Tracer-level diffusion studies were carried out on laboratory-prepared samples of pyrolytic carbon. Using a 228Th tracer, diffusion coefficients were measured perpendicular to the plane of deposition at 1600 to 2000C. The diffusion coefficient thorium perpendicular to the plane of deposition in granular, isotropic and laminar pyrolytic carbon was given by:

Granular:     D(cm2/s) =7.1 x 104exp[-152000/RT]

Isotropic:     D(cm2/s) = 15.5 exp[-114000/RT]

Laminar:     D(cm2/s) = 1.2 x 104 exp[-157000/RT]

H.K.Lonsdale, J.N.Graves: Journal of Applied Physics, 1967, 38[9], 3620-9