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| Atomic Number: | 91 | Atomic Symbol: | Pa | | Atomic Weight: | 231.0359 | Electron Configuration: | 2-8-18-32-20-9-2 | | Shells: | 2,8,18,32,20,9,2 | Filling Orbital: | 5f2 | | Melting Point: | 1600oC | Boiling Point: | oC | | Description: | Radioactive rare earth metal. |
History(Gr. protos, first) The first isotope of element 91 to be
discovered was 234Pa, also known as UX2, a short-lived member of the naturally
occuring 238U decay series. It was identified by K. Fajans and O.H. Gohring in
1913 and the named the new element brevium. When the longer-lived isotope 231-Pa
was identified by Hahn and Meitner in 1918, the name protoactinium was adopted
as being more consistent with the characteristics of the most abundant isotope.
Sody, Cranson, and Fleck were also active in this work. The name protoactinium
was shortened to protactinium in 1949. In 1927, Grosse prepared 2 mg of a white
powder, which was shown to be Pa2O5.
PropertiesLater, in 1934, from 0.1 g of pure Pa2O5 he isolated the element by two
methods, one of which was by converting the oxide to an iodide and "cracking" it
in a high vacuum by an electrically heated filament by the reaction: 2PaI5
--> 2Pa + 5I2.
Protactinium has a brigh metallic luster which it retains for some time in
air.
OccurenceThe element occurs in pitchblende to the extent of about 1
part 231Pa to 10 million of ore. Ores from Zaire have about 3 ppm.
IsotopesProtactinium has 20 isotopes, the most common of which is 231Pa with a
half-life of 32,700 years.
A number of protactinium compounds are known, some of which are colored.
HandlingThe element is superconductive below 1.4K. The element is a
dangerous material and requires precautions similar to those used when handling
plutonium.
ExtractionIn 1959 and 1961, it was announced that the Great Britain
Atomic Energy Authority extracted by a 12-stage process 125 g of 99.9%
protactinium, the world's only stock of the metal for many years to come. The
extraction was made from 60 tons of waste material at a cost of about $500,000.
Protactinium is one of the rarest and most expensive naturally occurring
elements.
CostsO.R.N.L. supplies promethium-231 at a cost of about $280/g.
HazardsThe elements is an alpha emitter (5.0 MeV) and is a radiological
hazard similar to polonium
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