Radium

From New World Encyclopedia
88 franciumradiumactinium
Ba

Ra

Ubn
Ra-TableImage.png
periodic table
General
Name, Symbol, Number radium, Ra, 88
Chemical series alkaline earth metals
Group, Period, Block 2, 7, s
Appearance silvery white metallic
Atomic mass (226) g/mol
Electron configuration [Rn] 7s2
Electrons per shell 2, 8, 18, 32, 18, 8, 2
Physical properties
Phase solid
Density (near r.t.) 5.5 g/cm³
Melting point 973 K
(700 °C, 1292 °F)
Boiling point 2010 K
(1737 °C, 3159 °F)
Heat of fusion 8.5 kJ/mol
Heat of vaporization 113 kJ/mol
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 819 906 1037 1209 1446 1799
Atomic properties
Crystal structure cubic body centered
Oxidation states 2
(strongly basic oxide)
Electronegativity 0.9 (Pauling scale)
Ionization energies 1st: 509.3 kJ/mol
2nd: 979.0 kJ/mol
Atomic radius 215 pm
Miscellaneous
Magnetic ordering nonmagnetic
Electrical resistivity (20 °C) 1 µΩ·m
Thermal conductivity (300 K) 18.6 W/(m·K)
CAS registry number 7440-14-4
Notable isotopes
Main article: Isotopes of radium
iso NA half-life DM DE (MeV) DP
223Ra ? 11.43 d alpha 5.99 219Rn
224Ra ? 3.6319 d alpha 5.789 220Rn
226Ra trace 1602 y alpha 4.871 222Rn
228Ra syn 6.7 y beta- 0.046 228Ac

Radium (chemical symbol Ra, atomic number 88)

is a chemical element, which has the (see the periodic table).

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, Ra-226, has a half-life of 1,602 years and decays into radon gas.

Occurrence

Radium is a decay product of uranium and is therefore found in all uranium-bearing ores. It was originally acquired from pitchblende ore from Joachimsthal, Bohemia (7 metric tons of pitchblende yielding 1 gram of radium). Some of this element can be obtained from the carnotite sands of Colorado, but there are richer ores in the Democratic Republic of the Congo and the Great Lakes area of Canada. It can also be extracted from uranium processing waste. Large uranium deposits are located in Ontario (Canada), New Mexico and Utah (United States), Australia, and other parts of the world.

History

Radium (from the Latin word radius, meaning "ray") was discovered by Maria Skłodowska-Curie and her husband Pierre in 1898. The Curies were studying pitchblende, a variety of the uranium ore uraninite (mainly uranium dioxide, UO2) obtained from North Bohemia (area around Jáchymov). When they removed uranium from the ore, they found that the remaining material was still radioactive. They then separated out a radioactive mixture, consisting mostly of barium, which gave a brilliant red flame color and spectral lines that had never been documented before.

In 1902, Marie Curie and Andre Debierne isolated radium in its pure metallic form. Their method involved electrolysis of a solution of pure radium chloride, using a mercury cathode, and distillation the product in an atmosphere of hydrogen gas.

Historically, the radioactive decay products of radium were known as Radium A, B, C, and so forth. These are now known to be isotopes of other elements, as follows.

Radium emanation: radon-222
Radium A: polonium-218
Radium B: lead-214
Radium C: bismuth-214
Radium C1: polonium-214
Radium C2: thallium-210
Radium D: lead-210
Radium E: bismuth-210
Radium F: polonium-210

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

During the 1930s, it was found that workers exposed to radium when handling luminescent paints suffered from serious health problems, including sores, anemia, and bone cancer. This use of radium was stopped soon afterward. The reason for this problem is that the body treats radium as though it were calcium. Thus, radium becomes deposited in the bones, where radioactivity degrades the marrow and damages bone cells. Marie Curie's premature death has been attributed to her extensive work with radium.

Notable characteristics

The heaviest of the alkaline earth metals, radium is intensely radioactive and resembles Barium chemically. This metal is found (combined) in minute 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), corrodes in water to form radium hydroxide and is slightly more volatile than barium.

Isotopes

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

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)

See also radium compounds.

Applications

Some of the practical uses of radium are derived from its radiative properties. More recently discovered radioisotopes, such as cobalt-60 and caesium-137, are replacing radium in even these limited uses because several of these are much more powerful and others are safer to handle.

  • Formerly used in self-luminous paints for watches, clocks and instrument dials. More than 100 former watch dial painters who used their lips to shape the paintbrush died from the radiation. (See Radium Girls). Soon afterward, the adverse effects of radioactivity became widely known. Radium was still used in dials as late as the 1950's. Objects painted with this paint may still be dangerous, and must be handled properly. Currently, tritium is used instead of radium. Although tritium still carries some risks, it is considered by many to be safer than radium.
  • When mixed with Beryllium it is a neutron source for physics experiments.
  • 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.
  • Radium-223 is currently under investigation for use in medicine as cancer treatment of bone metastasis.
  • One unit for radioactivity, the non-SI curie, is based on the radioactivity of radium-226 (see Radioactivity).
  • At the turn of the 20th century radium was a popular 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 real and 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.

Precautions

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 the bone. Inhalation, injection, ingestion or body exposure to radium can cause cancer and other body 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)

References
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External links

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