📚 Applications of Radioactivity | 放射性的应用
Radioactivity, although often associated with danger, has become an indispensable tool in modern society. From diagnosing illnesses and treating cancer to powering cities and uncovering the age of ancient artefacts, ionising radiation plays a vital role in science, medicine, industry and energy production. Understanding how different types of radiation interact with matter allows us to exploit their properties safely and effectively, while careful management of risks ensures these benefits outweigh the hazards.
放射性虽然常与危险联系在一起，但已成为现代社会中不可或缺的工具。从诊断疾病、治疗癌症到为城市供电、揭示古代文物的年代，电离辐射在科学、医学、工业和能源生产中发挥着至关重要的作用。理解不同类型的辐射如何与物质相互作用，使我们能够安全有效地利用它们的特性，而审慎的风险管理确保了这些好处远大于危害。
1. Radioactive Decay and Half-Life | 放射性衰变与半衰期
All applications of radioactivity rely on the predictable behaviour of unstable atomic nuclei. Radioactive decay is a random, spontaneous process in which an unstable nucleus emits alpha (α), beta (β) or gamma (γ) radiation to become more stable. The half-life of a radioisotope is the time taken for half of the nuclei in a sample to decay, and this property determines how long a source remains significantly active. For example, technetium‑99m (Tc‑99m) has a half‑life of about 6 hours, making it ideal for medical tracing because it decays quickly enough to minimise the patient's radiation dose, yet lasts long enough for imaging.
放射性的所有应用都依赖于不稳定原子核的可预测行为。放射性衰变是一种随机、自发的过程，不稳定的原子核通过释放阿尔法（α）、贝塔（β）或伽马（γ）辐射而变得更加稳定。放射性同位素的半衰期是指样品中一半的原子核发生衰变所需的时间，这一性质决定了辐射源能保持显著活性的时长。例如，锝‑99m（Tc‑99m）的半衰期约为 6 小时，这使它成为医学示踪的理想选择，因为它衰变得足够快，可以尽量降低患者的辐射剂量，同时又能持续足够长的时间用于成像。
2. Medical Tracers: Seeing Inside the Body | 医用示踪剂：洞察人体内部
A radioactive tracer is a small amount of a gamma‑emitting isotope introduced into the body to diagnose illnesses. Gamma rays are used because they are penetrating enough to be detected outside the body. The tracer accumulates in specific organs, and a gamma camera records the radiation to produce an image of organ function. Tc‑99m is the most common tracer; it is injected into the bloodstream and monitored as it passes through the heart, revealing blockages. Iodine‑131 (with a longer half‑life) is used to check thyroid gland activity because the thyroid naturally absorbs iodine. The patient receives a low activity dose, and the short effective half‑life of the tracer means most of it decays or is excreted within a day.
放射性示踪剂是引入人体内以诊断疾病的一小部分发射伽马射线的同位素。使用伽马射线是因为它具有足够的穿透力，可以在体外被探测到。示踪剂会在特定器官中聚集，伽马相机记录辐射后生成反映器官功能的影像。Tc‑99m 是最常用的示踪剂；它被注入血液，并随着流经心脏的过程被监测，从而揭示血管堵塞。碘‑131（半衰期较长）用于检查甲状腺活动，因为甲状腺会自然吸收碘。患者接受的活度剂量很低，而且示踪剂的有效半衰期很短，大部分会在一天内衰变或排出体外。
3. Radiotherapy: Destroying Cancerous Cells | 放射治疗：摧毁癌细胞
Radiotherapy uses high‑energy ionising radiation to kill cancer cells or shrink tumours. Gamma rays from cobalt‑60 (Co‑60) sources are focused on a tumour from multiple angles, delivering a lethal dose to the cancer while sparing surrounding healthy tissue as much as possible. Alternatively, a linear accelerator produces a beam of high‑energy X‑rays or electrons. Beta‑emitting sources, such as small pellets of yttrium‑90, can be implanted directly into a tumour (brachytherapy) to deliver a concentrated dose locally. Because ionising radiation can also damage healthy cells, treatment is planned with millimetre precision, and fractionated doses are given over several weeks to allow normal cells to repair between sessions.
放射治疗使用高能电离辐射杀死癌细胞或使肿瘤缩小。来自钴‑60（Co‑60）源的伽马射线从多个角度聚焦在肿瘤上，向癌组织输送致死剂量，同时尽可能保护周围健康组织。另一种方式是由直线加速器产生高能 X 射线或电子束。发射贝塔粒子的源，例如钇‑90 小颗粒，可以直接植入肿瘤内部（近距离放射治疗），在局部给予集中剂量。由于电离辐射也可能损伤健康细胞，治疗计划的精度达到毫米级，并在数周内分次给药，以便正常细胞在两次照射之间修复。
4. Sterilisation of Medical Equipment | 医疗设备消毒
Gamma radiation from sources like cobalt‑60 is widely used to sterilise disposable medical supplies such as syringes, bandages and surgical gloves. These items are packed in sealed boxes and passed through a strong gamma field; the ionising radiation destroys bacteria, viruses and other pathogens by breaking their DNA, without the need for high temperatures or chemicals that could leave residues. This method is cold and penetrating, so the equipment remains sterile inside its packaging until opened. A high dose of about 25 kGy is typically used, but the source itself does not make the irradiated items radioactive.
来自钴‑60 等源的伽马辐射被广泛用于对一次性医疗用品进行消毒，如注射器、绷带和手术手套。这些物品装在密封箱中，通过强伽马场；电离辐射通过破坏细菌和病毒的 DNA 来杀灭病原体，无需高温或可能留下残留物的化学药剂。这种方法属于冷消毒且具有穿透性，因此设备在包装内可一直保持无菌状态，直至开封。通常会使用约 25 千戈瑞的高剂量，但辐射源本身不会使被辐照物品带上放射性。
5. Thickness Monitoring in Industry | 工业测厚
In manufacturing, beta and gamma sources are used for automatic thickness control of materials such as paper, plastic film and sheet metal. A radioactive source is placed on one side of the material and a detector on the other. If the material becomes too thick, fewer beta particles or gamma photons reach the detector, and the signal triggers rollers to adjust the pressure. Beta emitters like krypton‑85 are suitable for thin materials, while gamma sources are needed for thicker products. This non‑contact method operates continuously and accurately, improving quality without damaging the surface.
在制造业中，贝塔源和伽马源被用于纸张、塑料薄膜和金属板材等材料的自动厚度控制。将放射源置于材料的一侧，探测器置于另一侧。如果材料过厚，到达探测器的贝塔粒子或伽马光子就会减少，信号将触发滚轮调整压力。氪‑85 等贝塔发射体适用于薄材料，而较厚的产品则需要伽马源。这种非接触式方法可以持续、精确地运行，提高质量而不损伤表面。
6. Smoke Detectors: A Life‑Saving Application | 烟雾探测器：拯救生命的应用
Many household smoke alarms contain a tiny amount of americium‑241, an alpha emitter with a half‑life of 432 years. Inside the detector, alpha particles ionise the air between two electrodes, allowing a small, constant electric current to flow. When smoke enters the chamber, it absorbs the alpha particles and disrupts the ion flow, causing a drop in current that triggers the alarm. Alpha radiation is chosen because it is easily stopped by air and smoke, making the detector highly sensitive to tiny smoke particles. The americium source is securely sealed, and the alpha radiation cannot penetrate the plastic casing or human skin, so it poses no hazard under normal use.
许多家用烟雾报警器含有微量的镅‑241，一种半衰期为 432 年的阿尔法发射体。在探测器内部，阿尔法粒子使两个电极之间的空气电离，从而让微弱而恒定的电流通过。当烟雾进入腔室时，会吸收阿尔法粒子并扰乱离子流，导致电流下降，触发警报。选择阿尔法辐射是因为它很容易被空气和烟雾阻挡，使探测器对微小烟雾颗粒高度敏感。镅源被严密密封，阿尔法辐射无法穿透塑料外壳或人体皮肤，因此在正常使用下没有危害。
7. Carbon‑14 Dating: Uncovering the Past | 碳‑14 定年：揭示过去
Radiocarbon dating uses the radioactive isotope carbon‑14 to determine the age of organic materials up to about 50 000 years old. Living organisms constantly exchange carbon with the atmosphere and maintain the same ratio of C‑14 to stable C‑12. When the organism dies, it stops taking in carbon, and the C‑14 already present decays with a half‑life of approximately 5730 years. By measuring the remaining C‑14 activity in a sample and comparing it with the expected level in a living equivalent, archaeologists can calculate the time that has elapsed since death. This technique has revolutionised archaeology, allowing the dating of ancient bones, wood, parchment and textiles.
放射性碳定年法利用放射性同位素碳‑14 来测定距今约 5 万年的有机物的年代。活着的生物不断与大气进行碳交换，保持 C‑14 与稳定 C‑12 的比例不变。当生物死亡后，它停止摄入碳，而体内原有的 C‑14 发生衰变，半衰期约为 5730 年。通过测定样本中剩余的 C‑14 活度，并与现实活体的预期水平进行比较，考古学家可以计算出生物死亡后所经过的时间。这一技术彻底改变了考古学，使得测定古代骨骼、木材、羊皮纸和纺织品的年代成为可能。
8. Nuclear Power: Generating Electricity from Fission | 核能发电：通过裂变产生电力
Nuclear power stations exploit the energy released during induced nuclear fission. When a neutron is absorbed by a uranium‑235 nucleus, the nucleus splits into two smaller daughter nuclei, releasing two or three more neutrons and a large amount of kinetic energy. The ejected neutrons can go on to cause further fissions, producing a controlled chain reaction. The energy heats a coolant, which turns water into steam that drives a turbine connected to a generator. Control rods (often made of boron) absorb excess neutrons to keep the reaction rate steady, and a moderator (such as water or graphite) slows down neutrons so they can be captured more effectively. Unlike fossil fuels, nuclear fission does not produce greenhouse gases during operation, but it does generate long‑lived radioactive waste.
核电站利用受控核裂变释放的能量。当一个中子被铀‑235 原子核吸收后，原子核分裂成两个较小的子核，同时释放出两到三个中子和大量动能。发射出的中子可以继续引发更多的裂变，形成受控链式反应。释放的能量加热冷却剂，冷却剂将水变为蒸汽，蒸汽驱动连接发电机的涡轮机。控制棒（通常由硼制成）吸收多余的中子以保持反应速率稳定，而慢化剂（如水或石墨）减缓中子的速度，使它们更易被俘获。与化石燃料不同，核裂变在运行过程中不产生温室气体，但会产生长寿命的放射性废物。
9. Managing Radioactive Waste | 放射性废物管理
The operation of nuclear reactors, as well as medical and industrial uses, produces radioactive waste that must be carefully handled. Low‑level waste (contaminated clothing, swabs) is compacted and buried in shallow landfill. Intermediate‑level waste (resins, chemical sludges) requires shielding and is often encased in concrete. High‑level waste, such as spent nuclear fuel, is initially stored in cooling ponds to allow short‑lived isotopes to decay and then may be vitrified – mixed with molten glass and poured into stainless steel containers – for long‑term geological disposal deep underground. The challenge is to isolate these materials from the biosphere for many thousands of years until their activity drops to safe levels.
核反应堆的运行以及医疗和工业用途都会产生放射性废物，必须小心处理。低放废物（受污染的衣物、棉签）经压缩后埋入浅层填埋场。中放废物（树脂、化学污泥）需要屏蔽，通常用混凝土封装。高放废物，如乏核燃料，首先存放在冷却池中，让短寿命同位素衰变，然后可能被玻璃固化——与熔融玻璃混合，浇铸在不锈钢容器中——以便在地下深层进行长期地质处置。挑战在于将这些物质与生物圈隔离数千年，直到其活度降至安全水平。
10. Radiation Safety and Protection | 辐射安全与防护
Anyone working with radioactive sources must follow strict safety procedures based on three principles: time, distance and shielding. Exposure time is kept as short as possible; operations are practised beforehand using non‑radioactive models. Distance is maximised because intensity follows an inverse‑square law; handling tools such as tongs keep sources well away from the body. Appropriate shielding is chosen according to radiation type: thick lead for gamma, Perspex for beta (to avoid X‑rays produced when beta particles strike dense materials), and a sheet of paper or a few centimetres of air for alpha. Regular monitoring with film badges or electronic dosimeters ensures that doses remain within legal limits.
任何接触放射源的人员都必须遵守基于三项原则的严格安全程序：时间、距离和屏蔽。暴露时间尽可能缩短；操作前先用非放射性模型进行演练。距离尽可能远，因为强度遵循平方反比定律；使用钳子等操作工具使源远离身体。根据辐射类型选择合适的屏蔽：伽马射线用厚铅，贝塔粒子用有机玻璃（以避免贝塔粒子撞击致密材料时产生 X 射线），阿尔法粒子用一张纸或几厘米厚的空气即可阻挡。用胶片徽章或电子剂量计进行定期监测，确保剂量保持在法定限值内。
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