Mass spectrometry was used to monitor the permeation of He through monocrystalline membranes of the halide. The diffusion data were described by:

D (cm2/s) = 6.8 x 10-3 exp[-0.27(eV)/kT]

Rare-Gas Solubility and Diffusion in the Potassium Halides. R.C.Wayne: Physical Review B, 1973, 8[6], 2958-64