📚 AQA A-Level Physics: Particles and Radiation | AQA A Level 物理：粒子与辐射
Welcome to this AQA A-Level Physics revision guide on particles and radiation. This topic lays the foundation for understanding the quantum world, from the structure of the atom to the fundamental particles that make up matter and the interactions between them. We will cover key definitions, equations, and exam techniques required by the AQA specification.
欢迎阅读本篇 AQA A Level 物理粒子与辐射复习指南。本主题为理解量子世界奠定基础，涵盖原子结构、构成物质的基本粒子以及它们之间的相互作用。我们将讲解 AQA 考纲要求的关键定义、公式和解题技巧。
1. Atomic Structure and the Nuclear Model | 原子结构与核模型
Atoms consist of a small, dense, positively charged nucleus surrounded by electrons in discrete energy levels. The nucleus contains protons and neutrons, collectively called nucleons. The proton number (atomic number) Z gives the element's identity, while the nucleon number (mass number) A gives the total number of nucleons.
原子由一个微小、致密、带正电的原子核以及处于分立能级上的电子组成。原子核含有质子和中子，统称为核子。质子数（原子序数）Z 决定了元素的种类，而核子数（质量数）A 给出核子的总数。
Rutherford's alpha scattering experiment provided the evidence for the nuclear model. Most alpha particles passed straight through the gold foil, but a small fraction were deflected through large angles, showing that mass and positive charge are concentrated in a tiny central nucleus.
卢瑟福的 α 散射实验为核模型提供了证据。大多数 α 粒子直接穿过金箔，但有少量发生大角度偏转，表明质量和正电荷集中在极小的中心核上。
| Particle | Relative charge | Relative mass |
|---|---|---|
| proton | +1 | 1 |
| neutron | 0 | 1 |
| electron | -1 | 1/1840 |
中文：质子相对电荷 +1、相对质量 1；中子相对电荷 0、相对质量 1；电子相对电荷 -1、相对质量约 1/1840。
2. Isotopes and Specific Charge | 同位素与比荷
Isotopes are atoms of the same element with the same proton number Z but different neutron numbers N. They have identical chemical properties but different physical properties such as mass and stability.
同位素是质子数 Z 相同但中子数 N 不同的同一元素原子。它们化学性质相同，但质量和稳定性等物理性质不同。
calculating specific charge of a nucleus, only the proton charge is considered, not the neutrons.
比荷定义为电荷与质量之比 Q/m，单位为 C kg⁻¹。例如，质子的比荷为 e/mₚ = 1.60 × 10⁻¹⁹ C ÷ 1.67 × 10⁻²⁷ kg ≈ 9.58 × 10⁷ C kg⁻¹。计算原子核的比荷时只考虑质子的电荷，不考虑中子。
specific charge = Q / m
中文：比荷 = Q / m
3. The Strong Nuclear Force and Stability | 强核力与稳定性
The strong nuclear force holds nucleons together, overcoming the electrostatic repulsion between protons. It is a short-range force, effective up to about 3-4 fm, and is attractive at separations around 1-3 fm. Below about 0.5 fm, it becomes repulsive, preventing nucleons from collapsing.
强核力把核子束缚在一起，克服了质子间的静电排斥。它是一种短程力，作用范围约 3-4 fm，且在 1-3 fm 的间距内表现为吸引力。在约 0.5 fm 以下，强核力变为排斥力，防止核子坍缩。
The balance between the repulsive electric force and the attractive strong force explains the stability curve of nuclei. Heavy nuclei need extra neutrons to dilute the proton repulsion and remain stable.
排斥性静电力和吸引性强核力之间的平衡解释了原子核的稳定曲线。重核需要额外的中子来稀释质子排斥以保持稳定。
4. Alpha, Beta and Gamma Radiation | α、β 和 γ 辐射
Unstable nuclei emit radiation to become more stable. Alpha (α) particles are helium nuclei, consisting of two protons and two neutrons. Beta minus (β⁻) decay occurs when a neutron changes into a proton, emitting an electron and an antineutrino. Gamma (γ) radiation is high-energy electromagnetic radiation emitted after alpha or beta decay to release excess energy.
不稳定原子核通过发射辐射变得更稳定。α 粒子是氦核，由两个质子和两个中子组成。β⁻ 衰变发生在中子转变为质子时，发射一个电子和一个反中微子。γ 辐射是 α 或 β 衰变后释放多余能量的高能电磁辐射。
In α decay, A decreases by 4 and Z decreases by 2. In β⁻ decay, A stays constant while Z increases by 1. These changes are shown in balanced nuclear equations.
在 α 衰变中，A 减少 4，Z 减少 2。在 β⁻ 衰变中，A 不变，Z 增加 1。这些变化体现在配平的核方程中。
23892U → 23490Th + 42He
中文：铀-238 的 α 衰变：²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
146C → 147N + e⁻ + ν̄ₑ
中文：碳-14 的 β⁻ 衰变：¹⁴₆C → ¹⁴₇N + e⁻ + 反中微子
5. Photons and the Photoelectric Effect | 光子与光电效应
s the Planck constant and f is frequency. Since c = fλ, this can also be written E = hc/λ.
光和其他电磁辐射由光子组成，光子是能量包。光子的能量由 E = hf 给出，其中 h 是普朗克常量，f 是频率。由于 c = fλ，也可写为 E = hc/λ。
E = hf = hc/λ
中文：E = hf = hc/λ
here φ is the work function. Key evidence includes the threshold frequency, instant emission, and intensity affecting only the number of photoelectrons, not their maximum kinetic energy.
光电效应证明了光的粒子性：频率高于阈值频率的光子能从金属表面打出电子。发射电子的最大动能为 Eₖ max = hf - φ，其中 φ 是逸出功。关键
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