The diffusion of He at 800 to 1130K was deduced from the rate of evolution of He upon heating B-doped crystals after slow neutron irradiation:

D(cm2/s) = 1.8 x 10-3 exp[-14.0(kcal/mol)/RT],

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