📚 Radioactivity and Its Applications | 放射性及其应用
Radioactivity is the spontaneous emission of particles or energy from an unstable nucleus. In IGCSE Edexcel Science, understanding atomic structure, types of radiation, half-life, and safe uses of radiation is essential.
放射性是指不稳定原子核自发释放粒子或能量的现象。在爱德思 IGCSE 科学课程中，理解原子结构、辐射类型、半衰期以及辐射的安全应用至关重要。
1. Atomic Structure and the Nucleus | 原子结构与原子核
The nucleus of an atom contains protons and neutrons. The number of protons is the atomic number (Z), and the total number of protons plus neutrons is the mass number (A).
原子核由质子和中子组成。质子数称为原子序数（Z），质子数和中子数之和称为质量数（A）。
- Protons are positively charged, neutrons are neutral, and electrons orbit the nucleus.
- 质子和中子紧密束缚在核内，电子在核外分层排布。
ₐXᵇ notation: where b = mass number, a = atomic number | 符号ₐXᵇ中，b为质量数，a为原子序数
2. What is Radioactivity? | 什么是放射性？
Some nuclei are unstable because they have too many protons or too many neutrons. To become stable, they emit radiation spontaneously.
有些原子核因质子过多或中子过多而变得不稳定。为了趋于稳定，它们会自发地放出辐射。
- Unstable nuclei are called radioactive.
- 这种不稳定的原子核被称为放射性同位素。
- This process is random and cannot be controlled by physical or chemical conditions.
- 这一过程是随机的，不受物理或化学条件控制。
3. Types of Radiation: Alpha (α), Beta (β), Gamma (γ) | 辐射类型：α、β、γ
Three main types of ionising radiation are emitted by radioactive substances.
放射性物质主要放出三种电离辐射。
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Nature | 本质 | Helium nucleus (2p + 2n) | 氦核（2质子+2中子） | Fast-moving electron | 高速电子 | Electromagnetic wave | 电磁波 |
| Charge | 电荷 | +2 | -1 | 0 |
| Ionising power | 电离能力 | Strong | 强 | Medium | 中等 | Weak | 弱 |
| Penetrating power | 穿透能力 | Stopped by paper or skin | 被纸或皮肤阻挡 | Stopped by a few mm of aluminium | 被几毫米铝片阻挡 | Stopped by thick lead or concrete | 被厚铅或混凝土阻挡 |
4. Ionising Ability and Penetration | 电离能力与穿透力
Alpha particles ionise strongly because they are large and slow-moving, but they are easily absorbed. Gamma rays are the most penetrating because they have no charge and travel at the speed of light.
α粒子体积大、速度慢，因此电离作用最强，但容易被吸收。γ射线不带电荷，以光速传播，因此穿透力最强。
- Greater ionisation leads to greater localised damage.
- 电离越强，对局部细胞的损伤也越大。
- High penetration means gamma can pass through the body.
- 高穿透性意味着γ射线可以穿透人体。
5. Radioactive Decay and Equations | 放射性衰变与方程
When a nucleus decays, it changes into another element. This is represented by balanced nuclear equations.
原子核衰变时会转变为另一种元素，可以用平衡核方程表示。
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
This is an example of alpha decay. The mass number decreases by 4 and the atomic number decreases by 2.
这是α衰变的例子：质量数减少4，原子序数减少2。
¹⁴₆C → ¹⁴₇N + ⁰₋₁e
This is beta decay. A neutron becomes a proton and an electron is emitted; the atomic number increases by 1.
这是β衰变：中子转变为质子并发射电子，原子序数增加1。
6. Half-Life | 半衰期
The half-life of a radioactive isotope is the time taken for half of the radioactive nuclei to decay.
放射性同位素的半衰期是指一半放射性原子核发生衰变所需的时间。
- Half-life is constant for a given isotope.
- 特定同位素的半衰期是恒定的。
- It cannot be changed by temperature, pressure, or chemical state.
- 它不受温度、压力或化学状态的影响。
Remaining amount = Initial amount × (½)ⁿ, where n = number of half-lives | 剩余量 = 初始量 × (½)ⁿ，其中n为半衰期数
7. Background Radiation | 背景辐射
We are always exposed to low-level radiation from natural and man-made sources.
我们始终暴露在来自天然和人为来源的低水平辐射中。
- Natural sources: radon gas from rocks, cosmic rays from space, carbon-14 in living things.
- 天然来源：岩石中的氡气、太空中的宇宙射线、生物体内的碳-14。
- Man-made sources: medical X-rays, nuclear waste, nuclear power tests.
- 人为来源：医疗X射线、核废料、核试验。
When measuring radiation from a sample, background radiation must be subtracted.
测量样品辐射时，必须减去背景辐射。
8. Uses of Radiation | 辐射的应用
Radiation is used safely in medicine, industry, and archaeology.
辐射在医学、工业和考古学中有安全的应用。
| Application | 应用 | Type of radiation | 辐射类型 | Reason | 原因 |
|---|---|---|
| Cancer treatment | 癌症治疗 | Gamma | γ | Kills cancer cells, penetrates body | 杀死癌细胞，穿透人体 |
| Medical imaging | 医学成像 | Gamma | γ | Emitted from tracer, detected outside | 从示踪剂发出，体外检测 |
| Smoke detectors | 烟雾探测器 | Alpha | α | Ionises air, easily stopped by smoke | 电离空气，容易被烟雾阻挡 |
| Carbon dating | 碳定年 | Beta | β | Measures carbon-14 decay in ancient remains | 测量古代遗骸中碳-14的衰变 |
9. Carbon Dating and Half-Life Calculations | 碳定年与半衰期计算
Carbon-14 is absorbed by all living things. When they die, the amount of carbon-14 decreases with a half-life of 5730 years.
所有生物都会吸收碳-14。生物死亡后，碳-14含量以5730年的半衰期减少。
Example: A bone has 25% of the carbon-14 found in a living organism. How old is it?
例：某骨头中碳-14含量是活体的25%。这块骨头有多久历史？
100% → 50% → 25% = 2 half-lives = 2 × 5730 = 11460 years | 100% → 50% → 25% = 2个半衰期 = 2 × 5730 = 11460年
10. Nuclear Fission and Fusion | 核裂变与核聚变
Nuclear fission is the splitting of a heavy nucleus (e.g. uranium-235) when it absorbs a neutron, releasing energy and more neutrons.
核裂变是重原子核（如铀-235）吸收中子后分裂，释放能量和更多中子。
Nuclear fusion is the joining of two light nuclei (e.g. hydrogen isotopes) to form a heavier nucleus, releasing enormous energy.
核聚变是两个轻核（如氢同位素）结合成较重原子核，释放巨大能量。
- Fission is used in nuclear power stations.
- 裂变用于核电站。
- Fusion is the energy source of stars.
- 聚变是恒星的能量来源。
11. Safety and Protection | 安全与防护
To reduce radiation exposure, three principles are applied: time, distance, and shielding.
为减少辐射暴露，需要遵循三个原则：时间、距离和屏蔽。
- Minimise time spent near the source.
- 尽量减少在辐射源附近的时间。
- Use long tongs to increase distance.
- 使用长柄钳增加距离。
- Wear lead aprons or use lead screens.
- 穿戴铅围裙或使用铅屏。
Geiger-Müller tubes are used to detect radiation. Their readings can help measure count rate.
盖革-米勒管用于检测辐射，其读数可帮助测量计数率。
Radioactivity is a central topic in IGCSE Edexcel Science. Understanding types of radiation, decay, half-life, and safe applications allows students to solve exam problems with confidence.
放射性是爱德思 IGCSE 科学的核心主题。理解辐射类型、衰变、半衰期和安全应用，能帮助学生在考试中自信解题。
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