Radium (Ra)
Radium (Ra) is a radioactive metallic element with the atomic number 88 and atomic weight of 226.025. It is primarily found in uranium-bearing ores, such as uraninite (pitchblende) and carnotite, with significant deposits located in the Democratic Republic of the Congo, Canada, and the western United States. Radium-226, the most prevalent isotope, has a long half-life of 1,620 years and is a significant environmental concern due to its alpha and gamma radiation emissions. Historically, radium was used in cancer treatment and in luminous paints, although many health risks were associated with these applications, leading to serious health issues for workers exposed to radium. Today, its uses have largely been replaced by safer alternatives. Radium's chemical properties are similar to those of barium, and it is typically found in a chloride or bromide form for ease of handling. Understanding radium is critical due to its implications for environmental health and safety, particularly in areas associated with uranium mining and its decay products, such as radon.
Radium (Ra)
Where Found
The radium is found only in uranium-bearing ores. The most concentrated deposits of uranium are uraninite (pitchblende) and carnotite. The first deposits of pitchblende mined were in the Czech Republic, but later extensive deposits were found in the Democratic Republic of the Congo and in Canada’s Great Bear region. Carnotite is found in the sandstone of the western United States. The most significant U.S. source is in Utah. Oceans and other surface waters have concentrations of about 10-14 grams of radium per liter of water.
Primary Uses
Radium has few practical uses but has historical importance. Radium is used to treat some cancers. It is also used in and other industrial and scientific applications, and it has a role in the production of environmental radiation.
Technical Definition
Radium (symbol Ra) is a radioactive metallic element with atomic number 88 and atomic weight 226.025. Located in Group IIA of the periodic table, it is chemically similar to barium. Radium has twenty-five isotopic forms (mass numbers 206-230), all unstable. Pure radium is brilliant white, but it blackens as it rapidly oxidizes in air. Pure radium and its salts are luminescent. Radium has a melting point of 700° Celsius, a boiling point of 1,737° Celsius, and of 5.5 grams per cubic centimeter.
Description, Distribution, and Forms
Naturally occurring radium is predominantly the radium 226. With a of 1,620 years, it results from radioactive disintegration of uranium (U238). Because of its long half-life (4.5 billion years), U238 serves as an effectively constant source of Ra226. The radium and uranium are in equilibrium with each other in an undisturbed sample of ore, with a fixed ratio of 1:3,000,000.
Radium is an environmental concern as an intense source of alpha and gamma radiation, and its radioactive daughter, radon, is extremely dangerous at high levels. Radon is present in nearly all rock, is a component of air, and is ordinarily of little concern. However, when highly concentrated it is dangerous because of its alpha and because it decays successively to the particulate daughters polonium (Po218) and bismuth (Bi214). These radioactive isotopes have short half-lives, and when deposited in the lung their subsequent decay increases the risk of lung cancer. Thus, where uranium is found, radium is found, and in turn radon and its decay products. More than 50 percent of the U.S. population’s ordinary exposure to radiation is through radon.
Conventional uranium mining leaves nearly all the radium in the and the water used during extraction. An alternative uranium mining technique involves pumping chemical solutions into the ground to wash out uranium salts. In drilling for exploration and recovery, uranium- and radium-bearing formations are often disturbed. These are only some of the sources of radioactivity that are potentially dangerous unless properly treated and discarded.
History
In 1898, Marie Curie found that only those substances containing uranium or thorium emitted the penetrating radiation found earlier by Antoine-Henri Becquerel. Curie then found that the uranium-bearing pitchblende exhibited far more intense emissions than could be accounted for by the amount of uranium present. Marie and Pierre Curie were able to isolate a new radioactive element, polonium, by precipitation with bismuth. Further analysis of a much larger sample of pitchblende led them to use precipitation with barium to isolate an even more intense, rarer source of radiation—radium. The total world production of radium from 1898 to 1928 was only 500 grams.
The discovery of radium led directly to the theory of radioactivity. Radium was the principal high-intensity radioactive source used to study atomic and nuclear structure. It has since been supplanted by other radioisotopes that are safer and less costly.
Obtaining Radium
Radium is always found with uranium. The two primary uranium ores are pitchblende and carnotite. Pitchblende is a specific variety of uraninite, a form of uranium oxide. Pitchblende is dark and lustrous in appearance, and it is found principally in veins. Carnotite is a hydrous vanadate (vanadium-oxygen compound) of potassium and uranium, usually found in sandstone or other in the form of a loose or powder. The characteristic yellow color of carnotite, even in small amounts, stains sandstone. Carnotite is also the main source of the element vanadium. Other uranium-bearing ores are autunite, torbernite (chalcolite), and tyuyamunite.
Extraction of radium from these ores is very difficult. A barium compound is added to the to act as a carrier for the radium, since barium and radium are chemically similar. The barium and radium sulfates are removed from the remainder of the ore by precipitation. The sulfates are converted into sulfides or carbonates, which dissolve in hydrochloric acid. The barium chloride is then separated from the radium chloride by successive fractional crystallization. The pure metallic form is usually not isolated, since radium is more easily handled and used in chloride or bromide form, and its radioactive properties are unaffected by combination with other elements.
Uses of Radium
In the early twentieth century, radium was used for treatment of many types of cancer, the gamma radiation from radium’s daughter isotopes being the operative agent. It has been largely, though not completely, superseded by less costly, more powerful isotopes (particularly cobalt 60 and cesium 137) and accelerators.
Zinc sulfide in combination with a radium salt forms a luminescent material. Such luminous paints were used during the twentieth century until the 1970s to mark watch and meter dials, although radium was replaced by less hazardous promethium. Many young women employed in dial painting licked the tips of their brushes to produce a fine point, thus ingesting radium. In addition, water containing radium was often prescribed as a general tonic in the early part of the century. As a result of these practices, many people developed anemia, leukemia, or bone cancer. Radium, chemically similar to calcium, makes its way to the bone and is bound there. Decay of the radium or its daughter isotopes causes destruction of the bone marrow, and/or bone cancer.
Radium is used for industrial radiography. Similarly, radium is used for well-logging in prospecting for petroleum. Radium combined with beryllium produces a moderately intense source of neutrons.
Bibliography
Greenwood, N. N., and A. Earnshaw. “Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium.” Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, 1997.
Hanusa, Timothy P. "Radium." Encyclopedia Britannica, 21 Nov. 2024, www.britannica.com/science/radium. Accessed 21 Jan. 2025.
Harvie, David I. Deadly Sunshine: The History and Fatal Legacy of Radium. Tempus, 2005.
Hayter, Charles. An Element of Hope: Radium and the Response to Cancer in Canada, 1900-1940. McGill-Queen’s University Press, 2005.
Henderson, William. “The Group 2 Elements: Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium.” Main Group Chemistry, Royal Society of Chemistry, 2000.
Landa, Edward. Buried Treasure to Buried Waste: The Rise and Fall of the Radium Industry. Colorado School of Mines Press, 1988.
Mould, Richard F. A Century of X-Rays and Radioactivity in Medicine: With Emphasis on Photographic Records of the Early Years. Institute of Physics, 1993.
"Periodic Table—Radium." Resources on Isotopes, U.S. Geological Survey, 2004, wwwrcamnl.wr.usgs.gov/isoig/period/ra‗iig.html. Accessed 21 Jan. 2025.
Pflaum, Rosalynd. Grand Obsession: Madame Curie and Her World. Doubleday, 1989.
Segré, Emilio. From X-Rays to Quarks: Modern Physicists and Their Discoveries. W. H. Freeman, 1980.
Selman, Joseph. The Fundamentals of X-Ray and Radium Physics. 8th ed., C. C. Thomas, 1994.