Radon is a gaseous element continuously produced in the Earth's crust by the 镭的放射性衰变, itself derived from the uranium-238, uranium-235, and thorium-232 chains. It is the only naturally radioactive noble gas under normal conditions. Three natural isotopes are significant, each corresponding to these chains:
Radon-222 formed in radium-containing minerals can, depending on soil porosity and water content, 扩散到表面 and be released into the atmosphere. This flux, called 氡析出, varies significantly depending on geology (granitic and uranium-rich shales > sedimentary rocks), season, atmospheric pressure, and humidity. Measuring this flux is used in geophysics for:
Once in the atmosphere, radon-222 (an inert gas) is transported by winds. Since it decays with a known half-life, its decrease with distance from its continental source (oceans produce very little) allows the study of 气团混合时间 between continents and oceans. In oceans, dissolved radon (produced by radium in sediments) serves as a tracer for vertical mixing processes and air-sea exchanges.
The name "radon" is derived from 镭, its direct parent in the decay chain. The isotope \(^{222}\mathrm{Rn}\) was initially called "镭辐射" or simply "散发" (denoted Em) by its discoverers, as it "emanated" from radium. Later, when isotopes from thorium and actinium were discovered, they were named 钍射气（Tn） and 锕射气（An）, respectively. The generic name "radon" (symbol Rn) for element 86 was officially adopted in 1923.
Radon-222 was discovered in 1900 by the German physicist 弗里德里希·恩斯特·多恩. While studying radium compounds newly discovered by the Curies, he noticed that radium emitted a radioactive gas. He demonstrated that this gas, which he called "radium emanation," was itself radioactive and transformed into other solid elements. This discovery was crucial for understanding radioactive decay series.
In 1908, the Scottish chemist 威廉·拉姆齐爵士 (already discoverer of the noble gases argon, krypton, xenon, and neon) and his assistant 罗伯特·惠特洛-格雷 succeeded in isolating radon, measuring its density, and proving it was the 已知稀有气体中最重的. They managed to condense enough to observe its emission spectrum, confirming its status as an element. Ramsay received the Nobel Prize in Chemistry in 1904 for his work on inert gases, even before the discovery of radon.
As early as the 1920s, radon was suspected of causing the high incidence of lung cancer among uranium miners (notably in the Joachimsthal mines in Czechoslovakia and later in New Mexico). However, it was not until the 1980年代 that epidemiological studies (such as those on American miners) firmly established the link between radon exposure and lung cancer. In the 1990s, awareness spread to 国内风险, transforming radon from a scientific curiosity into a major public health issue.
氡气无处不在，但其浓度差异很大。
氡本身并非“生产”而来；它由自然衰变持续产生，需在其积聚处加以管理。
Radon (symbol Rn, atomic number 86) is an element of group 18, the 稀有气体 (or rare gases). It is the heaviest and only naturally radioactive member of this group under normal conditions (oganesson, Z=118, is synthetic). Its atom has 86 protons and, depending on the isotope, 131 to 150 neutrons. The isotope \(^{222}\mathrm{Rn}\) has 136 neutrons. Its electronic configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶, with a complete p valence shell (6 electrons), making it a chemically inert gas.
氡是一种无色、无味、无臭的稀有气体。
在固态形式下，氡因其放射性而呈现黄橙色。
Radon melts at 202 K（-71 °C） and boils at 211 K（-61.7 °C）. It can be liquefied relatively easily by cooling.
As a noble gas, radon is extremely inert. However, due to its large size and high polarizability, it is the 最活泼的稀有气体. Theoretical calculations predict it could form a few unstable compounds, such as 氟化氡（RnF₂） and possibly oxides or clathrate complexes. In practice, only solid-state compounds, highly unstable and radioactive, have been obtained in minute quantities (clathrates with water or hydrocarbons). Its chemistry has little practical application.
State (20°C, 1 atm): Colorless gas.
Density (gas, 0°C): 9.73 g/L (8.1 x air).
Melting point: 202 K (-71 °C).
Boiling point: 211 K (-61.7 °C).
Electronic configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶.
Radioactivity: Main isotope \(^{222}\mathrm{Rn}\), α, T½=3.82 days.
| 同位素 / 符号 | 质子（Z） | 中子（N） | 原子质量（u） | 母链 | 半衰期 / 衰变模式 | 备注/重要性 |
|---|---|---|---|---|---|---|
| 氡-222 — \(^{222}\mathrm{Rn}\) | 86 | 136 | 222.017578 u | 铀-238（4n+2） | 3.8235天（α） | 最重要的同位素. Half-life long enough to migrate from soil and accumulate in buildings. Mainly responsible for domestic health risk. |
| 氡-220 — \(^{220}\mathrm{Rn}\)（钍射气） | 86 | 134 | 220.011394 u | 钍-232（4n） | 55.6秒（α） | 半衰期极短，限制了其在远离源头处的积累。主要对处理富钍材料（独居石砂、陶瓷）的行业构成危险。 |
| 氡-219 — \(^{219}\mathrm{Rn}\)（锕射气） | 86 | 133 | 219.009480 u | 铀-235（4n+3） | 3.96秒（α） | 因其超短半衰期及U-235丰度极低（0.72%），对公众健康的影响可忽略不计。 |
注意：:
Electron shells: 电子如何围绕原子核组织.
氡的86个电子分布在六个电子壳层上。其电子排布为[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶，价电子层（6p）完全填满，因此具有极高的化学稳定性和稀有气体特性。该排布也可写作：K(2) L(8) M(18) N(32) O(18) P(8)，或完整形式：1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶。
K壳层 (n=1): 2 electrons (1s²).
L壳层（n=2）: 8 electrons (2s² 2p⁶).
M层（n=3）: 18 electrons (3s² 3p⁶ 3d¹⁰).
N壳层（n=4）: 32 electrons (4s² 4p⁶ 4d¹⁰ 4f¹⁴).
O壳层（n=5）: 18 electrons (5s² 5p⁶ 5d¹⁰).
P壳层 (n=6): 8 electrons (6s² 6p⁶).
Radon has 8 价电子 in its outer shell (6s² 6p⁶), achieving the stable 字节 configuration. This saturated electronic structure makes it extremely reluctant to form classical covalent bonds. Its first ionization potential is relatively low for a noble gas (10.75 eV), but still too high for easy chemistry. Any attempt to form compounds (such as RnF₂) requires very strong oxidants like fluorine, and the resulting compounds are thermodynamically unstable and decompose rapidly.
This inertia is crucial for its 环境行为: once formed in the soil, radon does not react with minerals or water; it diffuses freely as an atomic gas. In the lungs, it does not chemically interact with tissues; its danger is purely radiological.
The radon gas itself, once inhaled, is largely exhaled. The danger comes from its 固体和放射性衰变产物:
这些颗粒（通常带电）会附着于环境气溶胶或灰尘上。一旦被吸入，它们会沉积在呼吸道中，尤其是支气管内。其在肺组织中的α和β衰变会直接辐射上皮细胞，造成DNA损伤，从而可能引发癌症。
The International Agency for Research on Cancer (IARC) classifies radon as a 某些人类致癌物. It is the 肺癌的第二大原因 after smoking, and the 非吸烟者中的主要原因. It is estimated that about 3 to 14% of lung cancers worldwide are attributable to radon, corresponding to tens of thousands of deaths annually. The risk is multiplicative with smoking: a smoker exposed to radon has a much higher risk of lung cancer than the sum of individual risks.
卫生部门设定了建议采取纠正措施的阈值：
室外平均浓度通常为5至15 Bq/m³。在室内，受影响最严重的区域浓度范围可从低于10 Bq/m³到超过10,000 Bq/m³不等。
目标是降低氡浓度。按效果和成本排序的技术包括：
Many countries have established 氡潜势图 based on geology and measurements. In France, the IRSN has published a municipal map classifying communes into 3 potential categories. These maps are used to prioritize information actions and monitoring obligations (schools, workplaces in high-potential areas).
氡气问题是一个完全可以识别和管理的环境健康问题。当前的挑战是：
氡，一种看不见的天然气体，完美地说明了地质现象如何直接对人群健康产生影响，以及科学和法规如何结合以减轻这种风险。
原子的各种形态：从古代直觉到量子力学 
