📚 Uses of Radioactive Isotopes | 放射性同位素的应用
Radioactive isotopes, or radioisotopes, are atoms with unstable nuclei that emit ionising radiation as they decay. Although this radiation can be hazardous, scientists and engineers have found many safe and valuable ways to harness the properties of radioisotopes. From diagnosing disease in hospitals to controlling the thickness of paper in factories, radioisotopes play a vital role in modern life. Understanding how the type of radiation, half‑life, and chemical behaviour of an isotope determine its best application is a key part of IGCSE Edexcel Science.
放射性同位素是原子核不稳定、会放出电离辐射的原子。虽然这种辐射具有危险性，但科学家和工程师已经找到许多安全而有价值的方法来利用放射性同位素的特性。从医院里的疾病诊断到工厂中纸张厚度的控制，放射性同位素在现代生活中扮演着至关重要的角色。理解同位素的辐射类型、半衰期以及化学行为如何决定其最佳用途，是IGCSE Edexcel科学的重要内容。
1. What Are Radioactive Isotopes? | 什么是放射性同位素？
A radioactive isotope is a variant of a chemical element that has an unstable nucleus. The instability arises from an imbalance between the number of protons and neutrons. To become more stable, the nucleus emits ionising radiation in the form of alpha particles (helium nuclei, ⁴₂He), beta particles (high‑energy electrons, ⁰₋₁e or positrons), or gamma rays (high‑frequency electromagnetic waves). Many radioisotopes occur naturally, such as uranium‑238 and carbon‑14, while others are produced artificially in nuclear reactors or particle accelerators, including technetium‑99m and iodine‑131.
放射性同位素是一种化学元素的变体，其原子核不稳定。不稳定来源于质子数与中子数之间的不平衡。为了变得更稳定，原子核以α粒子（氦核，⁴₂He）、β粒子（高能电子，⁰₋₁e 或正电子）或γ射线（高频电磁波）的形式放出电离辐射。许多放射性同位素天然存在，例如铀‑238和碳‑14，而其他一些则是在核反应堆或粒子加速器中人工制造的，包括锝‑99m和碘‑131。
2. Key Properties for Practical Use | 实际应用的关键特性
When selecting a radioisotope for a specific job, three properties are critical: the type of radiation emitted, the half‑life of the isotope, and its chemical properties. Firstly, alpha particles are highly ionising but have very low penetrating power – they can be stopped by a sheet of paper or skin – so alpha emitters are used where localised ionisation is needed, such as in smoke detectors. Beta particles penetrate a few millimetres of aluminium, making beta emitters ideal for thickness gauging in industry. Gamma rays can pass through several centimetres of lead and are therefore ideal for medical imaging and radiotherapy.
在为一个特定的工作选择放射性同位素时，有三个关键特性：发射的辐射类型、同位素的半衰期以及它的化学性质。首先，α粒子电离能力很强，但穿透力非常低——一张纸或皮肤就能挡住它们——因此α发射体用于需要局部电离的场合，比如烟雾探测器。β粒子能穿透几毫米的铝，因此β发射体非常适用于工业测厚。γ射线可以穿透几厘米厚的铅，所以是医学成像和放射治疗的理想选择。
Second, the half‑life – the time taken for half of the radioactive nuclei in a sample to decay – must suit the application. A tracer used inside the body must have a half‑life long enough to allow imaging but short enough to minimise radiation dose; technetium‑99m (half‑life 6 hours) is a perfect example. For dating ancient materials, an isotope such as carbon‑14 (half‑life 5730 years) is needed. Finally, the chemical properties of the isotope determine whether it can be incorporated into molecules of biological or industrial interest, such as iodine‑131 being taken up by the thyroid gland.
其次，半衰期——样本中一半的放射性原子核发生衰变所需的时间——必须与应用相匹配。用于体内的示踪剂必须有足够长的半衰期以便成像，但又必须足够短以尽量降低辐射剂量；锝‑99m（半衰期6小时）就是一个完美的例子。对于古代材料的年代测定，则需要使用像碳‑14（半衰期5730年）这样的同位素。最后，同位素的化学性质决定它能否结合到具有生物或工业意义的分子中，例如碘‑131能够被甲状腺摄取。
3. Medical Diagnostics: Tracers | 医学诊断：示踪剂
One of the most common uses of radioisotopes is as tracers in medicine. A radioactive tracer is a small amount of a radioisotope attached to a biologically active molecule. When introduced into the body, the tracer emits gamma rays that can be detected outside the body by a gamma camera, allowing doctors to create an image of an organ or to study a physiological process. The ideal tracer emits gamma rays (which can escape the body), has a short half‑life, and is non‑toxic. Technetium‑99m, which emits pure gamma rays and has a half‑life of 6 hours, is attached to various compounds to image the skeleton, heart, lungs, kidneys, and brain. The patient receives a very low radiation dose, comparable to that from a few X‑rays.
放射性同位素最常见的用途之一是作为医学示踪剂。放射性示踪剂是将少量放射性同位素附着在生物活性分子上。当示踪剂被引入体内后，它发射的γ射线可以被体外的γ照相机探测到，使医生能够生成器官的图像或研究某一生理过程。理想的示踪剂发射γ射线（可穿出体外），半衰期短，并且无毒性。锝‑99m发射纯γ射线，半衰期为6小时，可与多种化合物结合，用于骨骼、心脏、肺、肾和脑的成像。患者接受的辐射剂量非常低，相当于几次X射线检查的剂量。
A classic example is the use of iodine‑131 (half‑life 8 days) as a tracer to assess thyroid function. The thyroid gland naturally absorbs iodine from the bloodstream; if a patient swallows a small dose of iodine‑131, the activity can be measured to see how well the thyroid is working. Because ¹³¹I emits both beta particles and gamma rays, it can be used as a diagnostic tracer in very small amounts, although in larger doses it becomes a therapeutic agent.
一个典型的例子是使用碘‑131（半衰期8天）作为示踪剂来评估甲状腺功能。甲状腺会自然地从血流中吸收碘；如果患者吞服小剂量的碘‑131，就可以测量其活度来观察甲状腺的工作状况。因为¹³¹I既发射β粒子又发射γ射线，所以极小的剂量可用作诊断示踪剂，尽管在较大剂量下它就成了治疗药物。
4. Radiotherapy: Treating Cancer | 放射治疗：癌症治疗
Radioisotopes are also used to destroy cancerous cells. In teletherapy, a high‑activity gamma source, often cobalt‑60 (half‑life 5.27 years), is placed in a machine that directs a carefully collimated beam of gamma rays at a tumour from outside the body. The gamma rays kill cancer cells and shrink tumours, but because healthy tissue is unavoidably exposed, the beam is rotated around the patient to concentrate the dose on the tumour while sparing surrounding tissue. Cobalt‑60 emits gamma rays with energies of about 1.17 MeV and 1.33 MeV, which are sufficiently penetrating to reach deep‑seated tumours.
放射性同位素也用于摧毁癌细胞。在远距离放射治疗中，通常使用高活度γ源，如钴‑60（半衰期5.27年），将它置于一台机器中，从体外将一束经过精确准直的γ射线对准肿瘤。γ射线杀死癌细胞，使肿瘤缩小，但由于健康组织不可避免地会受到照射，射线束会围绕患者旋转，以将剂量集中在肿瘤上，同时保护周围组织。钴‑60发射能量约为1.17 MeV和1.33 MeV的γ射线，穿透力足够到达深部肿瘤。
Brachytherapy is an alternative technique in which a sealed radioactive source is placed directly inside or next to the tumour. Small seeds or wires containing iodine‑125 (half‑life 60 days) or iridium‑192 (half‑life 74 days) are often used. The short range of the emitted radiation limits damage to surrounding healthy tissue. In the treatment of thyroid cancer, patients may be given iodine‑131 orally; the beta particles emitted within the thyroid destroy overactive or cancerous tissue while causing little irradiation of the rest of the body.
近距离放射治疗是另一种技术，将密封的放射源直接放入肿瘤内部或紧邻肿瘤。常使用含碘‑125（半衰期60天）或铱‑192（半衰期74天）的小颗粒或线。所发射辐射的射程短，可以限制对周围健康组织的损害。在治疗甲状腺癌时，患者可能口服碘‑131；在甲状腺内发射的β粒子摧毁过度活跃或癌变的组织，而对身体其他部位的照射则很少。
5. Sterilisation of Medical Equipment | 医疗设备消毒
Gamma radiation from cobalt‑60 or caesium‑137 is widely used to sterilise disposable medical equipment such as syringes, surgical gloves, and catheters. The process, known as radiation sterilisation, exposes packaged products to a high dose of gamma rays that destroy the DNA of bacteria, viruses, and fungi, rendering them inactive. Because gamma rays penetrate deeply through packaging, items can be sterilised after they are sealed, guaranteeing sterility until the package is opened. The technique does not use heat or chemicals, so it is suitable for heat‑sensitive materials like plastics. Strict safety standards ensure that the products do not become radioactive; the irradiated objects simply receive a dose of radiation, just as a patient receives an X‑ray without becoming a radiation source.
来自钴‑60或铯‑137的γ射线被广泛用于对一次性医疗设备（如注射器、外科手套和导管）进行消毒。这一过程称为辐射灭菌，即将包装好的产品暴露于高剂量的γ射线下，破坏细菌、病毒和真菌的DNA，使其失去活性。由于γ射线能深度穿透包装，物品可在密封后进行灭菌，从而保证在打开包装之前一直保持无菌状态。该技术不使用高温或化学品，因此非常适合塑料等热敏感材料。严格的安全标准确保产品不会变得具有放射性；被照射的物体只是接收了辐射剂量，就像患者接受X射线检查后不会变成辐射源一样。
6. Industrial Gauging: Thickness Control | 工业测量：厚度控制
In the manufacturing of materials such as paper, plastic film, and metal foil, controlling uniform thickness is critical for quality and cost control. A radioisotope thickness gauge consists of a beta source (e.g. strontium‑90 or krypton‑85) on one side of the moving sheet and a radiation detector on the other. The number of beta particles that pass through the sheet is measured; as thickness increases, fewer particles are detected. The detector signal is fed into a feedback loop that automatically adjusts rollers to maintain the desired thickness – all without touching the product. Beta emitters are chosen because alpha particles would be completely absorbed by even the thinnest sheet, and gamma rays would pass through too easily for fine control.
在纸张、塑料薄膜和金属箔等材料的生产中，控制均匀的厚度对质量和成本控制至关重要。放射性同位素厚度计由一个β源（如锶‑90或氪‑85）置于移动片材的一侧，另一侧放置一个辐射探测器。测量穿过片材的β粒子数量；随着厚度增加，探测到的粒子数减少。探测器信号被输入反馈回路，自动调整压辊以保持所需厚度——整个过程无需接触产品。选择β发射体是因为α粒子连最薄的片材也能被完全吸收，而γ射线太容易穿透，不利于精细控制。
A similar principle is used in density gauges for liquids or slurries flowing through a pipe: a gamma source and detector placed on opposite sides of the pipe measure attenuation that depends on the density of the contents.
类似原理也用于管道中液体或泥浆的密度计：一个γ源和探测器放在管道的对面，测量衰减程度，衰减取决于内容物的密度。
7. Smoke Detectors | 烟雾探测器
Many household smoke detectors contain a tiny amount of americium‑241, an alpha‑emitting radioisotope with a half‑life of 432 years. Inside the detector, the alpha particles ionise air molecules in an ionisation chamber, creating a small but constant electric current between two electrodes. When smoke particles enter the chamber, they attach to the ions, reducing the current. The drop in current triggers the alarm. Americium‑241 is ideal because alpha radiation has a very short range in air (a few centimetres) and is completely contained within the detector housing, posing no risk to occupants under normal use. The long half‑life ensures the detector functions reliably for decades.
许多家用烟雾探测器含有极少量的镅‑241，一种半衰期为432年的α发射性同位素。在探测器内部，α粒子电离电离室中的空气分子，在两个电极之间产生一个微弱但恒定的电流。当烟雾粒子进入电离室时，它们附着在离子上，使电流减小。电流的下降触发报警器。镅‑241之所以理想，是因为α辐射在空气中的射程很短（几厘米），并且完全被探测器外壳所屏蔽，在正常情况下对住户没有风险。较长的半衰期确保探测器能可靠工作数十年。
8. Carbon‑14 Dating | 碳‑14测年
Carbon‑14 dating is a powerful method for determining the age of ancient organic materials, such as wood, bone, cloth, and seeds. Cosmic rays continuously produce carbon‑14 (half‑life 5730 years) in the upper atmosphere; living organisms maintain a constant carbon‑14 to carbon‑12 ratio through respiration and feeding. When an organism dies, it stops exchanging carbon with the environment, and the carbon‑14 inside it begins to decay at a known rate. By measuring the remaining ¹⁴C activity of a sample and comparing it with the original atmospheric level, archaeologists can calculate how long ago the organism died. The technique can date objects up to about 50 000 years old.
碳‑14测年是确定古代有机材料（如木材、骨骼、布和种子）年代的一种强大方法。宇宙射线在大气高层不断产生碳‑14（半衰期5730年）；活着的生物体通过呼吸和进食保持恒定的碳‑14与碳‑12的比例。当生物体死亡后，它停止与环境交换碳，体内的碳‑14开始以已知的速率衰变。通过测量样本中剩余的¹⁴C活度，并将其与原始大气水平相比较，考古学家可以计算出该生物体死亡的时间。该技术可测定距今大约5万年以内的物体。
9. Leak Detection in Pipelines | 管道泄漏检测
Radioisotopes can be used as tracers to locate leaks in underground pipelines or to study the flow of fluids. A small amount of a gamma‑emitting isotope, such as sodium‑24 (half‑life 15 hours) or iodine‑131, is injected into the pipeline. If a leak exists, the radioactive material seeps out and concentrates in the surrounding soil. A portable radiation detector is then moved along the surface above the pipeline; a spike in readings pinpoints the leak location. Gamma emitters are used because the radiation must penetrate through the pipe walls and soil to be detected. The short half‑life ensures that the radioactivity decays to negligible levels quickly after the test, avoiding long‑term environmental contamination.
放射性同位素可用作示踪剂来定位地下管道的泄漏或研究流体流动。将少量γ发射性同位素，如钠‑24（半衰期15小时）或碘‑131，注入管道。如果存在泄漏，放射性物质将渗出并集中在周围的土壤中。然后将一个便携式辐射探测器沿管道上方的地面移动；读数突然升高的位置就指示出泄漏点。使用γ发射体是因为辐射必须穿透管壁和土壤才能被检测到。短半衰期确保试验结束后放射性迅速衰减至可忽略的水平，避免长期的环境污染。
10. Tracers in Agriculture and Biology | 农业与生物学中的示踪剂
Radioactive tracers help scientists understand how plants take up nutrients and how fertilisers work. For example, a plant can be watered with a solution containing phosphorus‑32 (beta emitter, half‑life 14.3 days), a radioisotope of an essential nutrient. Samples of the plant’s leaves and roots are periodically tested for radioactivity; the distribution of ³²P reveals how efficiently the plant absorbs and transports phosphorus. This allows the development of more effective fertilisers. Similarly, carbon‑14 is used to trace the pathway of carbon in photosynthesis and in the food chain. In these applications, the use of radioisotopes must be carefully controlled to protect the environment and avoid contaminating food supplies.
放射性示踪剂帮助科学家了解植物如何吸收养分以及肥料如何发挥作用。例如，可以用含有磷‑32（β发射体，半衰期14.3天）的溶液浇灌植物，磷‑32是必需养分的一种放射性同位素。定期检测植物叶片和根部的放射性；³²P的分布揭示出植物吸收和运输磷的效率。这有助于开发更有效的肥料。同样，碳‑14可用于追踪光合作用及食物链中碳的路径。在这些应用中，必须严格控制放射性同位素的使用，以保护环境并避免污染食物供应。
11. Safety Considerations | 安全注意事项
All uses of radioisotopes are accompanied by rigorous safety protocols. Ionising radiation can damage DNA and increase the risk of cancer, so exposure must be kept as low as reasonably achievable (the ALARA principle). Workers handling radioisotopes wear protective clothing and use shielding appropriate to the radiation type: thick lead for gamma rays, Perspex for beta particles, and minimal shielding for alpha particles because they are easily stopped. Radioactive materials are stored in lead‑lined containers and handled with remote manipulators when necessary. Time of exposure is kept short, and distance from the source is maximised – radiation intensity decreases according to the inverse square law. In medical settings, the benefit to the patient is always weighed against the risk, and the lowest effective dose is used.
所有放射性同位素的使用都伴随着严格的安全规程。电离辐射会损害DNA并增加患癌风险，因此暴露必须保持在合理可行的最低水平（ALARA原则）。处理放射性同位素的工作人员穿戴防护服，并根据辐射类型使用适当的屏蔽：γ射线用厚铅，β粒子用有机玻璃，α粒子因其容易被阻挡只需极少的屏蔽。放射性物质储存在内衬铅的容器中，必要时用远程操纵器操作。暴露时间尽量缩短，与源的距离尽量增大——辐射强度按平方反比定律衰减。在医疗环境中，始终权衡对患者的益处与风险，并使用最低有效剂量。
Waste disposal is another crucial aspect. Radioactive waste is categorised by its activity level and half‑life. Short‑lived waste may be stored until it decays to a safe level, while long‑lived waste must be encased in glass and buried in deep geological repositories. Strict national and international regulations govern all stages from production to disposal.
废物处置是另一个关键方面。放射性废物按其活度水平和半衰期分类。短寿命废物可以贮存起来直到衰变至安全水平，而长寿命废物则必须用玻璃固化并深埋于地质处置库。从生产到处置的所有阶段都有严格的国家和国际法规管理。
12. Summary: Choosing the Right Isotope | 总结：选择合适的同位素
The remarkable usefulness of radioisotopes across medicine, industry, and research relies on matching the isotope’s radiation type, half‑life, and chemical behaviour to the task. Gamma‑emitting technetium‑99m allows safe internal imaging; beta‑emitting strontium‑90 controls paper thickness without contact; alpha‑emitting americium‑241 protects homes from fire; and long‑lived carbon‑14 uncovers the past. Understanding these principles not only prepares students for IGCSE Edexcel Science but also reveals how physics and chemistry work together to solve real‑world problems safely and effectively.
放射性同位素在医学、工业和研究领域的非凡用途，依赖于将同位素的辐射类型、半衰期和化学行为与任务相匹配。发射γ射线的锝‑99m可实现安全的体内成像；发射β粒子的锶‑90可无接触地控制纸张厚度；发射α粒子的镅‑241可保护家庭免受火灾；长寿命的碳‑14可揭示过去。理解这些原理不仅为IGCSE Edexcel科学考试做好准备，还展示了物理和化学如何协同工作，安全有效地解决现实世界中的问题。
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