radon

Japanese: ラドン

Rn. Atomic number 86. Electron configuration [Xe] ^{4f145d106s26p6} ^. No stable isotopes, so no atomic weight is given. Isotopes with mass numbers from 195 ^{to 228} ^are known. All are radioactive. ^222Rn is the most stable, with a half-life of 3.8235 days. ^222Rn was first discovered as a radioactive gas produced from radium (P. and M. Curie in 1899). In 1900, E. Rutherford discovered the radioactive gas ( ^220Rn ) produced from thorium and called it emanation. In the same year, F. Dorn confirmed their discoveries, and named the gas produced from radium emanation and that from thorium emanation. Subsequently, FO Giesel and A. Debierne discovered ²¹⁹ Rn (actinium emanation) from actinium in a similar manner. ²²² Rn is commonly called emanation or radium emanation, ²²⁰ Rn is called thoron, and ²¹⁹ Rn is called actinon. Radon is formed between the three naturally occurring decay series (uranium, thorium, and actinium), so it is present in small amounts along with these elements.
Various names were proposed, but IUPAC selected radon in 1923. It is the heaviest gaseous element. Its melting point is -71 °C, and its boiling point is -61.8 °C. Its density is 9.73 g L ^-1 (gas, 0 °C), 4.4 g cm ^-3 (liquid, -62 °C). The gas and liquid are colorless and odorless. The solid emits yellow to orange phosphorescence (at liquid air temperature). It is soluble in water and easily soluble in organic solvents. Until recently, it was thought to be chemically inert (see alternative terms: noble gas compounds), but it is known to react with F ₂ or ClF ₃ to produce RnF ₂ and RnF ₄ and other fluorides such as RnF ₆ at 250 °C in the presence of NiF ₂ using BrF ₅ as a solvent, and is considered to be the most reactive of the noble gases.
It is used as a medical radiation source. In recent years, the accumulation of radon inside buildings from surrounding soil, rocks, concrete, and other building materials has been raised as a possible cause of internal exposure through inhalation. According to a survey commissioned by the former Science and Technology Agency, the average indoor radon concentration in Japan is estimated to be 15.5 Bq cm ^-3 , which is a fraction to a few thousandths lower than the values in other countries, and is therefore considered to pose little risk. The average indoor radon concentration in the United States is 48 Bq cm ^-3 , and it is considered to be the second leading cause of lung cancer after tobacco. According to the Enforcement Order of the Law Concerning the Prevention of Radiation Hazards Due to Radioisotopes, etc., "Determining the Quantity of Isotopes, etc." (revised in 2005), the concentration limit for ²²² Rn in the air is 3 x 10 ^-5 Bq/cm ³ . [CAS 10043-92-2]

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

Japanese:

Rn．原子番号86の元素．電子配置[Xe]4f¹⁴5d¹⁰6s²6p⁶の周期表18族希(貴)ガス元素．安定同位体のない元素のため，原子量が与えられていない．質量数195～228までの同位体が知られている．すべて放射性．²²²Rn がもっとも安定で半減期3.8235 d．²²²Rn がラジウムから発生する放射性気体として一番最初に発見された(1899年，P. and M. Curie(キュリー)夫妻)．1900年にE. Rutherford(ラザフォード)がトリウムから発生する放射性気体(²²⁰Rn)を発見しemanationとよんだ．同年，F. Dornが両者の発見を確認し，ラジウムから発生する気体をradium emanation，トリウムからのものをthorium emanationとした．引き続きF.O. GieselとA. Debierneが同様にアクチニウムから ²¹⁹Rn(actinium emanation)を発見した．慣用名として ²²²Rn をエマネーションまたはラジウムエマネーション，²²⁰Rn をトロン，²¹⁹Rn をアクチノンとよぶこともある．ラドンは天然に存在する三つの崩壊系列(ウラン，トリウム，アクチニウム)の中間に生成するので，これらの元素に伴って微量存在する．
さまざまな名称が提案されたが，IUPACは1923年にラドンを選択した．もっとも重い気体元素．融点－71 ℃，沸点－61.8 ℃．密度9.73 g L^－1(気体，0 ℃)，4.4 g cm^－3(液体，－62 ℃)．気体と液体は無色，無臭．固体は黄色から橙色(液体空気温度)のりん光を放つ．水に可溶，有機溶媒に易溶．近年まで化学的に不活性と思われていたが([別用語参照]希ガス化合物)，F₂ またはClF₃との反応でRnF₂，BrF₅を溶媒としてNiF₂の存在下250 ℃ でRnF₄，RnF₆などフッ化物をつくることが知られており，希ガス中でもっとも反応性に富むと考えられている．
医療用放射線源として用いられる．近年周辺の土壌・岩石あるいはコンクリートなど，建築材料からの建物内のラドンの蓄積が，吸入による内部被ばくの可能性として取り上げられている．旧科学技術庁委託の調査によると，わが国の屋内ラドン濃度平均値は15.5 Bq cm^－3 と推定されており，諸外国の数値の数分の一から数千分の一と低いことから，危険性は少ないと判断されている．アメリカの屋内ラドン濃度平均値は48 Bq cm^－3 で，タバコにつぐ第二位の肺がん発がん原因とされる．放射性同位元素等による放射線障害防止に関する法律施行令「同位元素の数量等を定める件」(平成17年改正)によると，²²²Rn の空気中の濃度限界3×10^－5 Bq/cm³．[CAS 10043-92-2]