Three methods were used to determine the mobility of He in single crystals. These were permeation techniques, He release after soaking, and ion implantation. The permeation experiments gave diffusion and permeation activation energies which were equal to 0.34 to 0.39, and 0.63eV, respectively. The heat of solution was 0.29eV. Measurements of the gas release from crystals which had been implanted with 1016 He/cm2 at 300keV yielded an activation energy for gas release of 0.6eV. Diffusion in the undamaged crystal was interpreted as being due to the interstitial motion of the He atom.

Helium Solubility, Mobility, and Implantation Effects in Potassium Bromide. R.C.Wayne, W.Bauer: Physical Review B, 1972, 6[10], 3966-73