Promethium

Promethium is the only lanthanide with no stable isotopes. It is essentially absent from natural crustal rocks and can only be produced in trace amounts by artificial synthesis in nuclear reactors, so it has no industrial-scale practical use. Historically, its compounds were painted onto luminous dials for night-illuminated instruments and marine beacon lights, but these applications have largely been phased out for radiation-safety reasons. At present, promethium is used only in very small quantities in miniature radioisotope batteries and in nuclear-physics research.

Compounds of promethium, such as Pm2O3 (promethium(III) oxide) and PmCl3 (promethium trichloride), are prepared only in trace amounts in laboratories and as irradiated targets, used for materials irradiation studies and radioactive tracing; they do not enter any consumer product, and no large-scale industrial production exists.