ラジウム

ラジウム 化学特性,用途語,生産方法

• 解説

  ラジウム，原子番号88の元素．電子配置[Rn]7s2の周期表2族アルカリ土類金属元素に属する天然放射性元素．安定同位体のない元素のため，原子量が与えられていない．質量数201～234の同位体が知られている．1898年P. and M. Curie(キュリー)夫妻により発見された．元素名はラテン語のradius(光線)からキュリー夫妻によって命名された．天然には4種の核種が存在するが，ウラン崩壊系列に属する 226Ra の半減期がもっとも長く1.600×103 y で，4.871 MeV のα粒子を放出して 222Rn となる．14C を放出して 212Pb となる崩壊形式(分岐率3×10－9 ％)も報告されている．
  

• 性質

  ラジウム，銀白色の金属．空気中で酸化されて表面は黒化する．密度5.0 g cm－3(25 ℃)．融点700 ℃，沸点1140 ℃．第一イオン化エネルギー5.279 eV．通常の化合物中の酸化数2．水，酸に溶けて水素を発生する．アルカリ土類金属中もっとも化学的に活性である．硫酸ラジウムはきわめて水に難溶．

• 用途

  ウラン精製の副産物として製造されるが，通常，塩化物または臭化物として取り扱われている．人工放射性同位元素がつくられるようになるまでは，γ線源，α線源として用いられた．夜光時計の塗料として，硫化亜鉛との混合物が用いられていたが，放射線障害のため現在は使用されていない．かつての放射能の単位1キュリーはRa 1 g の放射能をもとに崩壊数3.70×1010/s と定められていたが，現在は毎秒崩壊数そのものが単位(ベクレル，Bq)となっている。

• 化学的特性

  Radium (Ra) is a radioactive element, found naturally occurring in the environment. Ra is a silvery- white-metallic solid @ 25℃; it tarnishes black when exposed to air. It is an alkaline earth metal; there are 33 isotopes, all of them are unstable. Radium is commonly available as radium bromide (RaBr2 ) or radium chloride (RaCl2 ).

• 物理的性質

  Radium is the last element in group 2 and is very similar to the other alkali earth metals,which makes it the largest and heaviest element in the group. It particularly resembles barium,which is just above it in group 2 of the periodic table. Radium is a bright white radioactiveluminescent alkali earth metal that turns black when exposed to air. Its melting point is700°C, its boiling point is 1,140°C, and its density is approximately 5.0 g/cm³.

• 同位体

  There are no stable isotopes of radium. Radium has 25 known radioisotopes,ranging from Ra-206 to Ra-230. Their half-lives range from a fraction of a second tohundreds of years. Radium-226 was discovered by the Curies and has a half-life ofabout 1630 years. Ra-226 is the most abundant isotope, and thus, Ra-226 is used todetermine radium’s atomic mass.Various radium isotopes are derived through a series of radioactive decay processes. Forexample, Ra-223 is derived from the decay of actinium. Ra-228 and Ra-224 are the resultof the series of thorium decays, and Ra-226 is a result of the decay of the uranium series.

• 名前の由来

  Radium’s name is derived from the Latin word radius, which means “ray.

• 天然物の起源

  Radium is the 85th most abundant element found in the Earth’s crust. Radium is found inthe uranium ores pitchblende and chalcolite, which are both very radioactive. Radium metalexists to the extent of only one part to every three million parts of the uranium ore (pitchblende). Only about one gram of radium is found in every seven or eight tons of uraniumore. This scarcity seems to be the reason that only about five pounds of uranium are producedeach year in the entire world. Uranium ores are found in the states of Utah, New Mexico, andColorado in the United States and in Canada, the Czech Republic, Slovakia, Russia, Zaire,and France.

• 特性

  Radium is extremely radioactive. It glows in the dark with a faint bluish light. Radium’sradioisotopes undergo a series of four decay processes; each decay process ends with a stableisotope of lead. Radium-223 decays to Pb-207; radium-224 and radium-228decay to Pb-208;radium-226 decays to Pb-206; and radium-225 decays to Pb-209. During the decay processesthree types of radiation—alpha (α), beta (β), and gamma (γ)—are emitted.In addition to being radioactive, radium is extremely chemically reactive and forms manycompounds. These radium compounds are not only radioactive but also toxic and should behandled by experienced personnel.

• 使用

  Radium’s most important use is as a source of radiation in industry, medicine, and laboratories. The isotope radium-226, which is the most abundant of all the 25 isotopes and has ahalf-life of 1630 years, is the only useful form of the element. It is used in the medical treatment of malignant cancer growth. It kills cancer cells that have spread throughout the body.Other uses are to produce phosphorescence and fluorescence in organic compounds andfor scintillation screens on instruments used to detect radiation. Radium salts were used in thepast to paint the dials of luminous clock faces that glow in the dark.

• 定義

  A white radioactive luminescent metallic element of the alkaline- earth group. It has several short-lived radioisotopes and one long-lived isotope, radium-226 (half-life 1602 years). Radium is found in uranium ores, such as the oxides pitchblende and carnotite. It was formerly used in luminous paints and radiotherapy. Symbol: Ra; m.p. 700°C; b.p. 1140°C; r.d. 5 (approx. 20°C); p.n. 88; r.a.m. 226.0254 (²²⁶Ra).

• 危険性

  Because radium energetically emits three types of radiation, it poses great danger to anyone handling it. In addition, it is toxic. If it is ingested in even small amounts, it replaces bone tissue, which can result in radiation sickness and death.
  One of the decay products of radium is the gas radon, which can seep up through the Earth s crust into basements and slab level homes. Good ventilation assures that the radon does not accumulate to the extent that would be harmful.
  At one time, women painted clock and watch dials with luminous radium paint that was a mixture of radium salts and zinc sulfide. They would place the small brushes between their lips and tongue to make the bristles more pointed, in order to paint fine lines with the radium paint. Over the years, they developed cancers that resulted in badly eaten-away and disfigured lips and jaws. Once the danger was known, luminous radium paint was banned for this use. Today, promethium (Pm-147), with a half-life of 2.4 years, is used for this purpose.

• 発がん性

  The U.S. EPA has classified radium as a class A carcinogen, meaning that there are sufficient data to support a link between exposure to radium and the development of human cancer. The α-particle radiation associated with radium is recognized as the causative agent for sarcomas of the bone and carcinomas of the paranasal sinuses in humans. A study attempting to ascertain the dose–incidence relationship for induction of these tumors examined 1474 women employed in the U.S. radium dial painting industry before 1930. This population exhibited 61 known cases of bone sarcoma and 21 cases of carcinoma of the paranasal sinuses or the mastoid air cells. Of these individuals, the radium body burden was known for 759, among whom there were 38 cases of bone sarcoma and 17 head carcinomas.

• 環境運命予測

  Radium is released to the environment from a variety of sources, including milling and mining operations focused on phosphates and uranium, waste streams from factories used to produce products containing radium, or waste byproducts from production, such as phosphate fertilizers. The most important route of radium release into the environment is the combustion of coal, and released radium is estimated at 150 Ci per year (or 5.55×10¹² Bq). Radium released into the atmosphere will remain in particulate form until wet or dry deposition. Radium adsorbs to soils, and is not expected to volatize from soils or water due to its ionic nature. In water, radium exists as Ra⁺² and can interact with sediments and dissolve in water, and therefore generally adsorbs to sediments at the emission site and is not transported. Some isotopes of radium are very short lived, but radium-226 has a half-life of 1600 years, making long-range transport more likely, though generally only through an atmospheric route. Radium’s ionic nature makes bioaccumulation or biomagnification unlikely.

• 輸送方法

  UN3323(does not appear in the 49CFR hazard materials tables ) Radioactive material, Type C package, nonfissile or fissile excepted. UN2915 Radioactive mate- rial, Type A package nonspecial form, nonfissile or fissile- excepted, Hazard class: 7-Radioactive material; Labels: None. A1 and A2 values for Radium- 226 taken from y173.435 (see also Table A-1 in 10CFR71(Appendix A): A1 (SpecialForm * ) 0.3 TBq (8.11Ci); A2 (NormalForm) 0.02TBq (0.541Ci))

• 不和合性

  Metallic radium is highly chemically reactive. It forms compounds that are very similar to barium compounds, making separation of the two elements difficult. On contact with water, radium forms flammable hydrogen gas.

• 廃棄物の処理

  Radioactive material consid- ered waste and must be retained in containers for disposi- tion by the authorizing institution. Drain disposal is prohibited. It is the responsibility of the operating institu- tion to arrange for the proper disposal of all forms of any radioisotopes. The use, storage, transportation, labeling, and disposal of radioactive material are regulated through the Nuclear Regulatory Commission (NRC) using 10 CFR (Code of Federal Regulations) as the regulatory basis and 49 CFR (Transportation).

ラジウム 生産企業

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7440-14-4, ラジウム キーワード