Sticking coefficient of atomic hydrogen on graphite

The trapping of thermal hydrogen atoms in graphite has been measured by irradiating in graphite sample with a hydrogen atom beam containing tritium as tracer. After the irradiation the tritium activity of the surface layers was determined by a complete combustion and the sticking coefficient for thermal hydrogen atoms on graphite was measured as a function of the irradiation dose. At small doses the sticking coefficient is about 2% with a saturation at about 5.1018 atoms/cm2. The effect is discussed with respect to the tritium inventory of a fusion reactor using graphite as a first wall. (Auth.)