Radioactivity: Types, Properties and Uses | 放射性：类型、性质与应用

📚 Radioactivity: Types, Properties and Uses | 放射性：类型、性质与应用

Radioactivity is a natural and spontaneous process in which unstable atomic nuclei lose energy by emitting radiation. This phenomenon has profound applications in medicine, energy production, and industry. Understanding the nature of alpha, beta, and gamma radiation is essential for mastering IGCSE science and for recognising how radioactive materials are handled safely in the real world.

放射性是一种自然自发的过程，不稳定的原子核通过发射辐射来释放能量。这一现象在医学、能源生产和工业中具有深远应用。理解 α、β 和 γ 辐射的本质是掌握 IGCSE 科学的关键，也有助于认识现实生活中如何安全处理放射性物质。

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1. Introduction to Radioactivity | 放射性简介

Radioactivity was first discovered by Henri Becquerel in 1896, and later studied by Marie and Pierre Curie. It occurs because some atomic nuclei contain an unstable combination of protons and neutrons. To become more stable, the nucleus emits energy in the form of particles or electromagnetic waves. This emission is called radioactive decay, and it transforms the original nuclide into a different element or isotope.

放射性由亨利·贝克勒尔于 1896 年首次发现，随后由玛丽·居里和皮埃尔·居里深入研究。放射性之所以发生，是因为某些原子核含有不稳定的质子和中子组合。为了变得更稳定，原子核会以粒子或电磁波的形式释放能量。这种释放称为放射性衰变，它将原来的核素转变为不同的元素或同位素。

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2. Types of Nuclear Radiation | 核辐射的类型

There are three main types of nuclear radiation emitted from radioactive substances: alpha (α) particles, beta (β) particles, and gamma (γ) rays. Each type differs in terms of its nature, charge, mass, ionising ability, and penetrating power. Some nuclei also emit neutrons, but for IGCSE we focus on α, β, and γ.

放射性物质主要发射三种类型的核辐射：α 粒子、β 粒子和 γ 射线。每种类型在本质、电荷、质量、电离能力和穿透能力方面各不相同。某些原子核还会发射中子，但在 IGCSE 中我们重点学习 α、β 和 γ。

Property	Alpha (α)	Beta (β)	Gamma (γ)
Nature	Helium nucleus (⁴₂He)	Fast electron (⁰₋₁e)	Electromagnetic wave
Charge	+2	‑1	0 (neutral)
Relative mass	4	1/1836 (negligible)	0
Ionising ability	Very strong	Moderate	Weak
Penetrating power	Stopped by paper or a few cm of air	Stopped by a few mm of aluminium	Reduced by several cm of lead or metres of concrete

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3. Alpha Particles (α) | α 粒子

An alpha particle consists of two protons and two neutrons, identical to a helium‑4 nucleus. It is emitted during alpha decay, which typically occurs in very heavy nuclei such as uranium‑238. Because of its relatively large mass and +2 charge, an alpha particle interacts strongly with atoms along its path, causing intense ionisation over a very short range.

α 粒子由两个质子和两个中子组成，与氦‑4 原子核相同。它在 α 衰变过程中发射，通常发生在铀‑238 等极重的原子核中。由于 α 粒子质量相对较大并带有 +2 电荷，它会与路径上的原子发生强烈相互作用，在很短的距离内造成强烈的电离。

Alpha particles can be stopped by a sheet of paper or a few centimetres of air. They travel only a few centimetres in air and cannot penetrate human skin. However, if an alpha‑emitting substance is ingested or inhaled, the intense local ionisation can cause severe biological damage.

α 粒子可以被一张纸或几厘米的空气阻挡。它们在空气中只能行进几厘米，无法穿透人体皮肤。然而，一旦吞入或吸入发射 α 粒子的物质，局部强烈的电离效应可能对生物体造成严重伤害。

Example decay: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He

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4. Beta Particles (β) | β 粒子

A beta particle is a high‑speed electron ejected from the nucleus when a neutron transforms into a proton. This process increases the atomic number by one while keeping the mass number unchanged. Beta particles are much lighter than alpha particles and carry a single negative charge, so they cause less ionisation per unit length of travel.

β 粒子是原子核内的一个中子转变为质子时射出的高速电子。这一过程使原子序数增加 1，而质量数保持不变。β 粒子的质量远小于 α 粒子，并带有一个负电荷，因此它们在单位行进长度上产生的电离较少。

Beta particles can travel several metres in air and require a few millimetres of aluminium to be absorbed. They can penetrate skin and living tissue to a shallow depth, which makes them hazardous for external exposure, although less so than alpha emitters inside the body.

β 粒子可以在空气中行进数米，需要几毫米厚的铝板才能被吸收。它们可以穿透皮肤并进入活体组织浅层，因此外部照射也具有一定危险性，但相比于体内的 α 放射源来说危害较小。

Example decay: ¹⁴₆C → ¹⁴₇N + ⁰₋₁e

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5. Gamma Rays (γ) | γ 射线

Gamma radiation is a form of high‑energy electromagnetic wave with no mass and no charge. It is emitted when a nucleus has excess energy, often after an alpha or beta decay has left it in an excited state. Gamma rays are the most penetrating type of nuclear radiation and are only partially absorbed by thick lead or several metres of concrete.

γ 辐射是一种高能电磁波，没有质量，也不带电荷。当原子核处于较高能态时，通常在一次 α 或 β 衰变后以激发态形式剩余能量，这时会发射 γ 射线。γ 射线是穿透能力最强的核辐射类型，只能被厚铅板或数米混凝土部分吸收。

Because gamma rays are weakly ionising, they pass through the human body with a lower probability of causing direct damage to individual cells compared with alpha particles. Nevertheless, their high penetration makes shielding a critical safety measure.

由于 γ 射线电离能力较弱，相较于 α 粒子，它们穿过人体时直接损伤细胞的概率较低。然而，其强穿透力使得屏蔽措施成为关键的安全手段。

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6. Ionising Ability | 电离能力

Ionising ability refers to how easily radiation can knock electrons out of atoms, creating ions. Alpha particles have the highest ionising power because of their large mass and +2 charge; they lose energy quickly and produce a dense trail of ions. Beta particles produce fewer ions per millimetre, while gamma rays, being uncharged, interact only occasionally and produce sparse ions.

电离能力指的是辐射将电子从原子中击出、产生离子的难易程度。α 粒子因具有较大质量和 +2 电荷而拥有最强的电离能力；它们迅速损失能量并形成密集的离子径迹。β 粒子每毫米产生的离子较少，而 γ 射线由于不带电荷，仅偶尔发生相互作用，产生稀疏的离子。

This property explains why alpha radiation is so damaging if a source enters the body. The concentrated ionisation can break chemical bonds in DNA, leading to mutations or cell death. In contrast, gamma radiation is often used in radiotherapy precisely because it can deliver energy deep inside the body with less surface ionisation.

这一性质解释了为什么 α 辐射一旦进入体内就会造成极大伤害。集中电离效应会破坏 DNA 中的化学键，导致突变或细胞死亡。相反，γ 辐射常用于放射治疗，正是因为其能将能量传递到身体深处，而表面电离较少。

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7. Penetrating Power | 穿透能力

Penetrating power is inversely related to ionising ability: the more ionising the radiation, the faster it loses energy and the shorter its range. Alpha particles are stopped by paper, beta particles by aluminium, and gamma rays are only significantly attenuated by lead or thick concrete. This relationship guides the choice of materials for shielding in laboratories and nuclear facilities.

穿透能力与电离能力成反比：电离能力越强的辐射，能量损失越快，射程越短。α 粒子可被纸阻挡，β 粒子可被铝板阻挡，而 γ 射线只能被铅或厚混凝土显著衰减。这一关系指导着实验室和核设施中屏蔽材料的选择。

For example, workers handling beta‑emitting isotopes wear thin Perspex or aluminium shields, whereas those working near gamma sources require heavy lead aprons and remote‑handling tools. Understanding penetrating power also helps in selecting the appropriate isotope for medical imaging or industrial gauging.

例如，处理 β 放射源的工作人员会佩戴薄有机玻璃或铝制防护屏，而在 γ 源附近工作则需要穿着厚重的铅围裙并使用远程操作工具。理解穿透能力也有助于为医学成像或工业测量选择合适的同位素。

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8. Detecting Radiation | 探测辐射

Radiation cannot be seen, heard, or felt; it must be detected using instruments. The most common detector is a Geiger‑Müller (GM) tube connected to a counter. When radiation enters the tube, it ionises the gas inside, producing a brief pulse of current that is counted electronically. The count rate, measured in counts per second or per minute, indicates the activity of the source.

辐射看不见、听不见、也感觉不到，必须使用仪器进行探测。最常见的探测器是连接至计数器的盖革‑弥勒（GM）管。当辐射进入管内，会使管内气体电离，产生短暂的电流脉冲，并由电子装置计数。计数率以每秒或每分钟的计数表示，可指示放射源的活度。

Other detection methods include photographic film, which darkens when exposed to radiation, and cloud chambers, where the tracks of ionising particles become visible as vapour trails. In IGCSE experiments, students often measure the absorption of different types of radiation using a GM tube and absorbers such as paper, aluminium, and lead.

其他探测方法包括照相胶片（受辐射照射后会变黑）和云室（电离粒子的径迹在其中显现为雾状轨迹）。在 IGCSE 实验中，学生经常使用 GM 管以及纸、铝板和铅等吸收体来测量不同辐射类型的吸收情况。

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9. Using Radioactivity in Medicine | 放射性在医学中的应用

Radioactive isotopes play a vital role in diagnosis and therapy. Technetium‑99m, a gamma emitter with a short half‑life, is widely used as a medical tracer. It is injected into the bloodstream and accumulates in specific organs; a gamma camera then detects the emitted radiation to create images. This helps doctors assess organ function without invasive surgery.

放射性同位素在诊断和治疗中起着至关重要的作用。锝‑99m 是一种半衰期短的 γ 放射源，被广泛用作医学示踪剂。它被注射到血液中，并在特定器官中积聚；γ 相机随后探测所发射的辐射以生成图像。这有助于医生评估器官功能，而无需进行侵入性手术。

For cancer treatment, high‑energy gamma rays from cobalt‑60 or linear accelerators are focused on tumours to destroy malignant cells. Iodine‑131, a beta and gamma emitter, is used to treat thyroid cancer because the thyroid gland naturally absorbs iodine. Radioactive implants (brachytherapy) can also deliver a high dose directly to a tumour while sparing nearby healthy tissue.

在癌症治疗中，来自钴‑60 或直线加速器的高能 γ 射线被聚焦于肿瘤，以杀灭恶性肿瘤细胞。碘‑131 是一种 β 和 γ 放射源，用于治疗甲状腺癌，因为甲状腺天然会吸收碘。放射性植入物（近距离放射治疗）也能直接向肿瘤提供高剂量辐射，同时保护附近的健康组织。

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10. Using Radioactivity in Industry | 放射性在工业中的应用

In industry, radioisotopes are used for non‑destructive testing, thickness monitoring, and sterilisation. Gamma radiography works similarly to X‑ray imaging: a gamma source is placed on one side of a metal weld or pipe, and a detector on the other side captures the transmitted radiation. Any cracks or voids appear as darker regions on the image, allowing engineers to identify faults without dismantling equipment.

在工业中，放射性同位素用于无损检测、厚度监测和灭菌。γ 射线照相术的工作原理类似于 X 射线成像：将 γ 源放置在金属焊缝或管道的一侧，另一侧的探测器则捕捉透射的辐射。任何裂缝或孔隙在图像上呈现为较暗的区域，使工程师无需拆卸设备即可识别缺陷。

Beta sources are used in thickness gauges for paper, plastic, or metal foil production. The amount of radiation passing through the material depends on its thickness; if the reading changes, the rollers adjust automatically. Gamma sources such as americium‑241 are used in smoke detectors, where the radiation ionises air in a small chamber, and smoke particles disrupt the current, triggering the alarm.

β 源用于纸张、塑料或金属箔生产中的厚度测量仪。穿过材料的辐射量取决于其厚度；如果读数发生变化，滚轴会自动调整。镅‑241 等 γ 源用于烟雾探测器中，辐射使小室内的空气电离，而烟雾颗粒会干扰电流，从而触发警报。

Sterilisation of medical equipment and food packaging is another major application. Intense gamma irradiation kills bacteria, fungi, and insects without leaving any chemical residue. This process is widely used for syringes, surgical gloves, and some spices.

医疗器械和食品包装的灭菌是另一项重要应用。强 γ 辐照能杀灭细菌、真菌和害虫，而不留下任何化学残留物。该工艺广泛用于注射器、手术手套和某些香料的灭菌。

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11. Half‑Life | 半衰期

The half‑life of a radioactive isotope is the time taken for half of the nuclei in a sample to decay. It is a constant property of each isotope and cannot be altered by temperature, pressure, or chemical reactions. Half‑life values range from fractions of a second to billions of years. Knowing the half‑life helps scientists predict how long a source will remain hazardous or how useful it will be in a particular application.

放射性同位素的半衰期是指样品中一半原子核发生衰变所需的时间。它是每种同位素的固有属性，不受温度、压力或化学反应的影响。半衰期数值从不到一秒到数十亿年不等。了解半衰期有助于科学家预测放射源保持危险性的时间，或其在特定应用中的使用寿命。

For medical tracers, a short half‑life (e.g. 6 hours for technetium‑99m) is desirable because the patient’s radiation exposure is limited while still allowing time for imaging. For industrial gauges, a longer half‑life (e.g. 5.27 years for cobalt‑60) ensures a stable source over many years. The decay of a radioactive substance always follows an exponential pattern, which can be represented in graphs and calculations.

对于医学示踪剂，短半衰期（例如锝‑99m 的 6 小时）是理想的，因为患者的辐射暴露有限，同时仍有足够的时间进行成像。对于工业测量计，较长的半衰期（例如钴‑60 的 5.27 年）可确保多年内放射源稳定。放射性物质的衰变始终遵循指数规律，这可用图形和计算来表示。

Decay formula: N = N₀ (½)^(t / T₁/₂)

Where N is the remaining number of nuclei, N₀ is the initial number, t is the time elapsed, and T₁/₂ is the half‑life. This equation allows the prediction of remaining activity after a given time.

其中，N 为剩余的原子核数，N₀ 为初始原子核数，t 为所经过的时间，T₁/₂ 为半衰期。该方程可用于预测经过给定时间后剩余的活度。

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12. Safety Precautions | 安全预防措施

Handling radioactive materials requires strict safety protocols to minimise exposure. The three fundamental principles are time, distance, and shielding. Reducing the time spent near a source limits the accumulated dose; increasing distance dramatically lowers the intensity (inverse square law); and using appropriate shielding absorbs radiation before it reaches the body.

处理放射性材料需要严格的安全规程，以最大限度地减少暴露。三项基本原则是时间、距离和屏蔽。缩短在辐射源附近停留的时间可限制累积剂量；增大距离可显著降低强度（平方反比定律）；使用适当的屏蔽材料可在辐射到达人体之前将其吸收。

In the laboratory, sources are stored in lead‑lined containers and handled with long‑handled tongs. The source should never be pointed at anyone, and it should be kept at arm’s length. After use, hands must be washed thoroughly. In nuclear power plants and research facilities, workers wear dosimeters to monitor their accumulated exposure, and strict legal limits ensure safety.

在实验室中，放射源存放在铅衬容器中，并使用长柄钳操作。源不得指向任何人，并应保持在一臂远的距离。使用后必须彻底洗手。在核电站和研究设施中，工作人员佩戴剂量计以监测累积暴露量，严格的法律限值确保安全。

Waste disposal is equally important. Low‑level radioactive waste is often sealed in containers and buried in designated sites. High‑level waste, such as spent nuclear fuel, requires long‑term storage under controlled conditions. Understanding these precautions not only meets IGCSE learning outcomes but also promotes responsible scientific literacy.

废物处理同样重要。低放射性废物通常密封在容器中，并掩埋在指定场址。高放射性废物（例如乏核燃料）则需要在受控条件下进行长期贮存。理解这些预防措施不仅满足 IGCSE 学习要求，也有助于培养负责任的科学素养。

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