UF₆ is used for enrichment for several important reasons:
- Fluorine has only one stable isotope (F-19). This means that any mass difference between UF₆ molecules is entirely due to the uranium isotope (U-235 vs U-238). This is critical for mass-based separation methods.
- UF₆ is gaseous above 56 degrees C (at atmospheric pressure). Both the gaseous diffusion and gas centrifuge enrichment methods require the uranium compound to be in the gas phase, and hex achieves this at a conveniently low temperature.
- Fluorine has a low atomic weight (19), so it does not excessively increase the molecular mass or interfere with the separation process.