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• 発見

  1952年太平洋で行われた熱核爆発実験の生成物からシーボーグらが発見，物理学者アインシュタインにちなんで命名。天然には存在せず，同位体はすべて人工的につくられる。1952年12月，カリフォルニア大学(バークレー校)のA. Ghiorsoらによって，同年11月のエニウェトク環礁での最初の水爆実験の残分中から，半減期20.5 d の253Esが確認された．逐次中性子吸収(原子炉中)で得られる．249Puから出発してオークリッジ国立研究所の高中性子束同位体製造用原子炉(HFIR)によって，数年間かかって3 mg のEsが製造された．1961年に，0.01 mg の253Esがメンデレビウム製造の原料として用いられた．融点1133 ℃ の金属．第一イオン化エネルギー629.0 kJ mol－1(6.52 eV)．酸化数2，3．水溶液中で Es3＋ と考えられている．現在，知られている同位体核種は240～258の範囲に19種．質量数252の核種がもっとも長寿命で半減期471 d．

• 解説

  周期表元素記号＝Es　原子番号＝99電子配置＝[Rn]5f106d17s2　おもな酸化数＝III超ウラン元素に属する人工元素の一つ。知られている同位体は質量数243から256までの14種で，そのうち半減期の最も長いものは254Es(276日)。1952年アメリカのギオーソAlbert Ghiorso，シーボーグGlenn Theodore Seaborgらが，太平洋で行われた熱核爆発実験で得られた破片から253Es(α崩壊，半減期20.47日)を見いだし(ウランの多段階の中性子捕獲と，いくつかのβ崩壊によって生成する)，99番元素であることを確かめた。
  株式会社平凡社 世界大百科事典 第２版について　情報

• 物理的性質

  Einsteinium belongs to group 13 (IIIA) of the heavy transuranic subseries of elementsfound in the actinide series. It was discovered after World War II, sometime in 1952, as atrace element in the residue from the massive explosion of the hydrogen bomb on Eniwetok Atoll in the Marshall Islands, located in the West Central Pacific Ocean. Although the atollwas obliterated, literally wiped off the face of the Earth, several heavy elements, both knownand unknown at that time, were detected in the aftermath of the explosion by a team of scientistsled by Albert Ghiorso of the Berkeley laboratory. Einsteinium was one of these traceelements that was detected. Its existence, as well as several other discovered elements, was notannounced until 1955, due to secrecy related to this new type of thermonuclear bomb. Themelting and boiling points as well as the density of einsteinium are not known because of theextremely small amounts that have been produced.

• 同位体

  There are total of 20 isotopes of einsteinium. Einsteinium is not found innature. All the isotopes are radioactive and are produced artificially. Their half-lives rangefrom eight seconds to 472 days. None have exceptionally long half-lives.

• 名前の由来

  Named after and in honor of the famous physical scientist Albert Einstein.

• 天然物の起源

  Einsteinium does not exist in nature and is not found in the Earth’s crust. It is produced insmall amounts by artificial nuclear transmutations of other radioactive elements rather than byadditional explosions of thermonuclear weapons. The formation of einsteinium from decay processesof other radioactive elements starts with plutonium and proceeds in five steps as follows:
  1. ²³⁹Pu →2 neutrons + gamma rays → ²⁴¹Pu → ²⁴¹Am + β-.
  2. ²⁴¹Am → 1 neutron + gamma → ²⁴²Am → ²⁴¹Cm + β-.
  3. ²⁴²Cm → 7 neutrons + gamma → ²⁴⁹Cm → ²⁴⁹Bk + β-.
  4. ²⁴⁹Bk → 1 neutron + gamma → ²⁵⁰Bk → ²⁵⁰Cf + β-.
  5. ²⁵⁰Cf → 3 neutrons + gamma → ²⁵³Cf → ²⁵³Es + β-.

• 特性

  Einsteinium’s most stable isotope, einsteinium-252, with a half-life of 472 days, decays intoberkelium-248 through alpha decay, and then into californium-252 through beta capture. Itcan also change into fermium-252 through beta decay.
  Einsteinium has homologous chemical and physical properties of the rare-earth holmium(₆₇Ho), located just above it in the lanthanide series in the periodic table.

• 来歴

  Einsteinium, the seventh transura- The Elements 4-11 nic element of the actinide series to be discovered, was identified by Ghiorso and co-workers at Berkeley in December 1952 in debris from the first large thermonuclear explosion, which took place in the Pacific in November 1952. The isotope produced was the 20-day ²⁵³Es isotope. In 1961, a sufficient amount of einsteinium was produced to permit separation of a macroscopic amount of ²⁵³Es. This sample weighed about 0.01 μg. A special magnetic-type balance was used in making this determination. ²⁵³Es so produced was used to produce mendelevium. About 3 μg of einsteinium has been produced at Oak Ridge National Laboratories by irradiating for several years kilogram quantities of ²³⁹Pu in a reactor to produce ²⁴²Pu. This was then fabricated into pellets of plutonium oxide and aluminum powder, and loaded into target rods for an initial 1- year irradiation at the Savannah River Plant, followed by irradiation in a HFIR (High Flux Isotopic Reactor). After 4 months in the HFIR the targets were removed for chemical separation of the einsteinium from californium. Nineteen isotopes and isomers of einsteinium are now recognized. 254Es has the longest half-life (276 days). Tracer studies using 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element. Einsteinium is extremely radioactive. Great care must be taken when handling it.

• 使用

  Einsteinium does not really have any common uses except as related to research in nuclearand chemical laboratories.

• 定義

  einsteinium: Symbol Es. A radioactivemetallic transuranic elementbelonging to the actinoids; a.n. 99;mass number of the most stable isotope254 (half-life 270 days). Elevenisotopes are known. The element wasfirst identified by A. Ghiorso and associatesin debris from the first hydrogenbomb explosion in 1952.Microgram quantities of the element did not become available until 1961.It is named after Albert Einstein.

• 危険性

  The radioisotopes of einsteinium are highly unstable and radioactive. The small amount ofthe element and its compounds produced are not likely to be available in most laboratories.Thus, they do not pose any general hazard except in the case of scientists working with nuclearmaterials who must take precautions in handling exotic elements.

• 工業用途

  Element 99, called einsteinium, was originallynamed ekaholmium because it appears tohave chemical properties similar to holmium. Itis produced by bombarding uranium-238 withstripped nitrogen atoms. It decays rapidly toform the lighter berkelium, or element 97. Neptunium(element 93), californium (element 98),and illinium (element 61), are also made atomically.The latter also has the names florentiumand promethium.

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