Radium is a crucial intermediate element in the 铀-238衰变链 (4n+2 series). It is produced by the alpha decay of thorium-230 (ionium) and itself decays into radon-222 by alpha emission. Several radium isotopes exist in different chains, but the most important is 镭-226 (half-life 1600 years), which is in secular equilibrium with uranium-238 in ancient minerals. Its presence and relative abundance are therefore directly related to the uranium content of the environment.
The 铀-钍/镭 isotopic system is used to date geological processes on timescales ranging from a few years to about 500,000 years. The \(^{226}\mathrm{Ra}/^{230}\mathrm{Th}\) ratio is particularly useful for dating 海洋碳酸盐 (corals, concretions) and recent oceanic sediments. Since radium is more soluble than thorium, it is leached from continents and transported to the oceans. Measuring its activity in sediment cores allows the reconstruction of sedimentation rates and past climate changes.
Radium has four natural isotopes with different half-lives (\(^{223}\mathrm{Ra}\), 11.4 days; \(^{224}\mathrm{Ra}\), 3.66 days; \(^{226}\mathrm{Ra}\), 1600 years; \(^{228}\mathrm{Ra}\), 5.75 years). This "string" of isotopes with decreasing timescales makes it an 适用于不同尺度过程的理想示踪剂:
Radium-226 present in soils and rocks is the 氡-222的直接来源, a radioactive gas that migrates into buildings. The radium content of a soil is therefore the main determinant of the radon potential of a region.
The name "镭" was chosen by its discoverers, 皮埃尔和玛丽·居里, and derives from the Latin word "半径", meaning "ray". This name celebrates the most striking property of the new element: its intense 放射性, which manifests itself by the emission of invisible but detectable "rays". The Curies had already named "polonium"; "radium" completed the pair of radioactive elements they had extracted from pitchblende (a uranium ore).
In 1898, following the work of 亨利·贝克勒尔 (1852-1903) on uranium, 玛丽·居里 (1867-1934) discovered that 沥青铀矿 (a uranium ore) was much more radioactive than pure uranium. She deduced, with her husband Pierre, the presence of unknown, more radioactive elements. After months of titanic and physically grueling work in a rudimentary shed, they managed to separate two new elements: first polonium (July 1898), then 镭 (December 1898). They announced it to the Academy of Sciences on December 26, 1898. The definitive proof and isolation of radium in the form of pure chloride (RaCl₂) would not come until 1902, after the treatment of several tons of ore.
Pure metallic radium was first isolated in 1910 by 玛丽·居里 in collaboration with 安德烈-路易·德比埃纳 (1874-1949), by electrolysis of molten radium chloride on a mercury cathode, followed by distillation of the mercury. This success consolidated Marie Curie's international fame, who received a 第二个诺贝尔奖 (this time in Chemistry) in 1911, becoming the first person to win two Nobels in different disciplines.
The extraordinary properties of radium—its intense radioactivity, spontaneous luminescence (due to the excitation of air or impurities), and decay heat—made it a true 科学和商业界的知名人士. It was attributed almost miraculous virtues, leading to a craze:
这一时期展现了人们对新技术的迷恋与其危险性认知之间的鸿沟。
Radium does not exist in its native state. It is present in minute quantities (about 1 part per 10¹¹) in 铀 ores, mainly pitchblende (UO₂) and carnotite (K₂(UO₂)₂(VO₄)₂·3H₂O). Historically, the richest mines were in 约阿希姆斯塔尔 (now the Czech Republic) and the 比属刚果. Extraction was extremely difficult and costly: hundreds of tons of ore had to be processed to obtain one gram of radium, making it the most expensive substance in the world (up to $120,000 per gram in the 1910s, equivalent to several million today).
如今，镭已不再被有意生产。医学上使用的少量镭来自历史库存，或作为核废料处理的副产品产生。其需求几乎已消失。
Radium (symbol Ra, atomic number 88) is an element of group 2, the 碱土金属. It is the heaviest and most radioactive member of this family, which includes beryllium, magnesium, calcium, strontium, and barium. Its atom has 88 protons and, depending on the isotope, 135 to 150 neutrons. The most stable isotope, \(^{226}\mathrm{Ra}\), has 138 neutrons. Its electronic configuration is [Rn] 7s², with two valence electrons in the 7s shell.
镭是一种银白色的碱土金属，在空气中会因氧化和氮化作用迅速变黑。其性质主要从钡的性质推断而来，但因强烈的放射性而变得复杂。
在固态形式下，它以体心立方结构结晶。
Estimated melting point: ~973 K (~700 °C).
Estimated boiling point: ~2010 K (~1737 °C).
Chemically, radium closely resembles 钡, but is even more reactive. It is a highly electropositive metal.
由于镭的放射性及其衰变产物会污染溶液，其化学性质难以研究。
Atomic number: 88.
Group: 2 (Alkaline earth metals).
Electronic configuration: [Rn] 7s².
Oxidation state: +2 (exclusive).
Most stable isotope: \(^{226}\mathrm{Ra}\) (T½ = 1600 years).
Appearance: Silvery-white metal that blackens in air.
| 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/应用 |
|---|---|---|---|---|---|---|
| 镭-223 — \(^{223}\mathrm{Ra}\) | 88 | 135 | 223.018502 u | 铀-235（4n+3） | 11.43天（α） | Used in medicine under the trade name Xofigo® for the treatment of painful bone metastases from prostate cancer (targeted alpha therapy). |
| 镭-224 — \(^{224}\mathrm{Ra}\) | 88 | 136 | 224.020212 u | 钍-232（4n） | 3.66天（α） | 历史上用于医学。如今被研究用于α疗法。 |
| 镭-226 — \(^{226}\mathrm{Ra}\) | 88 | 138 | 226.025410 u | 铀-238（4n+2） | 1600年（α） | 历史上最重要且最具历史意义的同位素. Discovered by the Curies. Used for decades in curietherapy and luminous paints. Source of radon-222. |
| 镭-228 — \(^{228}\mathrm{Ra}\) | 88 | 140 | 228.031070 u | 钍-232（4n） | 5.75年（β⁻） | 中钍 I。历史上曾单独用于发光涂料。钍-228的衰变产物。 |
注意：:
Electron shells: 电子如何在原子核周围组织.
镭有88个电子，分布在七个电子壳层上。其电子构型[Rn] 7s²很简单：由氡（一种稀有气体）的构型加上7s壳层中的两个额外电子组成。这也可以写成：K(2) L(8) M(18) N(32) O(18) P(8) Q(2)，或完整形式：1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 7s²。
K壳层 (n=1): 2 electrons (1s²).
L壳层（n=2）: 8 electrons (2s² 2p⁶).
M壳层 (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).
Q壳层 (n=7): 2 electrons (7s²).
Radium has two 价电子 (7s²). Like other alkaline earth metals, it easily loses these two electrons to form the Ra²⁺ ion, thus achieving the stable configuration of the noble gas radon. This high electropositivity explains its great reactivity with water and acids.
In the 1910s-20s, the U.S. Radium Corporation employed hundreds of young women to hand-paint watch dials with radium paint. To obtain a fine point, the workers were encouraged to 用嘴唇润湿笔尖 ("lip-pointing"), thus ingesting small amounts of radium daily. In addition, they worked in dusty workshops and sometimes smeared their hair and nails with fluorescent paint for fun.
As early as the 1920s, the workers began to develop horrible pathologies: 严重贫血、颌骨坏死（"镭颌病"） (the jawbones literally disintegrated), 自发性骨折、骨肉瘤及多种癌症. Doctors were initially perplexed, but the link with radium was established by Dr. 哈里森·马特兰 (1883-1954). Once ingested, radium behaved like calcium and became fixed in the bones, irradiating the bone marrow and surrounding tissues from within for decades.
Five workers, the "镭姑娘" (including Grace Fryer, Katherine Schaub), filed a landmark lawsuit against their employer in 1927. Despite the company's delaying tactics and the deteriorating health of the plaintiffs, they won their case in 1928. This trial:
The toxicity of radium is purely 放射学的 (unlike lead or mercury, which have chemical toxicity). Once incorporated (mainly by ingestion, rarely by inhalation of dust), the Ra²⁺ ion follows the metabolism of calcium:
对镭工人、接受镭治疗的患者以及钟表匠进行的长期流行病学研究，为内照射α辐射效应提供了基础数据。
如今，镭的处理采取了极其严格的防护措施：
Former industrial uses of radium have left a legacy of 污染场地 (former luminous paint factories, watchmaking workshops, waste dumps). The long half-life of Ra-226 (1600 years) means that this contamination will persist for millennia.
收藏家和博物馆必须意识到这一风险。物品应存放在通风的展示柜中，处理时需戴手套，未经专业人员指导切勿打开或修复。剥落的油漆尤其危险。
镭作为神奇材料的时代已经结束。它的未来存在于两个截然不同的领域：
镭将作为开启放射性时代的元素载入史册，它承载着科学天才、天真的热情以及最终导致严格监管和对放射风险高度警觉的人类苦难。
原子的各种形态：从古代直觉到量子力学 
