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