📚 GCSE Edexcel Physics: Nuclear Physics Key Points | GCSE Edexcel 物理：核物理 考点精讲
Nuclear physics is a fundamental topic in the Edexcel GCSE Physics specification, covering the structure of atoms, radioactivity, nuclear radiation, half-life, and nuclear energy. This revision guide highlights the key points and essential knowledge you need for the exam.
核物理是 Edexcel GCSE 物理考纲中的基础主题，涵盖原子结构、放射性、核辐射、半衰期和核能。本考点精讲指出了应对考试所需的关键要点和核心知识。
1. Basic Atomic Structure | 原子结构基础
All matter is made of atoms. An atom consists of a small, dense nucleus surrounded by orbiting electrons. The nucleus contains protons and neutrons, which are collectively called nucleons. Protons have a positive charge, neutrons are neutral, and electrons have a negative charge. Most of the atom’s mass is concentrated in the nucleus.
所有物质由原子构成。原子由一个小而致密的原子核及绕核运动的电子组成。原子核包含质子和中子，两者统称为核子。质子带正电，中子不带电，电子带负电。原子的绝大部分质量集中在原子核上。
The atomic number (Z) is the number of protons in the nucleus, which determines the element. The mass number (A) is the total number of protons and neutrons. Atoms are neutral overall because the number of electrons equals the number of protons.
原子序数 (Z) 是原子核内质子的数目，它决定了元素种类。质量数 (A) 是质子数与中子数的总和。原子整体呈电中性，因为电子数等于质子数。
Key notation: an element X is represented as ᴬZX, or using numeric superscripts and subscripts, e.g. carbon-12 is ¹²₆C. Here 12 is the mass number and 6 is the atomic number.
关键表示法：元素 X 表示为 ᴬZX，或使用数字上下标，例如碳-12写作 ¹²₆C。这里12是质量数，6是原子序数。
2. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers). For example, hydrogen has three isotopes: protium ¹₁H, deuterium ²₁H, and tritium ³₁H.
同位素是指质子数相同（原子序数相同）而中子数不同（质量数不同）的同一种元素的原子。例如，氢有三种同位素：氕 ¹₁H、氘 ²₁H 和氚 ³₁H。
Isotopes share identical chemical properties because chemical behaviour is determined by the number of electrons, which equals the number of protons. However, their physical properties, such as density and stability, can differ. Some isotopes are unstable and radioactive.
同位素具有相同的化学性质，因为化学行为由电子数决定，而电子数等于质子数。但它们的物理性质（如密度和稳定性）可能不同。有些同位素不稳定，具有放射性。
The number of neutrons in an atom can be calculated by subtracting the atomic number from the mass number: N = A – Z.
原子中的中子数可以通过质量数减去原子序数求得：N = A – Z。
3. Radioactive Decay and Types of Nuclear Radiation | 放射性衰变与核辐射类型
Some atomic nuclei are unstable and spontaneously disintegrate to become more stable, emitting radiation in the process. This is called radioactive decay. It is a random process that cannot be influenced by external conditions such as temperature or pressure.
一些原子核不稳定，会自发衰变以便变得更稳定，同时释放出辐射。这个过程称为放射性衰变。这是一个随机过程，不受温度或压力等外部条件的影响。
There are three main types of nuclear radiation: alpha (α) particles, beta (β) particles, and gamma (γ) rays. An alpha particle is a helium nucleus, consisting of two protons and two neutrons (⁴₂He). A beta particle is a fast-moving electron emitted from the nucleus when a neutron turns into a proton (⁰₋₁e). Gamma radiation is high-energy electromagnetic radiation.
核辐射主要有三种类型：α 粒子、β 粒子和 γ 射线。α粒子是一个氦核，由两个质子和两个中子组成 (⁴₂He)。β粒子是原子核内一个中子转变为质子时发射出的高速电子 (⁰₋₁e)。γ辐射是高能电磁辐射。
When a nucleus emits an alpha particle, its mass number decreases by 4 and its atomic number decreases by 2. Beta emission increases the atomic number by 1 while the mass number stays the same. Gamma emission usually accompanies alpha or beta decay; it carries away excess energy without changing the mass or atomic number.
原子核发射一个α粒子时，其质量数减少4，原子序数减少2。β发射使原子序数增加1，而质量数保持不变。γ辐射通常伴随α衰变或β衰变发生，它带走多余的能量，不改变原子核的质量数或原子序数。
4. Properties of Alpha, Beta and Gamma Radiation | α、β、γ 辐射的性质比较
The three types of radiation differ in their penetration power, ionising ability, and behaviour in electric and magnetic fields. The table below summarises these key differences.
这三类辐射的穿透能力、电离能力以及在电场和磁场中的表现各不相同。下表总结了这些关键区别。
| Property / 性质 | Alpha (α) / α粒子 | Beta (β) / β粒子 | Gamma (γ) / γ射线 |
|---|---|---|---|
| Nature / 本质 | Helium nucleus, ⁴₂He / 氦核 | Fast electron, ⁰₋₁e / 高速电子 | Electromagnetic wave / 电磁波 |
| Relative mass / 相对质量 | 4 | ~1/2000 (negligible) / 约1/2000 (可忽略) | 0 |
| Charge / 电荷 | +2e / +2基本电荷 | -1e / -1基本电荷 | 0 (no charge) / 不带电 |
| Ionising power / 电离能力 | Very strong / 很强 | Medium / 中等 | Weak / 弱 |
| Penetration power / 穿透能力 | Stopped by a few cm of air or a sheet of paper / 几厘米空气或纸张即可阻挡 | Stopped by a few mm of aluminium / 几毫米铝板可阻挡 | Reduced by thick lead or concrete; never fully stopped / 厚铅板或混凝土减弱，无法完全阻挡 |
| Deflection in electric/magnetic field / 电场/磁场中的偏转 | Deflected slightly, towards negative plate (positive charge) / 向负极板轻微偏转 (带正电) | Deflected strongly, towards positive plate (negative charge, much smaller mass) / 向正极板大幅偏转 (带负电，质量很小) | No deflection / 不会偏转 |
Because ionising ability is linked to damage to living cells, alpha radiation is the most hazardous inside the body, whereas gamma is the most dangerous from external sources due to its high penetration.
由于电离能力与对活细胞的损伤有关，α辐射在体内危害最大，而γ射线因其穿透力最强，外部照射风险最高。
5. Nuclear Decay Equations | 核衰变方程
Nuclear decay equations show the change in the nucleus. In alpha decay the nucleus loses 2 protons and 2 neutrons, so the mass number drops by 4 and the atomic number by 2. For example, the alpha decay of radium-226:
核衰变方程显示了原子核的变化。在α衰变中，原子核失去2个质子和2个中子，因此质量数减少4，原子序数减少2。例如，镭-226的α衰变：
²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He
In beta-minus decay, a neutron changes into a proton and emits a fast electron. The mass number remains unchanged but the atomic number increases by 1. For example, the beta decay of carbon-14:
在β⁻衰变中，一个中子转变为一个质子并发射出一个高速电子。质量数保持不变，但原子序数增加1。例如，碳-14的β衰变：
¹⁴₆C → ¹⁴₇N + ⁰₋₁e
Gamma decay does not affect the mass number or atomic number, so it is often omitted when writing balanced equations; instead, gamma radiation is added as a separate product alongside the daughter nucleus.
γ衰变不改变质量数或原子序数，因此在书写配平的方程式时通常被省略，γ辐射仅作为与子核并列的产物单独标出。
6. Half-Life | 半衰期
The half-life of a radioactive isotope is the time taken for half of the unstable nuclei in a sample to decay, or equivalently, for the activity (count rate) to fall to half its initial value. Half-life is a constant for a given isotope and is unaffected by physical or chemical conditions.
放射性同位素的半衰期是指样品中一半不稳定原子核发生衰变所需的时间，也就是活度（计数率）降至初始值一半所需的时间。半衰期对于特定同位素是常数，不受物理或化学条件影响。
Radioactive decay is a random process: it is impossible to predict which nucleus will decay next, but the overall pattern of decay is predictable for a large number of nuclei. The relationship between remaining nuclei and half-lives can be expressed as:
放射性衰变是随机过程：无法预测下一个衰变的原子核是哪个，但对于大量原子核而言，总体衰变规律是可预测的。剩余原子核数与半衰期次数的关系可表示为：
Remaining amount = Initial amount × (½)n
where n is the number of half-lives elapsed. For instance, iodine-131 has a half-life of 8 days. After 16 days (2 half-lives), only one quarter of the original radioactive nuclei remains.
其中 n 是经过的半衰期个数。例如，碘-131的半衰期为8天。经过16天（2个半衰期）后，仅剩下四分之一的原始放射性原子核。
7. Background Radiation | 本底
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