Diffusion, Gaseous

Name:
Diffusion, Gaseous
Detailed information:
A technique used for separating the light isotope of uranium (²³⁵U) from the heavy isotope (²³⁸U). The uranium is allowed to diffuse through a series of microporous barriers whose apertures are of molecular dimensions, in the form of the gas uranium hexafluoride; this is a mix of ²³⁸UF₆ and ²³⁵UF₆ in a ratio code of 140:1. Because of the vastly greater number of the heavier molecules and the extremely small difference in their masses, the mix must pass through a barrier a great many times to obtain a high concentration of the 235 isotope. Assuming that the diffusion rate of two gases through a porous barrier is inversely proportional to the square root of their molecular weights, the ideal separation factor is the square root of the product M₁ times M₂, where M₂ is the molecular weight of ²³⁸UF₆, and M₁ that of ²³⁵UF₆. This method is still in use for uranium enrichment for nuclear fuel.