Question

$U^{235}$ and $U^{238}$ are separated by:

• A. sublimation
• B. gaseous diffusion
• C. electrolysis
• D. precipitation

Answer 1

Answer: (B)

gaseous diffusion

Since these are two isotopes of the same element, there will not be any chemical difference between them. That leaves us trying to separate them by physical (mechanical) means.

What has been traditionally done is to fluoridate the uranium and make uranium hexafluoride ($U{F}_6$) and then cool and spin it in a centrifuge.

These measures, when done and repeated, allow enrichment of the uranium by gaseous diffusion, which is all about lighter gases diffusing more quickly than gases that have more massive atoms or molecules as their makeup. Another industrial process for the separation of uranium isotopes is centrifugation.

Other laboratory or pilot scale methods are thermal diffusion, nozzle expansion, laser techniques and electromagnetic separation (the first method applied).