Abstract :

Monte-Carlo simulations are used to calculate the primary yield of hydrogen peroxide ([G.sub.[H.sub.2][O.sub.2]]) of the radiolysis of pure, deaerated liquid water as a function of linear energy transfer (LET) of the incident radiation over the range ~0.3-100 keV [micro][m.sup.-1], at 25 and 300[degrees]C. The radiations include [1.sup][H.sup.+], [sup.2][H.sup.+], [sup.4][He.sup.2+], [sup.7][Li.sup.3+], and [sup.12][C.sup.6+] ions with energies from 0.17 MeV to 3.6 GeV. At 25[degrees]C, it is found that our [G.sub.[H.sub.2][O.sub.2]] values, calculated with protons of different initial energies, show a monotonic increase as a function of LET, in agreement with the commonly assumed expectation of an increase in molecular yields with increasing LET. Our calculated [H.sub.2][P.sub.2] yields at 300[degrees]C increase significantly faster with LET than do their corresponding 25[degrees]C values, showing that the temperature dependence of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] at higher LET is less than for low-LET radiation. We also report our results on the temporal variations of the [H.sub.2][O.sub.2] yields, in the interval ~1 x [10.sup.-13] - 1 x [10.sup.-6] s, at 25 and 300[degrees]C and for the different types of radiation considered. Finally, we find that for incident ions of equal LET 10 keV [micro][m.sup.-1], [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] decreases as the ion velocity increases, from protons (or deuterons) to carbon ions. These differences produced in [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] by changing the type of radiation are explained by the greater mean energy of secondary electrons from the higher velocity ions, which penetrate to a greater average distance from the actual particle track, with a corresponding decrease in molecular yields. Our calculated [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] values compare generally well with the experimental data available from the literature and are also in good accord with the predictions of deterministic diffusion-kinetic model calculations reported earlier. Key words: liquid water, radiolysis, primary yields, hydrogen peroxide ([H.sub.2][O.sub.2]), linear energy transfer (LET), accelerated protons and heavy ions, temperature, Monte-Carlo simulations.