Time Dependent Accumulation of Hydrogen on Nickel Foils

As part of our investigation into the production of large area hydrogen free surfaces, we have studied the effectiveness of in vacuo (10-6 torr) high temperature (103 °C) heating of various materials suitable for use in ultra-cold neutron containers. Foils of the materials were resistively heated and subsequently measured for surface hydrogen concentration, using a nuclear resonant reaction technique, as a function of time. We were sucessful in cleaning the materials of hydrogen and several foils, for which we were able to heat to the point of evaporating their surface, remained relatively clean for several hours. For nickel we found that this slow recontamination rate is independent of foil length and inversely proportional to thickness. We conclude that hydrogen incident upon the cleaned material can stick to the surface and then diffuse into the interior and is probably resident on the internal grain boundary surfaces.