キュリウム

キュリウム 化学特性,用途語,生産方法

• 解説

  キュリウム，Cm．原子番号96の元素．電子配置[Rn]5f 76d17s2の周期表3族アクチノイド元素．95番のAmより数か月先に，3番目に発見された超ウラン元素．キュリー夫妻にちなんで命名された．銀色の金属．密度13.5 g cm－3．融点1613.2 ℃．第一イオン化エネルギー587 kJ mol－1(6.09 eV)．通常の酸化数2～4．水溶液中で Cm3＋ は淡黄色．CmO，Cm2O3，CmO2，CmH2，CmCl3，CmF3が存在する．CmF3の磁化率がGdF3の磁化率と同じであることが1950年に見いだされ，ランタノイドとの類似性が確認された．現在，知られている同位体核種は，232～252の範囲に21種．質量数247の核種がもっとも長寿命で半減期1.56×107 y．半減期162.8 d でα崩壊する．242Cm は，グラム当たり3 W の熱量を発生するので，熱電素子としての利用が考えられる．

• 用途

  242Cm は，グラム当たり3 W の熱量を発生するので，熱電素子としての利用が考えられる．

• 製造

  1944年，原爆製造目的のマンハッタン・プロジェクトで，G.T. Seaborg(シーボーグ)らによってカリフォルニア大学バークレー校の60 inサイクロトロンで加速した 4He 原子核(a粒子)による 239Pu の衝撃で得られた．242Pu の逐次中性子吸収(原子炉中)後のβ崩壊生成物として 244Cm，252Cf のα崩壊生成物として 248Cm が得られ，前者は mg 単位(価格100ドル)の酸化物，後者は μg 単位で硝酸塩または塩化物の形で商業的に入手できる．

• 化学的特性

  silvery white, hard brittle metal; chemistry of trivalent state similar to that of trivalent lanthanides; α-emitter; hexagonal, a=0.3496nm, c=1.1331 nm; enthalpy of vaporization 1340 kJ/mol; ionic radius of Cm+++ is 0.0970nm; discovered in 1944; used in generating thermoelectric power for remote locations and in space; β-Cm is fcc, which is stable at <1340°C [HAW93] [MER06] [KIR78]

• 物理的性質

  After the discovery of plutonium and before elements 95 and 96 were discovered, theirexistence and properties were predicted. Additionally, chemical and physical properties werepredicted to be homologous (similar) to europium (₆₃Eu) and gadolinium (₆₄Gd), locatedin the rare-earth lanthanide series just above americium (₉₅Am) and curium (₉₆Cm) on theperiodic table. Once discovered, it was determined that curium is a silvery-white, heavymetal that is chemically more reactive than americium with properties similar to uraniumand plutonium. Its melting point is 1,345°C, its boiling point is ～1,300°C, and its density is13.51g/cm³.

• 同位体

  There are 23 isotopes of curium. All of them are man-made and radioactive.The most stable is curium-247, with a half-life of 1.56×10⁺⁷years (156,600,000 years),which through alpha decay transmutates into plutonium-243.

• 名前の由来

  Named after Pierre and Marie Curie.

• 天然物の起源

  There is no natural curium on Earth. All of its isotopes are man-made and artificiallyproduced through nuclear reactions with other elements. The curium isotope Cm-242 wasfirst produced by bombarding plutonium-239 with helium nuclei (alpha particles), whichcontributed neutrons that changed ₉₄Pu to ₉₆Cm.

• 特性

  Curium is a synthetic (not natural) transuranic element of the actinide series. It was determinedthat curium’s major valence and oxidation state was +3, similar to other elements of thisseries. The most stable isotope of curium is curium-247, with a half-life of 1.56×10⁺⁷years.

• 使用

  There are no major commercial uses for curium because of the extremely small amountproduced. In the future, the most important use of curium may be to provide the power forsmall, compact thermoelectric sources of electricity, by generating heat through the nucleardecay of radioisotope curium-241. These small, efficient power sources can be used in individualhomes or remote regions to provide electricity to areas that cannot secure it from othersources. It could also be used as a source of electricity in spacecraft. However, today curium’smain use is for basic scientific laboratory research.

• 定義

  A highly toxic radioactive silvery element of the actinoid series of metals. A transuranic element, it is not found naturally on Earth but is synthesized from plutonium. Curium-244 and curium-242 have been used in thermoelectric power generators.

• 危険性

  Curium metal and its compounds are radioactive bone-seeking poisons that attack theskeletal system of humans and animals. Care must be used in handling them.

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