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 gamma 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.