Astatine 化学特性,用途語,生産方法
解説
アスタチン，At．原子番号85の元素．電子配置[Xe]4f 145d106s26p5の周期表17族人工放射性ハロゲン元素．ギリシア語の“不安定”を意味するαστατοσから名づけられた．1940年，カリフォルニア大学でD.R. Corson，K.R. MacKenzie，E. SegréによってBiをα粒子で衝撃して得られた．現在，知られている同位体核種は，194～223の範囲に核異性体を含めて41種．質量数210の核種がもっとも長寿命で半減期8.1 h．211Atは7.2 h，209Atは5.4 h．209Atと210Atは主として β＋ 崩壊，211Atは β＋ 崩壊とα崩壊がほぼ同じ割合で起こる．天然にも，ごく微量の218Atがウラン系列，215At，219Atがアクチニウム系列，216Atがトリウム系列の分岐中間崩壊生成核種として存在する．Biのα粒子衝撃後，ターゲットから昇華法で比較的長寿命の209,210,211Atが得られるが，化学実験用のトレーサーとしてしか用途はない．融点302 ℃，沸点337 ℃ のハロゲン．一般的性質はヨウ素に似るが，ヨウ素より金属性である．ヨウ素と同様，人体に入ると甲状腺に集中する．ハロゲン間化合物AtCl，AtBr，AtIが合成された．酸化数－1，1，3，5，7．水に微溶，ベンゼン，四塩化炭素，二硫化炭素に可溶．
化学的特性
radioactive crystal(s) halogen with 20 isotopes; heaviest of the halogens; 209At, t1/2=5.5 h; 210At, t1/2=8.3 h; more metallic than iodine; preparation: from Bi by α-particle bombardment; possible medical uses, concentrates in thyroid gland [HAW93] [MER06]
物理的性質
Physical properties of this element have not been well investigated due to short half-lives of isotopes. The element is volatile; may be distilled in vacuum at room temperature in a glass apparatus; and condensed in a dry ice trap. It is soluble in chloroform, ether, hexane and many other organic solvents. Solubility in water should be of low order.
天然物の起源
Astatine is one of the rarest elements in nature. Extremely small amounts of short-lived isotopes At-215, At-217, At-218 and At-219 are naturally found occurring in equilibrium with uranium, neptunium and thorium isotopes. The element was named by Corson, MacKenzie and Segre who produced the first of its isotope At-211 in 1940 by bombarding bismuth with alpha particles. Since then many isotopes in the mass range 200 to 219 have been synthesized. All isotopes, however, are unstable, their half-lives ranging between a few microseconds to less than ten hours. The most stable ones are At-210, At-211 and At-209. No use of this element is known so far.
危険性
Exposure to radiation may cause cancer. Studies on experimental animals show it induces tumors.
Astatine 上流と下流の製品情報
原材料
準備製品