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   Pm

PROMETHIUM

(Gr. Prometheus, who stole fire from Heaven.)

Pm   at. wt. 147
     at. no. 61
     m.p.  ˜1080°C
     b.p.  2460°C
     sp. gr. ?.   
     valence 3.

Promethium was first predicted in 1902 by Branner to exist as an element between neodymium and samarium, and confirmed by Moseley in 1914. In 1941, workers at Ohio State University irradiated neodymium and praseodymium with neutrons, deuterons, and alpha particles, resp., and produced several new radioactivities, which most likely were those of 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 earths from each other at that time. In 1945, Marinsky, Glendenin, and Coryell made the first chemical identification by use of ion-exchange chromatography. Their work was done by fission of uranium and by neutron bombardment of neodymium. Searches for the element in nature have been fruitless, and it now appears that promethium is 9ompletely missing rrom the earth's crust. Fourteen isotopes of promethium, w'ith atomic masses from 141 to 154, are now known. Promethium-147, with a half-life of 2.64 yrs., is the most generally useful. Promethium-145 is the longest lived, with a half-life of 17.7 years. This isotope has a specific gravity of 940 curies per gram. It is a soft beta emitter; although no gamma rays are emitted, x-radiation can be generated when beta particles impinge on elements of a high atomic number, and great care must be taken in handling it. Promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity. Ion-exchange methods led to the preparation of about lOg of promethium from atomic reactor fuel processing wastes in early 1963. Little is yet generally known about the properties pf metallic promethium. Two or more allotropic modifications are thought to exist. The element has applications as a beta source for thickness gages, and it can be absorbed by a phosphor to produce light. Light produced in this manner can be used for signs or signals that require dependable operation; it can be used as a nuclear-powered battery by capturing light in photocells which convert it into electric current. Such a battery, using Pm147, would have a useful life of about 5 years. Promethium shows promise as a portable x-ray unit, and it may become useful as a heat source to provide auxiliary power for space probes and satellites. More than thirty promethium compounds have been prepared. Most are colored. Promethium-147 is avail- able to A.E.C. licensees at a cbst of about 50¢ per curie.

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