The surface migration coefficient of T which was physisorbed on monocrystalline Ni, without a chemisorbed sub-layer, was studied. The crystal orientation was chosen to be (111) because it offered the greatest concentration of adsorption sites per cm2. A clean sample surface was obtained by mechanical polishing or chemical etching, and subsequent ionic bombardment with high-purity Ar. Adsorbed T was produced by the introduction of a finite amount of T gas at the clean surface of the Ni sample. The T was used as a radioactive marker, and its 10keV β-radiation was measured. It was noted that T which was sorbed at 5K was quite immobile. After heating to a fixed temperature at 10 to 20K, the variation in the deposit profile as a function of time was used to determine the surface diffusion coefficient. Between 13 and 20K, the diffusivity varied from 10-5 to 1.5 x 10-4cm2/s, and an activation energy for diffusion of 0.2kcal/mol was deduced from the curve.

Superficial Migration of Tritium Physisorbed on Monocrystalline Nickel (111). M.Renard, D.Deloche: Surface Science, 1973, 35[2], 487-92