose-rate conditions. This version has been described in detail elsewhere [22,62,64,65].…”