Radium

Radium (pronounced /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 trace amounts in uranium ores. It is extremely radioactive. Its most stable isotope, ²²⁶Ra, has a half-life of 1602 years and decays into radon gas.

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Notable characteristics

The heaviest of the alkaline earth metals, radium is intensely radioactive and resembles barium in its chemical behavior. This metal is found in tiny quantities in the uranium ore pitchblende, and various other uranium minerals. Radium preparations are remarkable for maintaining themselves at a higher temperature than their surroundings, and for their radiations, which are of three kinds: alpha particles, beta particles, and gamma rays. Radium also produces neutrons when mixed with beryllium.

When freshly prepared, pure radium metal is brilliant white, but blackens when exposed to air (probably due to nitride formation). Radium is luminescent (giving a faint blue color), reacts violently with water and oil to form radium hydroxide and is slightly more volatile than barium. The normal phase of radium is a solid.

Applications

Some of the few practical uses of radium are derived from its radioactive properties. More recently discovered radioisotopes, such as ⁶⁰Co and ¹³⁷Cs, are replacing radium in even these limited uses because several of these isotopes are more powerful emitters, safer to handle, and available in more concentrated form.

When mixed with beryllium it is a neutron source for physics experiments.

Historical uses

Radium was formerly used in self-luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. More than 100 former watch dial painters who used their lips to shape the paintbrush died from the radiation. Soon afterward, the adverse effects of radioactivity became widely known. Radium was still used in dials as late as the 1950s. Although tritium's beta radiation is potentially dangerous if ingested, it has replaced radium in these applications.

During the 1930s it was found that workers exposure to radium by handling luminescent paints caused serious health effects which included sores, anemia and bone cancer. This use of radium was stopped soon afterward. This is because radium is treated as calcium by the body, and deposited in the bones, where radioactivity degrades marrow and can mutate bone cells. The litigation and ultimate deaths of five "Radium Girl" employees who had used radium-based luminous paints on the dials of watches and clocks had a significant impact on the formulation of occupational disease labor law.

Radium was also put in some foods for taste and as a preservative, but also exposed many people to radiation. Radium was once an additive in products like toothpaste, hair creams, and even food items due to its supposed curative powers. Such products soon fell out of vogue and were prohibited by authorities in many countries, after it was discovered they could have serious adverse health effects. (See for instance Radithor.) Spas featuring radium-rich water are still occasionally touted as beneficial, such as those in Misasa, Tottori, Japan.

Radium (usually in the form of radium chloride) is used in medicine to produce radon gas which in turn is used as a cancer treatment. The isotope ²²³Ra is currently under investigation for use in medicine as cancer treatment of bone metastasis.

History

Radium (Latin radius, ray) was discovered by Marie Skłodowska-Curie and her husband Pierre in 1898 in pitchblende from North Bohemia, in the Czech Republic (area around Jáchymov). While studying pitchblende the Curies removed uranium from it and found that the remaining material was still radioactive. They then separated out a radioactive mixture consisting mostly of barium which gave a brilliant green flame color and crimson carmine spectral lines which had never been documented before. The Curies announced their discovery to the French Academy of Sciences on 26 December 1898.

In 1902, radium was isolated as a pure metal by Curie and André-Louis Debierne through the electrolysis of a pure radium chloride solution by using a mercury cathode and distilling in an atmosphere of hydrogen gas.

Historically the decay products of radium were known as radium A, B, C, etc. These are now known to be isotopes of other elements as follows:

On February 4, 1936 radium E became the first radioactive element to be made synthetically.

One unit for radioactivity, the non-SI curie, is based on the radioactivity of ²²⁶Ra (see Radioactivity).

Occurrence

Radium is a decay product of uranium and is therefore found in all uranium-bearing ores. Radium was originally acquired from pitchblende ore from Joachimsthal, Bohemia (One metric ton of pitchblende yields 0.0001 grams of radium). Carnotite sands in Colorado provide some of the element, but richer ores are found in the Democratic Republic of the Congo and the Great Lakes area of Canada, and can also be extracted from uranium processing waste. Large uranium deposits are located in Ontario, New Mexico, Utah, Virginia, Australia, and in other places.

Compounds

Its compounds color flames crimson carmine (rich red or crimson color with a shade of purple) and give a characteristic spectrum. Due to its geologically short half life and intense radioactivity, radium compounds are quite rare, occurring almost exclusively in uranium ores.

• radium fluoride (RaF₂)
• radium chloride (RaCl₂)
• radium bromide (RaBr₂)
• radium iodide (RaI₂)
• radium oxide (RaO)
• radium nitride (Ra₃N₂)

See also radium compounds.

Isotopes

Radium has 25 different known isotopes, four of which are found in nature, with ²²⁶Ra being the most common. ²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra are all generated in the decay of either U or Th. ²²⁶Ra is a product of ²³⁸U decay, and is the longest-lived isotope of radium with a half-life of 1602 years; next longest is ²²⁸Ra, a product of ²³²Th breakdown, with a half-life of 6.7 years.

Radioactivity

Radium is over one million times more radioactive than the same mass of uranium. Its decay occurs in at least seven stages; the successive main products have been studied and were called radium emanation or exradio (this is radon), radium A (polonium), radium B (lead), radium C (bismuth), etc. Radon is a heavy gas and the later products are solids. These products are themselves radioactive elements, each with an atomic weight a little lower than its predecessor.

Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight with lead being the final product of disintegration.

The SI unit of radioactivity is the becquerel (Bq), equal to one disintegration per second. The curie is a non-SI unit defined as that amount of radioactivity which has the same disintegration rate as 1 gram of Ra-226 (3.7 x 10¹⁰ disintegrations per second, or 37 GBq).

Safety

Handling of radium has been blamed for Marie Curie's premature death.

• Radium is highly radioactive and its decay product, radon gas, is also radioactive. Since radium is chemically similar to calcium, it has the potential to cause great harm by replacing it in bones. Inhalation, injection, ingestion or body exposure to radium can cause cancer and other disorders. Stored radium should be ventilated to prevent accumulation of radon.

• Emitted energy from the decay of radium ionizes gases, affects photographic plates, causes sores on the skin, and produces many other detrimental effects.

Further reading

• Scientific American (Macklis RM, The great radium scandal. Sci.Am. 1993 Aug: 269(2):94-99)
• Clark, Claudia. (1987). Radium Girls: Women and Industrial Health Reform, 1910-1935. University of North Carolina Press. ISBN 0-8078-4640-6.
• Ken Silverstein, Harper's Magazine, November 1998; The radioactive boy scout: when a teenager attempts to build a breeder reactor - case of David Hahn who managed to secure materials and equipment from businesses and information from government officials to develop an atomic energy radiation project for his Boy Scout merit-badge.
• Decay chains (with some examples including Radium)
• Radium Girls

References

• Albert Stwertka (1998). Guide to the Elements - Revised Edition. Oxford University Press. ISBN 0-19-508083-1. 
• Radium. Los Alamos National Laboratory (Chemistry Operations) (December 18, 2003). Retrieved on 2007-12-25.
• Denise Grady. "A Glow in the Dark, and a Lesson in Scientific Peril", The New York Times, October 6, 1998. Retrieved on 2007-12-25. 
• Nanny Fröman (1 December 1996). Marie and Pierre Curie and the Discovery of Polonium and Radium. Nobel Foundation. Retrieved on 2007-12-25.