Explanatory notes
… of Explanatory Note to heading 28.44. This heading covers stable isotopes, that is, non‑radioactive isotopes and their … is separated from normal hydrogen in which it occurs at a level of 1 part in 6,500. (2) Heavy water , which is … part in 6,500. It is normally obtained as a residue of the electrolysis of water. Used as a source of deuterium, and in …