  In this paper, the role of air humidity on the iron corrosion under
irradiation is studied in the context of geological disposal of nuclear wastes.
The irradiation experiments are performed at room temperature using a 3 MeV
extracted proton beam with a 10 nA intensity. Different atmospheres are
studied: Humid air with a relative humidity (RH) fixed at 45 %, dry air and a
$^{15}N\_2$ atmosphere (45% RH). The hydrogen and oxygen distribution profiles
at the iron surface in contact with atmosphere are measured by using
respectively ERDA (Elastic Recoil Detection Analysis) and RBS (Rutherford
Backscattering Spectrometry) analysis. From these experiments it is clearly
demonstrated that the coupling of O$\_2$+H$\_2$O enhances iron oxidation
whereas for iron hydrogenation, humidity is sufficient whatever the atmosphere.
An interpretation is given, which is based on the reaction mechanisms and the
species formed by air ionisation.
