Diffusion coefficients for thorium, obtained from specimens prepared by ion bombardment, were reported (table 17). Pyrolytic carbon was prepared by thermal decomposition of methane. Porosity determinations, using helium, indicated a pore-less structure. This was consistent with the measured crystallographic parameters (a = 2.46Å, c = 6.86Å) and density (2.2g/cm3). X-ray determinations, using a rocking-curve technique and flat specimens, revealed preferred-orientation indices of 80 to 90; based upon (002) reflections. The average distance between coherent domain boundaries (in the c-direction) was 150Å; determined by line-broadening of the (002) reflections.

Thorium Diffusion in Paralytic Carbon and Porous Graphite. Truitt, J., Alton, G.D., Blood, C.M.: Applied Physics Letters, 1963, 3[9], 150-2

Table 17

Thorium Diffusion in Graphite