promethium

Pm. Atomic number 61. Electron configuration [Xe] ^4f56s2 . Lanthanide element in group ³ of the periodic table. One of the rare earth elements of the cerium group. Isotopes with mass numbers between 126 and 163 are known. All are radioactive. There are no stable isotopes. It does not exist on Earth, but its presence has been observed in the spectroscopy of stars in the Andromeda Galaxy. The longest-lived isotope (half-life 17.7 years) has a mass number of 145. In 1941, it was reported that it was produced by irradiating neodymium and praseodymium with deuterons at the cyclotron at Ohio State University, and it was named cyclonium, but it was not confirmed. It was not confirmed until 1945, when JA Marinsky, LE Glendenin, and CD Coryell separated it from the fission products of a graphite reactor at Oak Ridge National Laboratory using ion exchange resin. It was classified as a military secret, so it was not announced until 1947. Being an artificial element, it was named after Prometheus in Greek mythology, who is said to have stolen fire from heaven. Density 7.22 g cm ^-3 . Melting point 1042 °C, boiling point 2700 °C. First ionization energy 5.582 eV. Atomic radius 183 pm. Its main oxidation state is 3, and its chemical properties are similar to those of neodymium and samarium. Over 30 compounds have been made. Promethium salts fluoresce pale blue or green in the dark due to their high radioactivity. The most common use is to improve the discharge starting characteristics of fluorescent light starters, using the β ^- decay nuclide ¹⁴⁷ Pm, which has a half-life of 2.62 y. [CAS 7440-12-2]

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

Pm．原子番号61の元素．電子配置[Xe]4f ⁵6s²の周期表3族ランタノイド元素．希土類元素セリウム族の一つ．質量数126～163までの同位体核種が知られている．すべて放射性核種．安定同位体は存在しない．地上には存在しないが，アンドロメダ星雲中の星に分光スペクトルから存在が観測された．もっとも長寿命(半減期17.7 y)の同位体の質量数は145．1941年，オハイオ州立大学のサイクロトンでネオジム，プラセオジムを重陽子で照射して生成したと報告し，サイクロニウムと命名したが確認されず，J.A. Marinsky，L.E. Glendenin，C.D. Coryellがオークリッジ国立研究所の黒鉛炉の核分裂生成物からイオン交換樹脂で分離してはじめて1945年に確認された．軍事機密とされていたので発表は1947年．人工元素であることから天上から火を盗んだとされるギリシア神話のプロメテウスにちなんで命名された．密度7.22 g cm^－3．融点1042 ℃，沸点2700 ℃．第一イオン化エネルギー5.582 eV．原子半径183 pm．主要酸化数3で化学的性質はネオジム，サマリウムに似ている．30種類あまりの化合物がつくられた．プロメチウム塩は高い放射能のために暗闇で淡青または緑色蛍光を発する．もっとも普及している用途は，蛍光灯点灯管の放電開始特性向上用で，半減期2.62 y の β^－ 崩壊核種 ¹⁴⁷Pm が用いられている．[CAS 7440-12-2]

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