radium


radium
/ray"dee euhm/, n.
1. Chem. a highly radioactive metallic element whose decay yields radon gas and alpha rays. Symbol: Ra; at. wt.: 226; at. no.: 88.
2. a lustrous rayon or silk fabric constructed in plain weave and used in women's apparel, lining, and drapery.
[1895-1900; < NL, equiv. to L rad(ius) ray (see RADIUS) + -ium -IUM]

* * *

Chemical element, heaviest alkaline earth metal, chemical symbol Ra, atomic number 88.

It was discovered by Marie Curie and her husband, Pierre Curie, in 1898 and isolated by 1910. All its isotopes are radioactive (see radioactivity). Radium does not occur free in nature but occurs in natural ores such as pitchblende as a disintegration product of radioactive decay of heavier elements, including uranium. Chemically it is highly reactive and has valence 2 in all of its compounds. Its use in medicine (see radiation therapy; radiology; nuclear medicine) has declined because of its cost, and its use in consumer goods (to illuminate watch and clock hands and numbers, as well as instrument dials) was halted because it can cause radiation injury. It is still used for some radiography and as a source of neutrons.

* * *

 (Ra),  
 radioactive chemical element, heaviest of the alkaline-earth metals of main Group 2 (IIa) of the periodic table. Radium is a silvery white metal that does not occur free in nature.

      Radium was discovered (1898) by Pierre Curie, Marie Curie (Curie, Marie), and an assistant, G. Bémont, after Marie Curie had observed that the radioactivity of pitchblende was four or five times greater than that of the uranium it contained and not fully explained on the basis of radioactive polonium, which she had just discovered in pitchblende residues. The new, powerfully radioactive substance could be concentrated with barium, but because its chloride was slightly more insoluble it could be concentrated by fractional crystallization. The separation was followed by the increase in intensity of new lines in the ultraviolet spectrum and by a steady increase in the apparent atomic weight of the material until a value of 225.18 was obtained, remarkably close to the accepted value of 226.03. By 1902, 0.1 gram of pure radium chloride was prepared by refining several tons of pitchblende residues, and by 1910 Marie Curie and André-Louis Debierne had isolated the metal itself.

      Thirty-three isotopes of radium, all radioactive, are known; their half-lives, except for radium-226 (1,600 years) and radium-228 (5.8 years), are less than a few weeks. The long-lived radium-226 is found in nature as a result of its continuous formation from uranium-238 decay. Radium thus occurs in all uranium ores, but it is more widely distributed because it forms water-soluble compounds; the Earth's surface contains an estimated 1.8 × 1013 grams of radium.

      Since all the isotopes of radium are radioactive and short-lived on the geological time scale, any primeval radium would have disappeared long ago. Therefore, radium occurs naturally only as a disintegration product in the three natural radioactive-decay series (thorium, uranium, and actinium series). Radium-226 is a member of the uranium-decay series. Its parent is thorium-230 and its daughter radon-222. The further decay products, formerly called radium A, B, C, C′, C″, D, etc., are isotopes of polonium, lead, bismuth, and thallium.

      The chemistry of radium is what would be expected of the heaviest of the alkaline earths, but the intense radioactivity is its most characteristic property. One gram of radium-226 undergoes 3.7 × 1010 disintegrations per second, producing energy equivalent to 6.8 × 10−3 calories, sufficient to raise the temperature of a well-insulated sample at the rate of 1° C every 10 seconds. The practical energy release is even greater than this due to the production of a large number of short-lived radioactive decay products. The alpha particles emitted by radium may be used to initiate nuclear reactions.

      Radium's uses all result from its radiations. The most important use of radium was formerly in medicine, principally for the treatment of cancer by subjecting tumours to the gamma radiation of its daughter isotopes. In many therapeutic applications radium has been superseded by the less costly and more powerful artificial radioisotopes cobalt-60 and cesium-137. An intimate mixture of radium and beryllium is a moderately intense source of neutrons, used for scientific research and for well logging in geophysical prospecting for petroleum. For these uses, however, substitutes have become available. One of the products of radium decay is radon, the heaviest noble gas; this decay process is the chief source of that element.

      When concentrated, radium glows in the dark. Because of this property, it was once mixed with a paste of zinc sulfide, which could be excited by alpha particles, to make a self-luminescent paint for watch, clock, and instrument dials. During the 1930s it was found, however, that exposure to radium posed a serious hazard to health: a number of women who worked with the radium-containing luminescent paint during the 1910s and '20s had subsequently died. They had ingested considerable amounts of radium through the habit of licking the points of their brushes. Radium tends to concentrate in bone where alpha radiation interferes with red corpuscle production, so some of these women developed anemia and bone cancer. The practice of employing radium in luminescent coatings was halted in the early 1950s after the high toxicity of the material was recognized. Less hazardous alpha emitters have largely replaced radium. (The detection of exhaled radon provides a very sensitive test for radium absorption.)

      In the thorium-decay series of radioactive elements, two radium isotopes occur. They are found naturally in the mineral monazite: radium-228 (6.7-year half-life) and radium-224 (3.64-day half-life). One of their descendants, thallium-208, emits gamma radiation even more penetrating than that of bismuth-214; and, as a result of the complex sequence of half-lives, the gamma activity of freshly purified radium-228 increases for about four years and then steadily decreases. A fourth isotope, radium-223 (11.7-day half-life), occurs in the actinium-decay series.

      Metallic radium has high chemical reactivity. It is attacked by water with vigorous evolution of hydrogen and by air with the formation of the nitride. It occurs exclusively as the Ra2+ ion in all its compounds. The sulfate, RaSO4, is the most insoluble sulfate known, and the hydroxide, Ra(OH)2, is the most soluble of the alkaline-earth hydroxides. Its compounds are very similar to the corresponding barium compounds, making separation of the two elements difficult.

      In modern technology, radium is separated from barium by fractional crystallization of the bromides, followed by purification by ion-exchange techniques for removal of the last 10 percent of the barium. Radium metal may be prepared by electrolytic reduction of its salts.

atomic number
88
stablest isotope
226
melting point
about 700° C
boiling point
about 1,737° C
specific gravity
about 5
oxidation state
+2
electronic config.
[Rn]7s2

* * *


Universalium. 2010.

Look at other dictionaries:

  • RADIUM — En 1898, quelques mois après avoir découvert le polonium, Pierre et Marie Curie et leur collaborateur Gustave Bémont, poursuivant l’étude du fractionnement de la pechblende de Joachimsthal (aujourd’hui Jáchymov, en République tchèque), purent… …   Encyclopédie Universelle

  • Radium — (pronEng|ˈreɪdiəm) is a radioactive chemical element which has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black. Radium is an alkaline earth metal that is found in… …   Wikipedia

  • Radium — Ra di*um (r[=a] d[i^]*[u^]m), n. [NL., fr. L. radius ray.] (Chem.) An intensely radioactive metallic element found (combined) in minute quantities in pitchblende, and various other uranium minerals. Symbol, Ra; atomic weight, 226.4. Radium was… …   The Collaborative International Dictionary of English

  • Radium [1] — Radium, ein von dem Ehepaar Curie zuerst isoliertes Element, das mit Baryum große Aehnlichkeit zeigt. Durch Bestimmung des Chlorsilbers, das aus dem bei 100° getrockneten Radiumchlorid erhalten werden konnte, und unter der Annahme der Formel… …   Lexikon der gesamten Technik

  • Radium — Sn (radioaktives Erdalkalimetall) per. Wortschatz fach. (20. Jh.) Neoklassische Bildung. Entdeckt und bezeichnet von den französischen Physikern M. und P. Curie. Zu l. radius Strahl als das Strahlende .    Ebenso nndl. radium, ne. radium, nfrz.… …   Etymologisches Wörterbuch der deutschen sprache

  • Radium [2] — Radium. – Die Lehre von der atomaren Struktur der Elektrizität, die Elektronentheorie, und die aus ihr sich ergebende Definition der »korpuskularen Strahlungen« ebneten den Weg zu einem besseren, umfassenderen Verständnis der… …   Lexikon der gesamten Technik

  • Radium — Студийный альбом Ruoska Дата выпуска 22 марта 2005 Жанр Industrial metal Neue Deutsche Härte Лейбл Kråklund Records П …   Википедия

  • Radium — Radium, KS U.S. city in Kansas Population (2000): 40 Housing Units (2000): 19 Land area (2000): 0.041442 sq. miles (0.107335 sq. km) Water area (2000): 0.000000 sq. miles (0.000000 sq. km) Total area (2000): 0.041442 sq. miles (0.107335 sq. km)… …   StarDict's U.S. Gazetteer Places

  • Radium, KS — U.S. city in Kansas Population (2000): 40 Housing Units (2000): 19 Land area (2000): 0.041442 sq. miles (0.107335 sq. km) Water area (2000): 0.000000 sq. miles (0.000000 sq. km) Total area (2000): 0.041442 sq. miles (0.107335 sq. km) FIPS code:… …   StarDict's U.S. Gazetteer Places

  • Radĭum — Ra, chemisches Element, ist bisher nur als Begleiter des Urans in Mineralien aufgefunden worden, und zwar scheint der Gehalt der Gesteine an R. direkt von ihrem Urangehalt abhängig zu sein. Wahrscheinlich ist R. spurenweise überall in der festen… …   Meyers Großes Konversations-Lexikon

  • radium — RÁDIUM s.n. v. radiu. Trimis de LauraGellner, 13.09.2007. Sursa: DEX 98  RÁDIUM s.n. v. radiu. Trimis de LauraGellner, 13.09.2007. Sursa: DN …   Dicționar Român


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.