Радий: Химиялық элемент және қасиеттері

the chemical element

Radium is a chemical element; it has symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery white, but it readily reacts with nitrogen (rather than oxygen) upon exposure to air, forming a black surface layer of radium nitride (Ra3N2). All isotopes of radium are radioactive, the most stable isotope being radium 226 with a half life of 1,600 years. When radium decays, it emits ionizing radiation as a by product, which can excite fluorescent chemicals and cause radioluminescence. Radium, in the form of radium chloride, was discovered by Marie and Pierre Curie in 1898 from ore mined at Jáchymov. They extracted the radium compound from uraninite and published the discovery at the French Academy of Sciences five days later. Radium was isolated in its metallic state by Marie Curie and André Louis Debierne through the electrolysis of radium chloride in 1911. In nature, radium is found in uranium ores and (to a lesser extent) thorium ores in trace amounts as small as a seventh of a gram per ton of uraninite. Radium is not necessary for living organisms, and its radioactivity and chemical reactivity make adverse health effects likely when it is incorporated into biochemical processes because of its chemical mimicry of calcium. as of 2014, other than its use in nuclear medicine, radium has no commercial applications. Formerly, from the 1910s to the 1970s, it was used as a radioactive source for radioluminescent devices and also in radioactive quackery for its supposed curative power. These applications have become obsolete owing to radium's toxicity; as of lc=y, less dangerous isotopes (of other elements) are instead used in radioluminescent devices.

Radium is the heaviest known alkaline earth metal and is the only radioactive member of its group. Its physical and chemical properties most closely resemble its lighter congener, barium. Pure radium is a volatile silvery white metal, although its lighter congeners calcium, strontium, and barium have a slight yellow tint. Like barium and the alkali metals, radium crystallizes in the body centered cubic structure at standard temperature and pressure: the radium–radium bond distance is 514.8 picometers. Radium has a density of 5.5 g/cm3, higher than that of barium, again confirming periodic trends; the radium barium density ratio is comparable to the radium barium atomic mass ratio,
due to the two elements' similar crystal structures.

Radium, like barium, is a highly reactive metal and always exhibits its group oxidation state of +2. For this reason, the standard electrode potential for the half reaction Ra2+ (aq) + 2e− → Ra (s) is −2.916 V, even slightly lower than the value −2.92 V for barium, whereas the values had previously smoothly increased down the group (Ca: −2.84 V; Sr: −2.89 V; Ba: −2.92 V). One kilogram of the Earth's crust contains about 900 picograms of radium, and one liter of sea water contains about 89 femtograms of radium.

Radium was discovered by Marie Skłodowska Curie and her husband Pierre Curie on 21 December 1898, in a uraninite (pitchblende) sample from Jáchymov. While studying the mineral earlier, the Curies removed uranium from it and found that the remaining material was still radioactive. In July 1898, while studying pitchblende, they isolated an element similar to bismuth which turned out to be polonium. They then isolated a radioactive mixture consisting of two components: compounds of barium, which gave a brilliant green flame color, and unknown radioactive compounds which gave carmine spectral lines that had never been documented before. The Curies found the radioactive compounds to be very similar to the barium compounds, except they were less soluble. This discovery made it possible for the Curies to isolate the radioactive compounds and discover a new element in them. The Curies announced their discovery to the French Academy of Sciences on 26 December 1898. The naming of radium dates to about 1899, from the French word radium, formed in Modern Latin from radius (ray): this was in recognition of radium's power of emitting energy in the form of rays. In September 1910, Marie Curie and André Louis Debierne announced that they had isolated radium as a pure metal through the electrolysis of pure radium chloride (RaCl2) solution using a mercury cathode, producing radium–mercury amalgam. This amalgam was then heated in an atmosphere of hydrogen gas to remove the mercury, leaving pure radium metal. Later that same year, E. Eoler isolated radium by thermal decomposition of its azide, Ra(N3)2. The general historical unit for radioactivity, the curie, is based on the radioactivity of 226Ra: it was originally defined as the radioactivity of one gram of radium 226, but the definition was later slightly refined to be 3.7.

Radium was formerly used in self luminous paints for watches, nuclear panels, aircraft switches, clocks, and instrument dials. A typical self luminous watch that uses radium paint contains around 1 microgram of radium. Their exposure to radium caused serious health effects which included sores, anemia, and bone cancer. 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 licked paint brushes to shape them (which caused some ingestion of radium salts). Radium was still used in dials as late as the 1960s, but there were no further injuries to dial painters. This highlighted that the harm to the Radium Girls could easily have been avoided. From the 1960s the use of radium paint was discontinued. In many cases luminous dials were implemented with non radioactive fluorescent materials excited by light; such devices glow in the dark after exposure to light, but the glow fades. These had the added advantage of not degrading the phosphor over time, unlike radium. Tritium emits very low energy beta radiation (even lower energy than the beta radiation emitted by promethium) which cannot penetrate the skin, rather than the penetrating gamma radiation of radium, and is regarded as safer. Clocks, watches, and instruments dating from the first half of the 20th century, often in military applications, may have been painted with radioactive luminous paint. They are usually no longer luminous; however, this is not due to radioactive decay of the radium (which has a half life of 1600 years) but to the fluorescence of the zinc sulfide fluorescent medium being worn out by the radiation from the radium. The appearance of an often thick layer of green or yellowish brown paint in devices from this period suggests a radioactive hazard. The radiation dose from an intact device is relatively low and usually not an acute risk; but the paint is dangerous if released and inhaled or ingested.

Radium was once an additive in products such as 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 or Revigator types of "radium water" or "Standard Radium Solution for Drinking".)

Radium (usually in the form of radium chloride or radium bromide) was used in medicine to produce radon gas, which in turn was used as a cancer treatment; for example, several of these radon sources were used in Canada in the 1920s and 1930s. However, many treatments that were used in the early 1900s are not used anymore because of the harmful effects radium bromide exposure caused. Some examples of these effects are anaemia, cancer, and genetic mutations. as of 2011, safer gamma emitters such as 60Co, which is less costly and available in larger quantities, are usually used to replace the historical use of radium in this application. Howard Atwood Kelly, one of the founding physicians of Johns Hopkins Hospital, was a major pioneer in the medical use of radium to treat cancer. His first patient was his own aunt in 1904, who died shortly after surgery. Kelly was known to use excessive amounts of radium to treat various cancers and tumors. As a result, some of his patients died from radium exposure. His method of radium application was inserting a radium capsule near the affected area, then sewing the radium "points" directly to the tumor. As of 2015, safer and more available radioisotopes are used instead. In the first extraction of radium, Curie used the residues after extraction of uranium from pitchblende. The uranium had been extracted by dissolution in sulfuric acid leaving radium sulfate, which is similar to barium sulfate but even less soluble in the residues. The residues also contained rather substantial amounts of barium sulfate which thus acted as a carrier for the radium sulfate. The first steps of the radium extraction process involved boiling with sodium hydroxide, followed by hydrochloric acid treatment to minimize impurities of other compounds. The remaining residue was then treated with sodium carbonate to convert the barium sulfate into barium carbonate (carrying the radium), thus making it soluble in hydrochloric acid. After dissolution, the barium and radium were reprecipitated as sulfates; this was then repeated to further purify the mixed sulfate. Some impurities that form insoluble sulfides were removed by treating the chloride solution with hydrogen sulfide, followed by filtering. When the mixed sulfates were pure enough, they were once more converted to mixed chlorides; barium and radium thereafter were separated by fractional crystallisation while monitoring the progress using a spectroscope (radium gives characteristic red lines in contrast to the green barium lines), and the electroscope. After the isolation of radium by Marie and Pierre Curie from uranium ore from Jáchymov, several scientists started to isolate radium in small quantities. Later, small companies purchased mine tailings from Jáchymov mines and started isolating radium. In 1904, the Austrian government nationalised the mines and stopped exporting raw ore. Until 1912 when radium production increased, radium availability was low. The Curies' process was still used for industrial radium extraction in 1940, but mixed bromides were then used for the fractionation. If the barium content of the uranium ore is not high enough it is easy to add some to carry the radium. These processes were applied to high grade uranium ores but may not work well with low grade ores. Small amounts of radium were still extracted from uranium ore by this method of mixed precipitation and ion exchange as late as the 1990s, and it is still in this range in 2015, while the annual production of pure radium compounds is only about 100 g in total as of 1984. The metal is isolated by reducing radium oxide with aluminium metal in a vacuum at 1,200 °C. which makes radium, the heaviest alkaline earth element, well suited for constraining new physics beyond the standard model. Some radium isotopes, such as radium 225, have octupole deformed parity doublets that enhance sensitivity to charge parity violating new physics by two to three orders of magnitude compared to 199Hg. Radium is also a promising candidate for trapped ion optical clocks. The radium ion has two subhertz linewidth transitions from the ground state that could serve as the clock transition in an optical clock. A 226Ra+ trapped ion atomic clock has been demonstrated on the to transition. Additionally, radium is particularly well suited for a transportable optical clock as all transitions necessary for clock operation can be addressed with direct diode lasers at common wavelengths. Some of the few practical uses of radium are derived from its radioactive properties. More recently discovered radioisotopes, such as cobalt 60 and caesium 137, 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. The isotope 223Ra (the chloride is under the trade name Xofigo) was approved by the United States Food and Drug Administration in 2013 for use in medicine as a cancer treatment of bone metastasis. The main indication of treatment with Xofigo is the therapy of bony metastases from castration resistant prostate cancer due to the favourable characteristics of this alpha emitter radiopharmaceutical. 225Ra has also been used in experiments concerning therapeutic irradiation, as it is the only reasonably long lived radium isotope which does not have radon as one of its daughters. Radium is still used in 2007 as a radiation source in some industrial radiography devices to check for flawed metallic parts, similarly to X ray imaging. as of 2004, radium beryllium neutron sources are still sometimes used,
but other materials such as polonium are more common: about 1,500 polonium beryllium neutron sources, with an individual activity of , have been used annually in Russia. These RaBeF4 based (α, n) neutron sources have been deprecated despite the high number of neutrons they emit (1.84×106 neutrons per second) in favour of 241Am–Be sources. Some of the biological effects of radium include the first case of "radium dermatitis", reported in 1900, two years after the element's discovery. The French physicist Antoine Becquerel carried a small ampoule of radium in his waistcoat pocket for six hours and reported that his skin became ulcerated. Pierre and Marie Curie were so intrigued by radiation that they sacrificed their own health to learn more about it. Pierre Curie attached a tube filled with radium to his arm for ten hours, which resulted in the appearance of a skin lesion, suggesting the use of radium to attack cancerous tissue as it had attacked healthy tissue. Handling of radium has been blamed for Marie Curie's death, due to aplastic anemia. A significant amount of radium's danger comes from its daughter radon: Being a gas, it can enter the body far more readily than can its parent radium. The world's largest concentration of 226Ra is stored within the Interim Waste Containment Structure, approximately 9.6 mile (15 km) north of Niagara Falls, New York. The Maximum Contaminant Level (MCL) for radium is 5pCi/L for drinking water, however, the OSHA does not set an exposure limit, as there is a radiation limit already set up.