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) = 6.3 x 10-2 exp[-1.50(eV)/kT]

It was suggested that a vacancy mechanism was operating, although there was some evidence that a change in mechanism occurred with increasing temperature.

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