Radiation chemistry of high-temperature (300–410 °C) water. Part 1.—Reducing products from gamma radiolysis

Abstract

Using gamma rays, and dilute solutions of radical scavengers, the G values of the primary reducing products from water, namely H₂, H and e^–_aq, were found to be 2.0, 0.3 and 0.4 at 400 °C, density 0.45 kg dm^–3, in marked contrast to the G values 0.4, 0.6 and 2.7, respectively, for liquid water at 25 °C. At 300 °C, density 0.75 kg dm^–3, G_H2 was similar to the value at 400 °C.

The high G value for hydrogen at 400 °C, coupled with low values for G_H and G_e^–aq suggests that, in contrast to reactions at room temperature, only a small fraction of the hydrogen is formed by the reaction together of the species H and e^–_aq in spur reactions. The molecular hydrogen is thought to be formed together with oxygen atoms mainly in unimolecular decomposition processes, e.g. H₂O*= H₂+ O.

The low dielectric constant of 8 at 400 °C compared with 80 at 25 °C is considered to be an important factor in determining the low G value for scavengeable electrons.

The low overall G value for water molecules ultimately decomposed at 400 °C and density 0.45 kg dm^–3 suggests a greater efficiency for the deactivation of excited molecules at that condition compared with liquid state at 25 °C.

A reaction mechanism is proposed which accounts for the observed product against dose curves when computer simulation of these is carried out.