Before revision: The Uranium enrichment is difficult because the chemical properties of 235U and 238U are identical, so physical processes such as gaseous diffusion, gas centrifuge, laser, or the mass spectrometry must be used for isotopic separation based on small differences in mass.
After revision: The Uranium enrichment is difficult because chemical properties of 235U and 238U are identical, so physical processes such as gaseous diffusion, gas centrifuge, laser, or the mass spectrometry must be used for isotopic separation based on small differences in mass.