8. Thermal diffusion

Thermal diffusion uses heat transfer through a thin film of liquid or gas: UF ₆ is subjected to significant temperature differences to separate the isotopes ²³⁸ U and ²³⁵ U. The principle of the thermal diffusion column is to confine the mixture of isotopes to be separated in an annular space between two concentric cylinders heated to different temperatures.

The combination of diffusion movements and convection currents leads to the concentration of ²³⁵ UF ₆ and ²³⁸ UF ₆ molecules at the upper and lower ends of the column respectively. The separation...