Radium

francium ← radium → actinium Ba ↑ Ra ↓ Ubn 88Ra Periodic table
Appearance
silvery white metallic
General properties
Name, symbol, number	radium, Ra, 88
Pronunciation	/ˈreɪdiəm/ RAY-dee-əm
Element category	alkaline earth metal
Group, period, block	2, 7, s
Standard atomic weight	(226)g·mol−1
Electron configuration	[Rn] 7s2
Electrons per shell	2, 8, 18, 32, 18, 8, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	5.5 g·cm−3
Melting point	973 K, 700 °C, 1292 °F
Boiling point	2010 K, 1737 °C, 3159 °F
Heat of fusion	8.5 kJ·mol−1
Heat of vaporization	113 kJ·mol−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 819 906 1037 1209 1446 1799
Atomic properties
Oxidation states	2 (strongly basic oxide)
Electronegativity	0.9 (Pauling scale)
Ionization energies	1st: 509.3 kJ·mol−1
	2nd: 979.0 kJ·mol−1
Covalent radius	221±2 pm
Van der Waals radius	283 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	nonmagnetic
Electrical resistivity	(20 °C) 1 µΩ·m
Thermal conductivity	(300 K) 18.6 W·m−1·K−1
CAS registry number	7440-14-4
Most stable isotopes
Main article: Isotopes of radium
iso NA half-life DM DE (MeV) DP 223Ra trace 11.43 d alpha 5.99 219Rn 224Ra trace 3.6319 d alpha 5.789 220Rn 226Ra ~100% 1601 y alpha 4.871 222Rn 228Ra trace 5.75 y beta− 0.046 228Ac

Radium (pronounced /ˈreɪdiəm/, RAY-dee-əm) 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. Its most stable isotope, ²²⁶Ra, has a half-life of 1601 years and decays into radon gas.

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.

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

Self-luminous white paint which contains radium on the face and hand of an old clock.

Radium was formerly used in self-luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. In the mid-1920s, a lawsuit was filed by five dying "Radium Girl" dial painters who had painted radium-based luminous paints on the dials of watches and clocks. The dial painters' exposure to radium caused serious health effects which included sores, anemia and bone cancer. 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.

During the litigation, it was determined that company scientists and management had taken considerable precautions to protect themselves from the effects of radiation, yet had not seen fit to protect their employees. Worse, for several years, the companies had attempted to cover up the effects and avoid liability by insisting that the Radium Girls were instead suffering from syphilis. This complete disregard for employee welfare had a significant impact on the formulation of occupational disease labor law.^[1]

As a result of the lawsuit, the adverse effects of radioactivity became widely known, and radium dial painters were instructed in proper safety precautions and provided with protective gear. In particular, dial painters no longer shaped paint brushes by lip. Radium was still used in dials as late as the 1960s, but there were no further injuries to dial painters. This further highlighted that the plight of the Radium Girls was completely preventable.

After the 1960s, radium paint was first replaced with promethium paint, and later by tritium bottles which continue to be used today. Although the beta radiation from tritium is potentially dangerous if ingested, it has replaced radium in these applications.

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.^[2] 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. In the U.S., nasal radium irradiation was also administered to children to prevent middle ear problems or enlarged tonsils from the late 1940s through early 1970s.^[3]

In 1909, the famous Rutherford experiment used radium as an alpha source to probe the atomic structure of gold. This experiment led to the Rutherford model of the atom and revolutionized the field of nuclear physics.

Radium (usually in the form of radium chloride) was used in medicine to produce radon gas which in turn is used as a cancer treatment, for example several of these radon sources were used in Canada in the 1920s and 1930s.^[4] 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 coming 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.^[5]

In 1910, 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.^[6]

Radium was first industrially produced in the beginning of the 20^th Century by Biraco, a subsidiary company of Union Minière du Haut Katanga (UMHK) in its Olen plant in Belgium. UMHK offered to Marie Curie her first gramme of radium.

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 in the US. Dr. John Jacob Livingood at the radiation lab at University of California, Berkeley was bombarding several elements with 5-MEV deuterons. He noted that irradiated bismuth emits fast electrons with a 5-day half-life ... the behavior of Radium E. ^[7][8][9]

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. (One ton of pitchblende typically yields about one seventh of a gram of radium).^[10] Radium was originally acquired from pitchblende ore from Joachimsthal, Bohemia, in the Czech Republic. 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 radium-containing uranium deposits are located in Canada (Ontario), the United States (New Mexico, Utah, and Virginia), Australia, and in other places.

Compounds

See also Category: Radium 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)

Isotopes

Radium (Ra) 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 naturally in the decay of either Uranium (U) or Thorium (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 5.75 years.^[11]

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 (now identified as 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 death due to aplastic anemia.

• 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.
• At the time of the Manhattan Project in 1944, the "tolerance dose" for workers was set at 0.1 microgram of ingested radium.^[12]

Further reading

• Macklis, R. M. (1993). "The great radium scandal". Scientific American 269 (2): 94–99. doi:10.1038/scientificamerican0893-94. PMID 8351514. 
• Clark, Claudia (1987). Radium Girls: Women and Industrial Health Reform, 1910–1935. University of North Carolina Press. ISBN ISBN 0-8078-4640-6. 

See also

• Decay chains
• Radium Girls

References

• Albert Stwertka (1998). Guide to the Elements - Revised Edition. Oxford University Press. ISBN 0-19-508083-1. 
• Denise Grady (October 6, 1998). "A Glow in the Dark, and a Lesson in Scientific Peril". The New York Times. http://www.nytimes.com/library/national/science/100698sci-radium.html. Retrieved 2007-12-25. 
• Nanny Fröman (1 December 1996). "Marie and Pierre Curie and the Discovery of Polonium and Radium". Nobel Foundation. http://nobelprize.org/nobel_prizes/physics/articles/curie/index.html. Retrieved 2007-12-25. 

External links

• WebElements.com - Radium (also used as a reference)
• Lateral Science - Radium Discovery
• Photos of Radium Water Bath in Oklahoma
• NLM Hazardous Substances Databank – Radium, Radioactive
• Reproduction of a 1942 comic book ad selling a "Radiumscope" to children