Neutron andβ/γ Radiolysis of Water up to Supercritical Conditions. 1. β/γYields for H2, H~· Atom, and Hydrated Electron

摘要

Yields for H_2, H~? atom, and hydrated electron production in β/γradiolysis of water have been measured from room temperature up to 400 C on a 250 bar isobar, and also as a function of pressure (density) at 380 and 400 C. Radiolysis was carried out using a beam of 2-3 MeV electrons from a van de Graaff accelerator, and detection was by mass spectrometer analysis of gases sparged from the irradiated water. N_2O was used as a specific scavenger for hydrated electrons giving N_2 as product. Ethanol-d_6 was used to scavenge H~? atoms, giving HD as a stable product. It is found that the hydrated electron yield decreases and the H~?atom yield increases dramatically at lower densities in supercritical water, and the overall escape yield increases. The yield of molecular H_2 increases with temperature and does not tend toward zero at low density, indicating that it is formed promptly rather than in spur recombination. A minimum in both the radical and H_2 yields is observed around 0.4 kg/dm~3 density in supercritical water.