Symbol Name Atomic Number Atomic Weight Group Number
Pm Promethium 61 145


Standard State: Solid at 298 K
Color: metallic

In 1902, Branner predicted the existence of an element between neodymium and samarium, and this was confirmed by Moseley in 1914.  In 1941, workers at Ohio State University irradiated neodymium and praseodymium with neutrons, deuterons, and alpha particles and produce several new radioactivities, which most likely were element 61. Wu and Segre, and Bethe, in 1942, confirmed the formation; however, chemical proof of the production of element 61 was lacking because of the difficulty in separating the rare earth elements from each other at that time. The element has applications as a beta source for thickness gages, and it can be absorbed by a phosphor to produce light.  Light produce in this manner can be used for signs or signals that require dependable operation.  Promethium shows promise as a portable X-ray unit.