📚 IGCSE Physics: Practical Applications of Radioactivity | IGCSE物理：放射性的实际应用
Radioactive isotopes emit radiation that can be harnessed for a wide range of real-world purposes. From treating cancer to dating ancient artefacts, the practical applications of radioactivity rely on the properties of alpha (α), beta (β) and gamma (γ) radiation.
放射性同位素发出的辐射可以被用于多种实际用途。从治疗癌症到测定古代文物的年代，放射性的实际应用都依赖于α、β和γ辐射的特性。
1. Types of Radiation and Their Properties | 辐射类型及其性质
Before exploring applications, it is essential to recall the key properties of the three main types of radiation. Alpha particles are helium nuclei (two protons and two neutrons), they carry a +2 charge, and they are stopped by a sheet of paper or a few centimetres of air. Beta particles are fast-moving electrons, they carry a -1 charge, and they can penetrate a few millimetres of aluminium. Gamma rays are electromagnetic waves, they have no charge, and they can pass through several centimetres of lead.
在探讨应用之前，必须回顾三种主要辐射的关键性质。α粒子是氦原子核（两个质子和两个中子），带+2电荷，能被一张纸或几厘米空气阻挡。β粒子是高速运动的电子，带-1电荷，能穿透几毫米厚的铝。γ射线是电磁波，不带电荷，能穿透数厘米厚的铅。
| Property / 性质 | Alpha (α) / α | Beta (β) / β | Gamma (γ) / γ |
| Nature / 本质 | Helium nucleus / 氦核 | Electron / 电子 | Electromagnetic wave / 电磁波 |
| Charge / 电荷 | +2 | -1 | 0 |
| Penetration / 穿透力 | Paper / 纸张 | Aluminium (mm) / 铝（毫米） | Lead / concrete (cm) / 铅/混凝土（厘米） |
| Ionising ability / 电离能力 | Strong / 强 | Medium / 中等 | Weak / 弱 |
2. Medical Therapy: Cancer Treatment | 医学治疗：癌症放疗
One of the most important medical applications is using gamma radiation to destroy cancer cells. A radioactive source such as cobalt-60 is placed either outside the body, directed at the tumour, or inside the body near the cancer. The gamma rays kill the rapidly dividing cancer cells by damaging their DNA, while normal cells can often repair themselves.
最重要的医学应用之一是使用γ射线摧毁癌细胞。将钴-60等放射源放置在体外对准肿瘤，或放置在体内靠近癌症部位。γ射线通过破坏快速分裂的癌细胞DNA来杀死它们，而正常细胞往往能自我修复。
In a technique called radiotherapy, the radiation dose is carefully planned so that the tumour receives a high dose, while surrounding healthy tissue is protected as much as possible. In internal radiotherapy (‘brachytherapy’), small radioactive seeds are placed directly inside the prostate, cervix or other organs. This delivers a high dose exactly where it is needed.
在称为放疗的技术中，辐射剂量被精心规划，使肿瘤获得高剂量，同时尽可能保护周围健康组织。在内放疗中，将微小的放射性粒子直接植入前列腺、宫颈或其他器官内部。这样可将高剂量精确输送到需要的部位。
3. Medical Diagnosis: Tracers | 医学诊断：示踪剂
Radioactive substances called tracers help doctors examine internal organs and blood flow. A patient is given a small amount of a radioactive isotope, such as technetium-99m, which emits gamma rays that pass out of the body and are detected by a gamma camera. The resulting image shows how the tracer moves through the body.
称为示踪剂的放射性物质可帮助医生检查内部器官和血流。给患者服用少量放射性同位素，如锝-99m，它会发出γ射线，穿透体外后被γ相机探测。所得图像显示示踪剂如何在体内移动。
Doctors use tracers to detect cancer, heart disease and thyroid disorders. For example, iodine-131 is absorbed by the thyroid gland, so its radiation reveals the size and activity of the gland. When choosing a medical tracer, the half-life must be short enough that the radioactivity quickly disappears from the body but long enough to perform the scan.
医生用示踪剂检测癌症、心脏病和甲状腺疾病。例如，碘-131会被甲状腺吸收，因此其辐射可显示腺体的大小和活性。选择医用示踪剂时，半衰期必须足够短，使放射性迅速从体内消失，但又要足够长以便完成扫描。
4. Sterilisation of Medical Equipment | 医疗器械灭菌
Gamma rays are used to sterilise medical instruments, syringes and surgical gloves. Because gamma radiation has a very high penetrating power, it can kill bacteria and other microorganisms even inside sealed packages. This is safer than boiling or using chemicals, because the objects do not become radioactive and can be stored for a long time after sterilisation.
γ射线用于对医疗器械、注射器和外科手套进行灭菌。由于γ辐射具有很强的穿透力，即使密封包装内的细菌和其他微生物也能被杀死。这比煮沸或使用化学品更安全，因为物体不会变得具有放射性，灭菌后可以长期储存。
The items to be sterilised are placed on a conveyor belt and moved past a strong gamma source, commonly cobalt-60. The process is fast, uniform and leaves no toxic residue, making it ideal for single-use medical supplies and for transplant tissues.
待灭菌物品放置在传送带上，经过一个强γ源（通常是钴-60）。该过程快速、均匀且无有毒残留，非常适合一次性医疗用品和移植组织。
5. Industrial Thickness Gauges | 工业测厚仪
In paper mills, metal production and plastic film manufacturing, the thickness of material must be controlled continuously. A beta source and a detector are placed on opposite sides of the sheet. The amount of beta radiation reaching the detector decreases as the material gets thicker, because more radiation is absorbed.
在造纸厂、金属生产和塑料薄膜制造中，必须连续控制材料厚度。将β源和探测器放置在板材两侧。材料越厚，到达探测器的β辐射越少，因为更多辐射被吸收。
The detector signal is fed back to a control system that adjusts the rollers to increase or decrease pressure, keeping the thickness constant. This application uses beta particles rather than alpha or gamma: alpha would be stopped too easily, while gamma would pass through too much to give a sensitive measurement.
探测器信号反馈给控制系统，调节滚轮以增加或减小压力，从而使厚度保持恒定。这一应用使用β粒子而非α或γ：α粒子太容易被阻挡，而γ粒子穿透过多，难以提供灵敏的测量。
6. Smoke Detectors | 烟雾探测器
Ionisation smoke detectors contain a tiny amount of americium-241, which emits alpha particles. The alpha particles ionise the air in a small gap between two electrodes, creating a small electrical current. If smoke enters the gap, it absorbs the alpha particles and reduces the ionisation, so the current drops and the alarm sounds.
电离烟雾探测器含有微量的镅-241，它发射α粒子。α粒子使两个电极之间小空隙中的空气电离，产生微弱电流。如果烟雾进入空隙，会吸收α粒子并减少电离，使电流下降，警报随即响起。
Alpha radiation is chosen because it has a very short range in air and is easily absorbed by smoke particles, so the detector can be small and safe. The americium source is sealed, but its activity is so low that it poses no risk to people as long as the detector is not tampered with.
选择α辐射是因为它在空气中的射程很短，容易被烟雾粒子吸收，因此探测器可以小巧且安全。镅源是密封的，其活度极低，只要探测器不被拆开，就不会对人造成危害。
7. Agriculture and Food Preservation | 农业与食品保鲜
Gamma radiation is used to irradiate food, killing insects, bacteria and parasites that cause spoilage. Irradiated potatoes and onions are also prevented from sprouting, so they can be stored for much longer. This process does not make the food radioactive, and many health agencies consider it safe.
γ辐射用于对食品进行辐照，杀死导致变质的昆虫、细菌和寄生虫。辐照后的土豆和洋葱还可防止发芽，从而延长储存时间。该过程不会使食物产生放射性，许多健康机构认为这是安全的。
In agriculture, radiation is used to produce crop mutations. Seeds are exposed to gamma rays to create genetic changes, and the resulting plants may have useful traits such as higher yield, disease resistance or better drought tolerance. This technique has created many improved crop varieties around the world.
在农业中，辐射用于诱发作物突变。将种子暴露在γ射线下产生基因变化，所得植物可能具有高产、抗病或更耐旱等优良性状。这项技术已在世界各地培育出许多改良作物品种。
8. Carbon Dating | 碳定年
Carbon-14 is a radioactive isotope that is constantly formed in the atmosphere and absorbed by all living things. While an organism is alive, the ratio of carbon-14 to carbon-12 in its body stays constant. After death, no new carbon-14 is taken in, and the existing carbon-14 decays into nitrogen-14 with a half-life of 5730 years.
碳-14是一种在大气中不断生成并被所有生物吸收的放射性同位素。当生物体活着时，其体内碳-14与碳-12的比例保持恒定。死亡后，不再吸收新的碳-14，原有碳-14以5730年的半衰期衰变成氮-14。
By measuring the remaining proportion of carbon-14 in an ancient bone or piece of wood, scientists can estimate how long ago the organism died. The age can be calculated from the decay equation:
通过测量古代骨骼或木材中剩余的碳-14比例，科学家可以估算生物死亡的时间。年龄可根据衰变方程计算：
t = (T½ / ln 2) × ln(N₀ / N)
where T½ is the half-life, N₀ is the original amount of carbon-14 and N is the amount remaining. For IGCSE, the key point is that this method works for objects that were once alive and are up to about 50 000 years old.
其中T½是半衰期，N₀是碳-14原始含量，N是剩余含量。就IGCSE而言，关键是这种方法适用于曾经有生命的物体，最远可测约5万年前。
9. Nuclear Power Generation | 核能发电
In a nuclear power station, uranium-235 nuclei undergo fission: absorbing a neutron makes the nucleus split into two smaller nuclei, releasing a large amount of energy and more neutrons. These neutrons go on to split further nuclei, producing a controlled chain reaction. The heat generated is used to convert water into steam, which drives a turbine to generate electricity.
在核电站中，铀-235原子核发生裂变：吸收一个中子后，原子核分裂成两个较小的原子核，释放大量能量和更多中子。这些中子继续分裂其他原子核，产生受控的链式反应。所产生的热量用于将水转化为蒸汽，蒸汽驱动涡轮机发电。
Nuclear power produces no carbon dioxide during operation, which is a major advantage over fossil fuels. However, it produces radioactive waste that must be stored safely for thousands of years. This is an important debate in modern energy policy.
核电在运行期间不产生二氧化碳，这是相对化石燃料的一大优势。然而，它产生的放射性废物必须安全储存数千年。这是现代能源政策中的一个重要争议。
10. Safety and Handling | 安全与防护
Because radiation can damage living cells, anyone working with radioactive materials must follow strict safety rules. The three basic principles are time, distance and shielding. Minimising time near a source, maximising distance from it, and placing shielding between the source and the body all reduce the absorbed dose.
因为辐射会损伤活细胞，任何接触放射性材料的人都必须遵守严格的安全规则。三个基本原则是时间、距离和屏蔽。缩短靠近源的时间、增大与源的距离、在源和人体之间设置屏蔽，都能减少吸收剂量。
Different types of radiation require different shielding: alpha particles are stopped by paper or even the outer layer of skin, so the main danger is if they are inhaled or ingested; beta particles require a few millimetres of aluminium; gamma rays need thick lead or concrete. Radiation badges are worn by workers to monitor their exposure.
不同类型的辐射需要不同的屏蔽：α粒子能被纸张甚至皮肤外层阻挡，因此主要危险是吸入或摄入；β粒子需要几毫米铝屏蔽；γ射线需要厚铅或混凝土。工作人员佩戴辐射徽章以监测其受照剂量。
11. Summary of Applications | 应用总结
The table below summarises the practical uses covered in this article, along with the type of radiation chosen and the reason for that choice.
下表总结了本文涵盖的实际用途、所选辐射类型及选择理由。
| Application / 应用 | Radiation / 辐射 | Reason / 理由 |
| Cancer treatment / 癌症治疗 | Gamma / γ | High penetration, destroys cells / 穿透力强，摧毁细胞 |
| Medical tracers / 医用示踪剂 | Gamma / γ | Leaves the body, easily detected / 容易排出体外，易被探测 |
| Sterilisation / 灭菌 | Gamma / γ | Penetrates packaging / 穿透包装 |
| Thickness gauge / 测厚仪 | Beta / β | Absorption varies with thickness / 吸收随厚度变化 |
| Smoke detector / 烟雾探测器 | Alpha / α | Ionises air easily, short range / 易电离空气，射程短 |
| Carbon dating / 碳定年 | Beta (from C-14) / β（来自碳-14） | Known half-life, present in living things / 半衰期已知，存在于生物中 |
| Nuclear power / 核能 | Neutron-induced fission / 中子诱发裂变 | Large energy release from uranium-235 / 铀-235释放大量能量 |
Understanding these applications helps us appreciate both the benefits and the responsibilities of using radioactive materials. In every case, the choice of radiation type depends on balancing penetration, ionisation and half-life with the specific need, while always prioritising safety.
理解这些应用有助于我们认识使用放射性材料的好处与责任。在每种情况下，辐射类型的选择都需要根据具体需求，在穿透力、电离能力和半衰期之间取得平衡，并始终将安全放在首位。
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