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For nuclear batteries.
(Prometheus, who, according to mythology, stole fire from heaven) 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 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 doen by fission of
uranium and by neutron bombardment of neodymium.
Searches for the element on earth have been fruitless, and it now appears that
promethium is completely missing from the earth's crust. Promethium, however, has been
identified in the spectrum of the star HR465 in Andromeda. This element is being formed
recently near the star's surface, for no known isotope of promethium has a half-life
longer than 17.7 years. Seventeen isotopes of promethium, with atomic masses from 134 to
155 are now known. Promethium-147, with a half-life of 2.6 years, is the most generally
useful. Promethium-145 is the longest lived, and has a specific activity of 940 Ci/g.
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 10 g of premethium from atomic reactor fuel processing wastes in
early 1963. Little is yet generally known about the properties of metallic promethium. Two
allotropic modifications 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 147Pm, would have a useful life of about 5 years. Promethium shows promise
as a portable X-ray source, and it may become useful as a heat source to provide auxiliary
power for space probes and satellites. More than 30 promethium compounds have been
prepared. Most are colored.
Promethium-147 is available at a cost of about 50c/Ci.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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