By measuring the He released during isothermal and ramp heating, it was possible to determine the diffusion coefficients of isolated He atoms. Consistent results were found only at homologous temperatures greater than about 0.60. The results could be described by:

D (cm2/s) = 1.3 x 100 exp[-1.35(eV)/kT]

V.Sciani, P.Jung: Radiation Effects, 1983, 78[1-4], 87-99