📚 Particles, Radiation and Radioactivity | 粒子、辐射与放射性
This article covers the essential ideas of particle physics and radioactivity for AQA A-Level Physics. You will learn about the structure of the atom, the nature of fundamental particles, the interactions between them, and the laws that govern radioactive decay.
本文涵盖AQA A-Level物理中粒子物理和放射性的核心概念。你将了解原子的结构、基本粒子的性质、它们之间的相互作用，以及支配放射性衰变的规律。
1. The Atom and Its Constituents | 原子及其构成
An atom consists of a small, dense nucleus surrounded by orbiting electrons. The nucleus itself contains protons and neutrons, which are collectively called nucleons.
原子由一个微小而致密的原子核以及围绕它运动的电子组成。原子核本身包含质子和中子，统称为核子。
- Proton: charge +e, rest mass 1.673 × 10⁻²⁷ kg
- 质子：电荷 +e，静止质量 1.673 × 10⁻²⁷ kg
- Neutron: charge 0, rest mass 1.675 × 10⁻²⁷ kg
- 中子：电荷 0，静止质量 1.675 × 10⁻²⁷ kg
- Electron: charge −e, rest mass 9.11 × 10⁻³¹ kg
- 电子：电荷 −e，静止质量 9.11 × 10⁻³¹ kg
The atomic number Z is the number of protons, and the mass number A is the total number of protons and neutrons. A nuclide is represented as ᵃₓX, where X is the chemical symbol.
原子序数Z是质子数，质量数A是质子和中子的总数。核素表示为ᵃₓX，其中X是化学符号。
2. Stable and Unstable Nuclei | 稳定与不稳定的原子核
Stability arises from a balance between the attractive strong nuclear force and the repulsive electrostatic force between protons. For small nuclei, stability is achieved when the proton–neutron ratio is close to 1:1.
原子核的稳定性来自强核力（引力）与质子间静电斥力之间的平衡。对于小原子核，当质子数与中子数之比接近1:1时，就达到稳定。
As the nucleus grows larger, more neutrons are needed to provide additional strong force without increasing electrostatic repulsion. When a nucleus has too many or too few neutrons relative to protons, it becomes unstable and tends to decay.
随着原子核增大，需要更多的中子来提供额外的强核力而不增加静电斥力。当原子核的中子相对质子过多或过少时，它变得不稳定并趋于衰变。
N = A − Z
Neutron number N is the difference between mass number and atomic number.
中子数N等于质量数与原子序数之差。
3. Particles, Antiparticles and Photons | 粒子、反粒子与光子
Every particle has an antiparticle with the same mass but opposite charge. When a particle meets its antiparticle, they annihilate, producing energy in the form of photons.
每个粒子都有质量相同但电荷相反的反粒子。当粒子与其反粒子相遇时，它们会发生湮灭，以光子形式释放能量。
E = mc²
Pair production is the reverse process: a high-energy photon can create a particle–antiparticle pair, provided it has enough energy.
电子对产生是逆过程：一个高能光子可以产生一对粒子—反粒子对，前提是能量足够。
- Electron ↔ positron (antielectron)
- 电子 ↔ 正电子（反电子）
- Proton ↔ antiproton
- 质子 ↔ 反质子
- Photon: its own antiparticle
- 光子：它自身的反粒子
4. Particle Interactions | 粒子相互作用
There are four fundamental forces: gravitational, electromagnetic, strong nuclear and weak nuclear. In particle physics, interactions are described using exchange particles (bosons).
自然界存在四种基本作用力：引力、电磁力、强核力和弱核力。在粒子物理中，相互作用通过交换粒子（玻色子）来描述。
| Force | Exchange particle |
| Strong nuclear | Gluon (π meson between nucleons) |
| Electromagnetic | Photon |
| Weak nuclear | W⁺, W⁻, Z⁰ bosons |
| Gravitational | Graviton (not yet observed) |
In A-Level physics, you mainly study two types of hadrons: baryons (three quarks) and mesons (quark–antiquark pairs), plus leptons (such as electrons and neutrinos) which do not feel the strong force.
在A-Level物理中，你主要学习两种强子：重子（三个夸克）和介子（夸克—反夸克对），以及轻子（如电子和中微子），它们不参与强相互作用。
5. Quarks and Antiquarks | 夸克与反夸克
Quarks are fundamental particles that make up hadrons. There are six flavours, but in AQA A-Level you need to know up, down and strange quarks, and their antiquarks.
夸克是组成强子的基本粒子。共有六种味道，但AQA A-Level你需要了解上夸克、下夸克和奇异夸克，以及它们的反夸克。
| Flavour | Charge | Baryon number |
| u | +⅔e | +⅓ |
| d | −⅓e | +⅓ |
| s | −⅓e | +⅓ |
| anti-u | −⅔e | −⅓ |
| anti-d | +⅓e | −⅓ |
| anti-s | +⅓e | −⅓ |
Protons are uud, neutrons are udd. The decay of a neutron involves a down quark changing to an up quark via the weak interaction, emitting a W⁻ boson that decays into an electron and an antineutrino.
质子由uud组成，中子由udd组成。中子衰变涉及下夸克通过弱相互作用变为上夸克，发射W⁻玻色子，再衰变为电子和反中微子。
6. Conservation Laws | 守恒定律
In every particle interaction or radioactive decay, certain quantities must be conserved: charge, baryon number, lepton number and energy–momentum. Strangeness is conserved in strong interactions but not in weak interactions.
在每个粒子相互作用或放射性衰变中，某些量必须守恒：电荷、重子数、轻子数和能量—动量。奇异数在强相互作用中守恒，但在弱相互作用中不守恒。
- Charge: total electric charge before = after
- 电荷：反应前后总电荷相等
- Baryon number: total baryon number is constant
- 重子数：总重子数保持不变
- Lepton number: separate conservation for electron, muon and tau families
- 轻子数：电子、μ子和τ子家族分别守恒
n → p + e⁻ + ν̄ₑ
This beta-minus decay satisfies all conservation laws: charge (0 → +1−1), baryon number (1 → 1), lepton number (electron family 0 → 1−1).
这个β⁻衰变满足所有守恒定律：电荷（0 → +1−1），重子数（1 → 1），轻子数（电子家族 0 → 1−1）。
7. Radioactivity: Alpha, Beta and Gamma | 放射性：α、β与γ
Unstable nuclei emit radiation to become more stable. There are three main types of radiation, each with different penetration and ionising power.
不稳定的原子核通过发射辐射而变得更稳定。主要有三种辐射类型，各有不同的穿透能力和电离能力。
| Type | Nature | Range in air | Stopped by |
| Alpha (α) | Helium nucleus ⁴₂He | ~5 cm | Paper / skin |
| Beta (β⁻) | Fast electron ±₋₁e | ~1 m | Few mm aluminium |
| Gamma (γ) | High-energy photon | Infinite (intensity decreases) | Several cm lead / concrete |
Alpha particles are strongly ionising because of their large charge and slow speed. Beta particles are moderately ionising. Gamma radiation is weakly ionising but very penetrating.
α粒子因为电荷大、速度慢而具有很强的电离能力。β粒子具有中等电离能力。γ辐射电离能力弱，但穿透力很强。
8. Nuclear Equations | 核反应方程式
When writing nuclear equations, the total mass number and total charge must balance on both sides. Use the nuclide notation ᵃₓX for each particle.
写核反应方程式时，两侧的总质量数和总电荷必须平衡。每个粒子使用核素表示法ᵃₓX。
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
Alpha decay: mass number decreases by 4, atomic number decreases by 2.
α衰变：质量数减少4，原子序数减少2。
¹⁴₆C → ¹⁴₇N + ₀₋₁e + ν̄ₑ
Beta-minus decay: a neutron becomes a proton; mass number stays the same, atomic number increases by 1.
β⁻衰变：中子变为质子；质量数不变，原子序数增加1。
9. Half-Life and Decay Curves | 半衰期与衰变曲线
The half-life T₁/₂ is the time taken for half of the radioactive nuclei in a sample to decay. It is a constant for a given isotope and does not depend on temperature, pressure or chemical state.
半衰期T₁/₂是指样品中一半放射性核衰变所需的时间。对于特定同位素它是一个常数，不随温度、压力或化学状态而改变。
N = N₀ (½)t/T₁/₂
Equivalently, using the decay constant λ:
等价地，使用衰变常数λ：
N = N₀ e^(−λt) and T₁/₂ = ln2 / λ
The activity A of a sample is the rate of decay, measured in becquerels (Bq).
样品的活度A是衰变率，单位为贝克勒尔（Bq）。
A = λN = A₀ e^(−λt)
A decay curve is exponential, and after each half-life the activity falls to half of its previous value.
衰变曲线是指数式的，每经过一个半衰期，活度下降到原值的一半。
10. Ionising Radiation and Applications | 电离辐射与应用
Ionising radiation can damage cells by knocking electrons out of atoms, causing mutations or cancer. However, it is also used in medicine and industry.
电离辐射通过将电子从原子中击出而损伤细胞，可能导致突变或癌症。然而，它也用于医学和工业。
- Medical tracers: iodine-131 and technetium-99m emit gamma rays that can be detected outside the body.
- 医用示踪剂：碘-131和锝-99m发射γ射线，可在体外被探测到。
- Radiotherapy: cobalt-60 gamma radiation is used to destroy cancerous tumours.
- 放射治疗：钴-60的γ辐射用于摧毁癌性肿瘤。
- Carbon dating: the ratio of carbon-14 to carbon-12 determines the age of organic materials.
- 碳定年：碳-14与碳-12的比例可用于确定有机材料年代。
- Smoke detectors: americium-241 emits alpha particles which ionise the air; smoke reduces the current and triggers an alarm.
- 烟雾探测器：镅-241发射α粒子使空气电离；烟雾降低电流从而触发警报。
When working with radioactive sources, safety measures include using tongs, limiting exposure time, and shielding with appropriate materials.
使用放射源时，安全措施包括使用钳子、限制暴露时间，并用适当的材料进行屏蔽。
Published by TutorHao | Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导