Electrochemical behaviour of gold and stainless steel under proton irradiation and active RedOx couples

Model experiments are reported where proton beams delivered by the cyclotron located at CERI (CNRS-Orléans) are used for irradiating AISI 316L/water and Au/water high purity interfaces with 6 MeV protons. The free exchange potentials at the interfaces are recorded as a function of time at room temperature in situ before, under, and after proton irradiation. The evolutions are compared to those calculated for the Nernst potentials associated with the radiolytic RedOx couples. It is shown how the comparison gives evidence that five radiolytic species – O2, H2O2, HO2−, HO2 and O2− – exchange electrons at the Au interfaces in a range of dose rates that vary over three orders of magnitudes, i.e. 0.0048 < dr(107 Gy h−1) < 4.8. The balance between the electron exchanges at Au interfaces is adjusted by the RedOx reactions associated with the above species. The free exchange potential reaches the same steady value for Au and AISI 316L interfaces irradiated at high doses, ≥2.5 × 107 Gy, (0.020 ± 0.025) V versus NHE. Such low values are the first ones to be reported. The HO2 and O2− radical disproportionations play a key role and control the potential at the interfaces under 6 MeV proton flux. This role is generally mostly overlooked for gamma irradiation.