Chemical element, chemical symbol Rn, atomic number 86. The heaviest noble gas, it is colourless, odourless, tasteless, radioactive (see radioactivity), and almost completely unreactive (forming compounds only with fluorine). It is rare in nature because all its isotopes are short-lived and because radium, its source, is scarce. Radon seeps from certain soils and rocks (such as granite) into the atmosphere and can accumulate in poorly ventilated spaces near ground level, including house basements; in some regions of the world the use of such spaces is believed to increase the risk of lung cancer more than any other common factor except smoking. Radon is used in radiotherapy, radiography, and research.
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Radium 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, , has a half-life of 1602 years and decays into radon gas.
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.
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 is currently under investigation for use in medicine as cancer treatment of bone metastasis.
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:
See also Radium compounds.
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).