Radium

Radium is a chemical element in the periodic table that has the symbol Ra and atomic number 88. Its appearance is almost pure white, but it blackens on exposure to air. 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 1602 years and decays into radon gas.

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 rays, beta rays, 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 a bit more volatile than barium.

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 watch, clock and instrument dials. This use was discontinued after the adverse affects of radioactivity were popularized. Objects painted with this paint may still be dangerous, and must be handled properly.
• Neutron source for high energy 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.
• The unit for radioactivity, the curie, is based on the radioactivity of radium-226 (see Radioactivity).

Radium, being one of the largest elements, is also used as a neutron source, usually when combined with francium.

History

Radium (Latin radius, ray) was discovered by Marie Curie and her husband Pierre in 1898 in pitchblende/uraninite from North Bohemia. 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 mostly consisting of barium which gave a brilliant red flame color and spectral lines which had never been documented before. In 1902 radium was isolated into its pure metal by Curie and Andre 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:

Radium emanation - radon-222

Radium A - polonium-228

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

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 (7 metric tons of pitchblende yields 1 gram of radium). Carnotite sands in Colorado provide some of the element, but richer ores are found in the Democratic Republic of the Congo, the Great Lake area of Canada and can also be extracted from uranium processing waste. Large uranium deposits are located in Ontario, New Mexico, Utah, 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 very short half life and intense radioactivity, radium compounds are quite rare, occurring almost exclusively in uranium ores.

Fluorides: radium (II) fluoride (RaF₂), Chlorides: radium (II) chloride (RaCl₂), Bromides: radium (II) bromide (RaBr₂), Iodides: radium (II) iodide (RaI₂), Hydrides: no data, Oxides: radium (II) oxide (RaO), Sulfides: no data, Selenides: no data, Tellurides: no data, Nitrides: no data

Isotopes

Radium has 25 different isotopes, four of which are found in nature, with radium-226 being the most common and stable. 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 Ra 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 1 million times more radioactive than the same amount of uranium. Its decay occurs in at least seven stages; the successive main products have been studied and are called radium emanation or exradio, radium A, radium B, radium C, etc. (The emanation is a heavy gas, the later products are solids.) These products are regarded as unstable 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 curie is 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).

Precautions

Radium is extremely radioactive and its decay product, radon is a radioactive gas. Since Ra is closely related to calcium, it has the potential to cause great harm by substituting it in bone. Inhalation, injection, or body exposure to radium can cause cancer and other body disorders. Stored radium should be ventilated to prevent build-up of radon.

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

Further reading

• Scientific American (Macklis RM, The great radium scandal. Sci.Am. 1993 Aug: 269(2):94-99)

References

• Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
• Los Alamos National Laboratory - Radium

External Links

• WebElements.com - Radium (also used as a reference)
• EnvironmentalChemistry.com - Radium (also used as a reference)
• Lateral Science - Radium Discovery