The diffusion of He at 1510 to 2470K was deduced from the rate of evolution of He upon heating B-doped crystals after slow neutron irradiation:

D(cm2/s) = 7.0 x 10-4 exp[-23.4(kcal/mol)/RT]

L.C.Luther, W.J.Moore: The Journal of Chemical Physics, 1964, 41[4], 1018-26