Overview

Promethium is the only rare earth with no stable isotope; it is radioactive and vanishingly rare in nature, and its existence was confirmed only in 1945, when Jacob Marinsky, Lawrence Glendenin and Charles Coryell identified it among the fission products of uranium at Oak Ridge. Long predicted as the missing element 61, it had eluded every search in ordinary minerals precisely because it decays away. It is used in luminous paint and in miniature nuclear batteries. With no stable form and produced only in reactors or extracted from fission waste, promethium has few uses beyond luminous paint for dials and instruments, thickness gauges, and experimental atomic batteries that draw power from its steady radioactive decay.

Element 61 had a long false-start history before its genuine identification: research teams in the 1920s announced illinium, claimed by chemists at the University of Illinois, and florentium, claimed by Italian researchers in Florence, but neither claim survived closer scrutiny, and both are now regarded as mistaken readings of contaminated spectra rather than real detections. The correct identification had to wait for the machinery of the nuclear age, since promethium's complete absence of any stable isotope means it can only be produced artificially or in the vanishingly small quantities generated by the spontaneous fission of uranium in ordinary rock.