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Jai Ganesh

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Registered: 2005-06-28

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Promethium

Promethium

Gist

Element 61 is called Promethium. Its chemical symbol is Pm. It is a man-made element, one of the rarest of the rare earth elements, and is radioactive.

Promethium's primary use is in research. It also finds applications in small atomic batteries, particularly for devices like pacemakers, guided missiles, and radios. Additionally, promethium is utilized in luminous paints and coatings, leveraging its phosphorescent properties. While not yet widespread, potential uses include portable X-ray sources and as a heat source for space applications.

Summary

Promethium is a chemical element; it has symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in the Earth's crust at any given time. Promethium is one of the only two radioactive elements that are both preceded and followed in the periodic table by elements with stable forms, the other being technetium. Chemically, promethium is a lanthanide. Promethium shows only one stable oxidation state of +3.

In 1902 Bohuslav Brauner suggested that there was a then-unknown element with properties intermediate between those of the known elements neodymium (60) and samarium (62); this was confirmed in 1914 by Henry Moseley, who, having measured the atomic numbers of all the elements then known, found that the element with atomic number 61 was missing. In 1926, two groups (one Italian and one American) claimed to have isolated a sample of element 61; both "discoveries" were soon proven to be false. In 1938, during a nuclear experiment conducted at Ohio State University, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not much recognized. Promethium was first produced and characterized at Oak Ridge National Laboratory in 1945 by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. The discoverers proposed the name "prometheum" (the spelling was subsequently changed), derived from Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans, to symbolize "both the daring and the possible misuse of mankind's intellect". A sample of the metal was made only in 1963.

The two sources of natural promethium are rare alpha decays of natural europium-151 (producing promethium-147) and spontaneous fission of uranium (various isotopes). Promethium-145 is the most stable promethium isotope, but the only isotope with practical applications is promethium-147, chemical compounds of which are used in luminous paint, atomic batteries and thickness-measurement devices. Because natural promethium is exceedingly scarce, it is typically synthesized by bombarding uranium-235 (enriched uranium) with thermal neutrons to produce promethium-147 as a fission product.

Details

Promethium (Pm) is a chemical element, the only rare-earth metal of the lanthanide series of the periodic table not found in nature on Earth.

Conclusive chemical proof of the existence of promethium, the last of the rare-earth elements to be discovered, was obtained in 1945 (but not announced until 1947) by American chemists Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell, who isolated the radioactive isotopes promethium-147 (2.62-year half-life) and promethium-149 (53-hour half-life) from uranium fission products at Clinton Laboratories (now Oak Ridge National Laboratory) in Tennessee. Identification was firmly established by ion-exchange chromatography. (Earlier investigators thought that they had found the element with atomic number 61 in naturally occurring rare earths and had prematurely called it illinium and florentium.)

Promethium-147 is effectively separated from the other rare-earth fission products by an ion-exchange method. Promethium has also been prepared by slow neutron bombardment of the isotope neodymium-146; the resulting isotope, neodymium-147, decays by electron emission to promethium-147. The metal itself was first prepared in 1963 by reduction of the fluoride, PmF3, with lithium. Two allotropic (structural) modifications of promethium are known: the α-phase is double close-packed hexagonal with a = 3.65 Å and c = 11.65 Å at room temperature. The β-phase is body-centred cubic with a = 4.10 Å (estimated) at 890 °C (1,634 °F).

All the isotopes of promethium are unstable; the longest-lived is promethium-145 (17.7-year half-life). Excluding nuclear isomers, a total of 38 radioactive isotopes of promethium are known. They range in mass from 126 to 163. The least stable isotope, promethium-128, has a half-life of one second. Because of the short half-lives of its isotopes, any promethium that might result from spontaneous fission of uranium in uranium ores would occur in infinitesimal concentrations.

The known uses of promethium are due to its radioactivity. Its soft beta-particle radiation can be converted to electricity in miniature batteries formed by sandwiching promethium between wafers of a semiconductor such as silicon; those batteries operate in extreme temperatures for up to five years. Other uses are as beta-radiation sources—e.g., in light sources that use phosphors to absorb beta radiation and convert it to visible light.

The physical and chemical properties of promethium are those of a typical rare earth. It is trivalent in its compounds and solutions, most of which are pink or rose.

Element Properties

atomic number  :  61
most stable isotope :  (145)
melting point  :  1,042 °C (1,908 °F)
boiling point  :  3,000 °C (5,432 °F) (estimated)
specific gravity  :  7.264 (at 24 °C [75 °F])
oxidation state  :  3.

Additional Information:

Appearance

A radioactive metal.

Uses

Most promethium is used only in research. A little promethium is used in specialised atomic batteries. These are roughly the size of a drawing pin and are used for pacemakers, guided missiles and radios. The radioactive decay of promethium is used to make a phosphor give off light and this light is converted into electricity by a solar cell.

Promethium can also be used as a source of x-rays and radioactivity in measuring instruments.

Biological role

Promethium has no known biological role.

Natural abundance

Promethium’s longest-lived isotope has a half-life of only 18 years. For this reason it is not found naturally on Earth. It has been found that a star in the Andromeda galaxy is manufacturing promethium, but it is not known how.

Promethium can be produced by irradiating neodymium and praseodymium with neutrons, deuterons and alpha particles. It can also be prepared by ion exchange of nuclear reactor fuel processing wastes.

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