The long-time chemistry occurring in the radiolysis of water with different types of radiation has been examined. Radiolytic processes were probed by determining the influence of added molecular hydrogen on the formation of hydrogen peroxide in the radiolysis of water with γ rays, 2 and 10 MeV protons, and 5 MeV helium ions. Homogeneous model calculations were used to obtain quantitative information about the yields of radicals and molecular products escaping the heavy ion tracks. The results show that the yields of radicals escaping from the tracks of 10 MeV protons is significant, whereas the corresponding yields with 2 MeV protons and 5 MeV alpha particles are much lower. The addition of molecular hydrogen has a negligible effect on the formation or consumption of hydrogen peroxide in the radiolysis of water using heavy ions with a high linear energy transfer rate, LET. This result is contrary to the predictions of a homogeneous model and suggests that the long-time chemistry of water is not well-known or that a homogeneous model cannot be applied to high LET radiation. There is also the possibility that a significant yield of an oxidizing species is produced at high LET.

Molecular hydrogen yields have been measured in the γ radiolysis of aqueous solutions with a wide variety of scavengers of the hydrated electron and its precursors. A decrease in molecular hydrogen yield with increasing scavenging capacity of the hydrated electron is found with all solutes. Scavengers with particularly high rate coefficients for reaction with the precursors to the hydrated electron compared to the hydrated electron, such as selenate and to a lesser extent molybdate, show a more rapid decrease in hydrogen yields with increasing scavenging capacity than is observed with the other solutes. The yield of molecular hydrogen is better parametrized by the scavenging capacity for the precursors to the hydrated electron than by the scavenging capacity for the hydrated electron. Good scavengers of precursors to the hydrated electrons do not exhibit a "nonscavengable" hydrogen yield in the high scavenging capacity limit. These results suggest that the previously accepted "nonscavengable" yield of molecular hydrogen is due to precursors of the hydrated electron and it can be lowered with appropriate scavengers.

The radiation chemical yields of hydrogen peroxide in water at neutral pH have been determined with protons, helium ions, and carbon ions at energies of a few to 30 MeV. The long-time yields of hydrogen peroxide increase with increasing linear energy transfer, LET, for protons and helium ions, but it decreases for carbon ions due to higher order reactions within the particle track. However, the maximum increase in hydrogen peroxide yields is only about 50% from γ rays (LET = 0.2 eV/nm) to helium ions (LET = 156 eV/nm). Methanol was used as an OH radical scavenger in order to probe the temporal dependence of hydrogen peroxide formation. The differences in the time dependence of the formation of hydrogen peroxide with various ions are discussed and compared to that observed with γ rays.