Previous data on the diffusion of 22Na in single crystals were compared with new results on polycrystalline specimens (table 200). This indicated that the diffusion coefficients deduced for polycrystalline and monocrystalline samples were identical. It was concluded that Na did not diffuse via the grain-boundaries.

Diffusion of Na-22 in CsI Polycrytals. S.M.Klotsman, I.P.Polikarpova, A.N.Timofeev: Fizika Tverdogo Tela, 1970, 12[11], 3364-6