Promethium is a radioactive metal in the lanthanide series, which stretches from lanthanum (La) through lutetium (Lu).
The existence of the element was first predicted by Branner in 1902, a prediction confirmed by Moseley in 1914. The element was not found until the early 1940's when it was identified as a product of the irradiation of other rare earth elements.
The name is derived from the god Prometheus who, according to mythology, stole fire from heaven.
About 10 g of the metal were isolated in 1963 in the course of reprocessing fuels from nuclear reactors.
Pm does not occur naturally in the earth's crust, although it has been identified on the surface of star HR-465 in Andromeda.
Owing to their radioactivity, salts of the element luminesce with a pale blue or greenish glow. The element has been suggested for use in nuclear batteries in deep space probes.