📚 IGCSE AQA Physics: Particle Physics Exam Tips | IGCSE AQA 物理：粒子物理 考点精讲
Particle physics opens up the subatomic world, explaining what everything is made of and how unstable nuclei behave. For IGCSE AQA Physics, you must understand atomic structure, types of radiation, half-life, nuclear reactions and their real-world applications. This revision guide covers all the essential points with clear explanations and paired Chinese translations to boost your confidence for the exam.
粒子物理打开了亚原子世界的大门，解释了万物的组成以及不稳定原子核的行为。针对 IGCSE AQA 物理考试，你必须掌握原子结构、辐射类型、半衰期、核反应及其实际应用。本复习指南覆盖所有核心考点，配有清晰的中英双语解释，帮助你在考试中信心倍增。
1. Atomic Structure | 原子结构
Atoms consist of a small, dense nucleus surrounded by electrons. The nucleus contains protons and neutrons, collectively called nucleons. Protons carry a positive charge (+1 relative charge), neutrons are neutral, and electrons are negative (-1). The relative masses are: proton = 1, neutron = 1, electron = 1/1836 (often taken as 0).
原子由一个微小致密的原子核及绕核运动的电子构成。原子核包含带正电的质子（相对电荷 +1）和不带电的中子，质子和中子统称核子。电子带负电（相对电荷 -1）。相对质量：质子 = 1，中子 = 1，电子 = 1/1836（通常近似为 0）。
In nuclide notation, the mass number (A) is the total number of protons and neutrons, written as a superscript. The atomic number (Z) is the number of protons, written as a subscript. For a neutral atom, the number of electrons equals the number of protons. Example: carbon-12 is written as ¹²₆C.
在核素符号中，质量数（A）是质子与中子总数，写在上标位置；原子序数（Z）是质子数，写在下标位置。中性原子中电子数等于质子数。例如碳-12 写作 ¹²₆C。
2. Isotopes | 同位素
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Therefore, they have the same atomic number (Z) but different mass numbers (A). Chemical properties of isotopes are identical because electrons are unchanged, but their nuclear stability can differ greatly.
同位素是同一元素中质子数相同而中子数不同的原子。因此它们具有相同的原子序数（Z），但质量数（A）不同。同位素的化学性质相同（电子排布不变），但核稳定性可能差异极大。
Many isotopes are unstable and are called radioisotopes. They undergo radioactive decay to become more stable, emitting radiation. For example, carbon-12 (¹²₆C) is stable, while carbon-14 (¹⁴₆C) is radioactive, used in dating archaeological objects.
许多同位素不稳定，称为放射性同位素。它们发生放射性衰变以变得更稳定，同时发出辐射。例如碳-12（¹²₆C）是稳定的，而碳-14（¹⁴₆C）具有放射性，用于考古定年。
3. Radioactive Decay | 放射性衰变
Radioactive decay is a random process by which an unstable nucleus loses energy by emitting ionising radiation. It is spontaneous and cannot be influenced by temperature, pressure or chemical bonding. The rate of decay is unaffected by external conditions.
放射性衰变是一种随机过程，不稳定原子核通过发出电离辐射来释放能量。衰变是自发的，不受温度、压强或化学键影响。衰变速率不受外界条件干扰。
There are three main types of radiation emitted: alpha (α), beta (β) and gamma (γ) rays. Each has different nature, charge, penetrating power and ionising ability. A nucleus may undergo one or more decay stages before reaching a stable form. The original nucleus is called the parent nuclide, and the resulting nucleus is the daughter nuclide.
辐射主要有三种：α 射线、β 射线和 γ 射线。它们的本质、电荷、穿透能力和电离能力各不相同。一个原子核在达到稳定形式前可能需要经历一步或多步衰变。原来的核称为母核，新生成的核称为子核。
4. Alpha Decay | α 衰变
Alpha decay occurs when an unstable nucleus emits an alpha particle, which consists of two protons and two neutrons – identical to a helium nucleus (⁴₂He). This reduces the mass number by 4 and the atomic number by 2. The daughter nucleus is a different element.
α 衰变是指不稳定原子核放出一个 α 粒子，由两个质子和两个中子组成，等同于一个氦原子核（⁴₂He）。该过程使质量数减少 4，原子序数减少 2。子核变为另一种元素。
Example: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
例子：²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
Alpha particles are highly ionising but have low penetrating power. They can be stopped by a few centimetres of air or a thin sheet of paper. They are very dangerous if inhaled or ingested because they cause intense localised damage inside the body.
α 粒子电离能力强，但穿透能力弱。几厘米空气或一张薄纸就能阻挡它们。α 粒子若被吸入或摄入体内，非常危险，因为会在体内造成强烈的局部损伤。
5. Beta Decay | β 衰变
Beta decay involves the transformation of a neutron into a proton (or vice versa) inside the nucleus, with the emission of a beta particle – a fast-moving electron (β⁻) or positron (β⁺). In β⁻ decay, a neutron changes into a proton, emitting an electron and an antineutrino. The mass number stays the same, but the atomic number increases by 1.
β 衰变是原子核内一个中子转变为质子（或相反），同时放出一个高速运动的电子（β⁻）或正电子（β⁺）。在 β⁻ 衰变中，一个中子转变为质子，释放出一个电子和一个反中微子。质量数不变，原子序数增加 1。
Example: ¹⁴₆C → ¹⁴₇N + ⁰₋₁e
例子：¹⁴₆C → ¹⁴₇N + ⁰₋₁e
Beta particles have medium penetrating power and medium ionising ability. They can travel through paper but are stopped by a few millimetres of aluminium. In nuclear equations, both mass number and atomic number must balance on both sides of the equation.
β 粒子具有中等的穿透能力和电离能力。它们能穿透纸张，但几毫米厚的铝片就能阻挡。在核方程中，方程两侧的质量数和原子序数都必须平衡。
6. Gamma Radiation | γ 辐射
Gamma radiation is a form of electromagnetic wave with very high frequency and energy. It is emitted by a nucleus that has excess energy, often after alpha or beta decay. Gamma emission does not change the atomic number or mass number; the nucleus simply loses energy and becomes more stable.
γ 辐射是一种频率极高、能量极大的电磁波。它由拥有过量能量的原子核（常在 α 或 β 衰变后）放出。发射 γ 射线不会改变原子序数或质量数，原子核只是失去能量变得更加稳定。
Gamma rays are weakly ionising but extremely penetrating. They require thick lead or several metres of concrete to be significantly reduced in intensity. In nuclear equations, gamma is usually not written as a particle, but sometimes symbolised as ⁰₀γ.
γ 射线的电离能力很弱，但穿透能力极强。需要厚铅板或数米厚的混凝土才能明显减弱其强度。在核方程中，γ 通常不写作粒子，有时用符号 ⁰₀γ 表示。
7. Penetrating Power and Ionising Ability | 穿透能力与电离能力
The three types of radiation can be distinguished by their behaviour in electric and magnetic fields. Alpha particles (positive) are deflected slightly towards the negative plate; beta particles (negative) are deflected strongly towards the positive plate; gamma rays have no charge and are undeflected.
三种辐射可通过它们在电场和磁场中的行为加以区分。带正电的 α 粒子稍向负极板偏转；带负电的 β 粒子向正极板大幅偏转；γ 射线因不带电而不发生偏转。
Ionising ability is linked to damage in living cells. Alpha is the most ionising, beta is intermediate, and gamma is the least ionising. However, gamma’s high penetration makes it dangerous externally, while alpha is an internal hazard. Understanding this balance helps in choosing radiation for medical or industrial uses.
电离能力与对活细胞的伤害相关。α 电离最强，β 次之，γ 最弱。然而，γ 的高穿透性使其对外部威胁较大，而 α 是内部危害。理解这种平衡有助于选择医疗或工业用辐射。
| Radiation | Nature | Penetration stopped by | Ionising power |
| Alpha (α) | Helium nucleus | Paper, few cm air | Very high |
| Beta (β) | Electron/positron | 3-5 mm aluminium | Medium |
| Gamma (γ) | EM wave | Thick lead, concrete | Low |
中文对照：
| 辐射 | 本质 | 被…阻挡 | 电离能力 |
| α | 氦核 | 纸张、几厘米空气 | 很强 |
| β | 电子/正电子 | 3-5 毫米铝 | 中等 |
| γ | 电磁波 | 厚铅、混凝土 | 弱 |
8. Half-Life | 半衰期
Half-life is the time taken for the number of radioactive nuclei in a sample to halve. Alternatively, it is the time for the count rate or activity to fall to half its initial value. Every radioisotope has a fixed half-life. This is unaffected by physical conditions or chemical combination.
半衰期是样品中放射性原子核数量减半所需的时间。也可以定义为计数率或活度降至初始值一半所需的时间。每种放射性同位素都有固定的半衰期，不受物理条件或化学结合的影响。
Half-life calculations involve either step-by-step halving or using a decay curve. If a sample starts with 1000 undecayed nuclei and has a half-life of 2 hours, after 2 hours 500 remain, after 4 hours 250 remain, and so on. Half-life problems often require reading graphs or applying simple ratios.
半衰期的计算可采用逐步减半法或衰变曲线法。如果一个样品开始有 1000 个未衰变核，半衰期为 2 小时，则 2 小时后剩 500 个，4 小时后剩 250 个，以此类推。半衰期问题常需读取图表或运用简单比例。
The concept of half-life is vital for radioactive dating, such as carbon-14 dating to determine the age of organic remains, and for designing safe storage times for nuclear waste.
半衰期的概念在放射性定年中至关重要，例如碳-14 定年法可用来确定有机遗骸的年代，也可用于设计核废料的安全储存时间。
9. Background Radiation | 背景辐射
Background radiation is the low-level radiation that is always present in the environment. Sources include cosmic rays from space, naturally occurring radioactive materials in rocks and soil (such as radon gas), and man-made sources like medical X-rays and nuclear power.
背景辐射是环境中始终存在的低水平辐射。其来源包括来自太空的宇宙射线，岩石和土壤中天然存在的放射性物质（例如氡气），以及人工来源如医疗 X 射线和核能。
Background count rate must be measured and subtracted from experimental readings when investigating radioactive sources. In the UK, about half of the annual dose comes from radon gas. This radiation is unavoidable and is part of our natural environment.
在探究放射源时，必须测量背景辐射计数率，并从实验读数中扣除。在英国，约一半的年辐射剂量来自氡气。这种辐射是无法避免的天然环境的一部分。
10. Nuclear Fission and Fusion | 核裂变与核聚变
Nuclear fission is the splitting of a large, unstable nucleus (e.g. uranium-235 or plutonium-239) after absorbing a neutron. The nucleus splits into two smaller daughter nuclei, releasing two or three fast neutrons and a huge amount of energy. The neutrons can trigger further fission events, leading to a chain reaction.
核裂变是大质量不稳定核（如铀-235 或钚-239）吸收中子后分裂的过程。核分裂为两个较小的子核，同时释放出两到三个快中子和巨大能量。这些中子可以引发进一步的裂变，形成链式反应。
Nuclear fusion is the joining of two light nuclei, such as hydrogen isotopes, to form a heavier nucleus. This process releases even more energy than fission. Fusion occurs in stars, where extreme temperature and pressure overcome the electrostatic repulsion between positively charged nuclei. Controlled fusion on Earth remains a major scientific challenge.
核聚变是两个轻核（如氢的同位素）结合成一个较重核的过程。聚变释放的能量比裂变更大。恒星中发生核聚变，那里的极高温度和压力克服了正电核之间的静电斥力。在地球上实现可控聚变仍是一项重大科学挑战。
Fission is used in nuclear power stations to generate electricity; fusion holds promise for clean, abundant energy but is not yet commercially viable.
裂变用于核电站发电；聚变则有望提供清洁、丰富的能源，但尚未实现商业化。
11. Applications of Radioactivity | 放射性的应用
Radioactivity has many practical uses depending on the penetrating power and half-life of the source. In medicine, gamma rays are used for radiotherapy to kill cancer cells and for sterilising surgical instruments. Beta emitters like technetium-99m are used as tracers because they can be detected outside the body.
放射性根据源的穿透能力和半衰期有许多实际应用。在医学上，γ 射线用于放射治疗以杀死癌细胞，也用于消毒手术器械。锝-99m 等 β 放射源用作示踪剂，因为其辐射可以在体外检测到。
In industry, alpha sources like americium-241 are used in smoke detectors; beta sources monitor thickness of paper, plastic or metal sheets. Gamma radiography checks welds and cracks in pipelines. Carbon-14 dating determines the age of archaeological specimens up to about 50,000 years.
在工业中，镅-241 等 α 源被用于烟雾探测器；β 源用于监测纸张、塑料或金属板的厚度；γ 射线照相术检查管道焊缝和裂缝。碳-14 定年可测定约五万年内的考古样本年代。
12. Safety and Handling Precautions | 安全与操作预防措施
Because ionising radiation can damage DNA and cause cancer, strict safety measures are necessary when handling radioactive sources. Always use sources with the lowest activity possible and keep exposure time to a minimum. Handle sources with tongs and keep them at arm’s length, with the source pointing away from the body.
由于电离辐射会损伤 DNA 并可能导致癌症，处理放射源时必须采取严格的安全措施。始终使用活度尽可能低的源，并尽量减少暴露时间。用镊子夹取源，保持一臂距离，源的方向要背离身体。
Store sources in lead-lined containers when not in use. Never eat, drink or apply cosmetics near radioactive materials. For emergency situations, wear protective clothing and use film badges to monitor cumulative radiation dose.
不使用时将源存放在衬铅的容器中。切勿在放射源附近饮食或涂抹化妆品。在紧急情况下，穿戴防护服并使用胶片剂量计监测累积辐射剂量。
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