actinium

actinium 化学特性,用途語,生産方法

• 解説

  Ac．原子番号89の元素．電子配置[Rn]6d17s2の周期表3族アクチノイド元素．ギリシア語の“光線”を意味するακτινοσから名づけられた．1899年，A. Debierne，1902年，F. Gieselによりウラン鉱石中から独立に発見された．現在，知られている同位体核種は，206～236の範囲に核異性体を含めて35種．質量数227の核種がもっとも長寿命で半減期21.77 y．主としてβ崩壊して227Thになる．天然には，この核種が235Uからはじまるアクチニウム系列の中間に存在する．トリウム系列中にも半減期6.15 h のβ崩壊核種228Acが存在する．単体は，フッ化物AcF3を1100 ℃ 以上の高温でLi蒸気で還元すると得られる．銀白色の金属．密度10.07 g mL－1．融点1050 ℃，沸点3200 ℃．第一イオン化エネルギー498.7 kJ mol－1(5.17 eV)．化学的性質は希土類元素，とくにランタンに似るが，より塩基性である．酸化数3．[CAS 7440-34-8]
  森北出版「化学辞典（第2版）

• 物理的性質

  Actinium is an extremely radioactive, silvery-white, heavy metal that glows in the dark withan eerie bluish light. It decays rapidly which makes it difficult to study, given that it changesinto thorium and francium through electron capture and alpha decay. Its melting point is1,051°C, its boiling point is 3,198°C, and its density is 10.07g/cm³.

• 同位体

  There are a total of 35 isotopes of actinium, none of which are stable. All areradioactive, and none exist in the Earth’s crust in any large amounts, although a few canbe extracted from large quantities of pitchblende and other minerals. All are extremelyscarce. Those produced artificially in nuclear reactors, cyclotrons, or linear acceleratorshave relatively short half-lives, ranging from 69 nanoseconds to 21 years.

• 名前の由来

  The name “actinium” is derived from the Greek word(s) aktis or aktinos, meaning “beam” or “ray.”

• 天然物の起源

  Actinium is a rare element that is found in very small amounts in uranium ore (pitchblende),making it difficult and expensive to extract even a small quantity. It is less expensiveand easier to produce small amounts by bombarding the element radium with neutrons in anuclear reactor. Actinium has few commercial uses.

• 特性

  Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic tableand the first of the actinide series of metallic elements that share similar chemical and physicalcharacteristics. Actinium is also closely related in its characteristics to the element lanthanum,which is located just above it in group 3. The elements in this series range from atomic number89 (actinium) through 103 (lawrencium). Actinium’s most stable isotope is actinium-227,with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 throughbeta decay, and both of these isotopes are decay products from uranium-235.

• 来歴

  Its presence in air was suspected by Cavendish in 1785, discovered by Lord Rayleigh and Sir William Ramsay in 1894. The gas is prepared by fractionation of liquid air, the atmosphere containing 0.94% argon. The atmosphere of Mars contains 1.6% of 40Ar and 5 p.p.m. of 36Ar. Argon is two and one half times as soluble in water as nitrogen, having about the same solubility as oxygen. It is recognized by the characteristic lines in the red end of the spectrum. It is used in electric light bulbs and in fluorescent tubes at a pressure of about 400 Pa, and in filling photo tubes, glow tubes, etc. Argon is also used as an inert gas shield for arc welding and cutting, as a blanket for the production of titanium and other reactive elements, and as a protective atmosphere for growing silicon and germanium crystals. Argon is colorless and odorless, both as a gas and liquid. It is available in high-purity form. Commercial argon is available at a cost of about 3￠ per cubic foot. Argon is considered to be a very inert gas and is not known to form true chemical compounds, as do krypton, xenon, and radon. However, it does form a hydrate having a dissociation pressure of 105 atm at 0°C. Ion molecules such as (ArKr)+, (ArXe)+, (NeAr)+ have been observed spectroscopically. Argon also forms a clathrate with β-hydroquinone. This clathrate is stable and can be stored for a considerable time, but a true chemical bond does not exist. Van der Waals’ forces act to hold the argon. In August 2000, researchers at the University of Helsinki, Finland reported they made a new argon compound HArF 4-4 The Elements by shining UV light on frozen argon that contained a small amount of HF. Naturally occurring argon is a mixture of three isotopes. Seventeen other radioactive isotopes are now known to exist. Commercial argon is priced at about $70/300 cu. ft. or 8.5 cu. meters.

• 使用

  There are no significant uses for actinium because of its scarcity and the expense of producingit. The only practical use for small amounts of actinium is as a tracer in medicine andindustry. It is too difficult to produce in substantial quantities to make it useful. Actiniumcan be used as a source of neutrons to bombard other elements to produce isotopes of thoseelements, but other neutron sources are less expensive.

• 定義

  actinium: Symbol Ac. A silveryradioactive metallic element belongingto group 3 (formerly IIIA) of theperiodic table; a.n. 89; mass numberof most stable isotope 227 (half-life21.7 years); m.p. 1050 ± 50°C; b.p.3200°C (estimated). Actinium–227 occursin natural uranium to an extentof about 0.715%. Actinium-228 (halflife6.13 hours) also occurs in nature.There are 22 other artificial isotopes,all radioactive and all with very shorthalf-lives. Its chemistry is similar tothat of lanthanum. Its main use is asa source of alpha particles. The elementwas discovered by A. Debiernein 1899.

• 危険性

  Most of the radioactive isotopes of actinium pose an extreme radiation hazard. They arebone-seeking radioactive poisons.

, actinium キーワード