polonium

Po. An element with atomic number 84. It is a chalcogen element in group 16 of the periodic table with the electron configuration [Xe]4f ¹⁴ 5d ¹⁰ 6s ² 6p ^4. There is no atomic weight because it has no stable isotopes and does not naturally exhibit a specific isotopic composition. It was discovered in uraninite in 1898 by M. Curie as the first radioactive nuclide (mass number 210). The element was named after Curie's country of birth, Poland.
Isotopes with mass numbers ranging from 188 to 220 are known. ²⁰⁹ Po is the longest-lived alpha-decay nuclide with a half-life of 102 y. ²¹⁰ Po is an alpha-decay nuclide with a half-life of 138.376 d. It has an alpha-ray energy of 5.3 MeV. It exists in the uranium series (classical name RaF) and decays to lead (RaG) with a mass number of 206. It is used as a standard source of alpha rays, an ion source, and in space radioactive batteries, taking advantage of its high calorific value of 140 W g ^-1. As an alpha emitter, it is very harmful, and organs and blood cells are particularly susceptible to damage from polonium. It is a silvery metal at room temperature. It has stronger metallic properties than its relative, tellurium. In the past, it was extracted from uranium ore, but nowadays, ²¹⁰ Po is extracted from the β ^- decay of ²¹⁰ Bi obtained in the ²⁰⁹ Bi(n,γ) ²¹⁰ Bi(RaE) nuclear reaction in nuclear reactors. In addition to ²¹⁰ Po, six other radioisotopes exist in nature (in the decay series): ²¹⁸ Po(RaA), ²¹⁴ Po(RaC′), ²¹⁶ Po(ThA), ²¹² Po(ThC′), ²¹⁵ Po(AcA), and ²¹¹ Po(AcC′). Silver-white metal. It exists in two phases, α and β, and the cubic α phase transforms to the trigonal β phase at 36 °C. Density 9.32 g cm ^-3 (20 °C, α phase). Melting point 254 °C, boiling point 962 °C. First ionization energy 8.42 eV. Standard electrode potential Po ²⁺ /Po 0.368 V. Oxidation states -2, 2, 4, 6. It gradually forms an oxide film in air. It reacts with chlorine, bromine, and iodine at 200-400 °C to produce PoX ₄ (X = halogen). It is insoluble in water, but soluble in hydrochloric acid, sulfuric acid, and concentrated nitric acid. Metallic Po precipitates on iron and nickel from a nitric acid solution.
²¹⁰ Po Oxides, hydroxides and nitrates: Air concentration limit 9× ^10-6 Bq/ ^cm3 , wastewater or drainage concentration limit 6× ^10-4 Bq/ ^cm3 . [CAS 7440-08-6]

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Po．原子番号84の元素．電子配置[Xe]4f ¹⁴5d¹⁰6s²6p⁴の周期表16族カルコゲン元素．安定同位体がなく，天然で特定の同位体組成を示さないので原子量はない．1898年にM. Curie(キュリー)により，せんウラン鉱中に最初の放射性核種(質量数210)として発見された．元素名はCurieの生国ポーランドにちなんで命名された．
質量数188～220までの同位体核種が知られる．²⁰⁹Po がもっとも長寿命で半減期102 y のα崩壊核種．²¹⁰Po は半減期138.376 d のα崩壊核種．α線エネルギー5.3 MeV．ウラン系列中に存在(古典名RaF)し，崩壊により質量数206の鉛(RaG)となる．α線の標準線源，イオン源，高い発生熱量140 W g^－1 を利用して宇宙用放射能電池に使用される．α放射体であるので非常に有害で，臓器，血球などはとくにポロニウムの害を受けやすい．常温で銀色の金属．同族のテルルより金属性が強い．昔はウラン鉱より抽出したが，現在は原子炉で²⁰⁹Bi(n，γ)²¹⁰Bi(RaE)核反応で得られる ²¹⁰Bi の β^－ 崩壊により生じる ²¹⁰Po を抽出する．²¹⁰Po のほか6種の放射性同位体，²¹⁸Po(RaA)，²¹⁴Po(RaC′)，²¹⁶Po(ThA)，²¹²Po(ThC′)，²¹⁵Po(AcA)，²¹¹Po(AcC′)が天然に存在(崩壊系列中)する．銀白色の金属．α，βの二相があり，立方晶のα相は36 ℃ で三方晶系のβ相に転移する．密度9.32 g cm^－3(20 ℃，α相)．融点254 ℃，沸点962 ℃．第一イオン化エネルギー8.42 eV．標準電極電位 Po^2＋/Po 0.368 V．酸化数－2，2，4，6．空気中で徐々に酸化皮膜をつくる．塩素，臭素，ヨウ素とは，200～400 ℃ で反応してPoX₄(X ＝ ハロゲン)を生じる．水に不溶，塩酸，硫酸，濃硝酸に可溶．硝酸溶液から鉄やニッケル上に金属Poが析出する．
²¹⁰Po 酸化物，水酸化物及び硝酸塩の空気中濃度限度9×10^－6 Bq/cm³，廃液中または排水中濃度限度6×10^－4 Bq/cm³．[CAS 7440-08-6]

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