Ray Type Dependence of Radiation Induced Surface Activation Phenomenon

The phenomenon named Radiation Induced Surface Activation (RISA) was discovered recently. It is a phenomenon involving the activation of surfaces of metallic oxides attributable for strong affinity for water. In this work, we examined wettability increase under irradiations with γ-ray and UV, as well as its degradation under non-irradiation condition by measuring the changes of water contact angle on oxide layers formed onto Zircaloy-4 plates. The water contact angle for the sample surface decreased gradually under irradiation, and increased gradually by darkroom storage after irradiation. The theoretical formula, which describes the development of the hydrophilic surface under irradiation and its stability, was fitted to the experimental results. It caused us to propose the existence of two kinds of hydrophilic factors in terms of stability, whose formation probabilities depend on the type of irradiation.