📚 AQA A-Level Physics: Particles and Radiation | AQA A-Level物理：粒子与辐射
In AQA A-Level Physics, the Particles and Radiation topic underpins nuclear physics, quantum phenomena and the standard model of matter. This article reviews the key facts, equations and exam techniques you need to master this unit.
在AQA A-Level物理中，粒子与辐射是核物理、量子现象和物质标准模型的基础。本文梳理关键事实、公式和考试技巧，帮助你掌握本单元。
1. Constituents of the Atom | 原子的组成
An atom consists of a dense positive nucleus containing protons and neutrons, surrounded by orbiting electrons. The proton number Z defines the element, while the nucleon number A gives the total number of protons plus neutrons.
原子由一个致密的正电原子核以及绕核运动的电子组成，原子核内含质子和中子。质子数Z决定元素种类，核子数A是质子数与中子数之和。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have identical chemical properties but different physical properties such as mass and nuclear stability.
同位素是指质子数相同而中子数不同的同种元素原子。它们化学性质相同，但质量和核稳定性等物理性质不同。
For a proton, specific charge = (1.60 × 10⁻¹⁹ C) / (1.67 × 10⁻²⁷ kg) ≈ 9.58 × 10⁷ C kg⁻¹.
比荷是电荷与质量的比值，通常以 C kg⁻¹ 为单位。质子的比荷 = (1.60 × 10⁻¹⁹ C) / (1.67 × 10⁻²⁷ kg) ≈ 9.58 × 10⁷ C kg⁻¹。
2. Stable and Unstable Nuclei | 稳定与不稳定的原子核
The strong nuclear force holds nucleons together. It is attractive up to about 3 fm, repulsive below about 0.5 fm, and acts between all nucleons independent of electric charge.
强核力将核子束缚在一起。它在约3 fm范围内表现为引力，低于约0.5 fm时表现为斥力，并且对所有核子起作用，与电荷无关。
Unstable nuclei emit alpha, beta or gamma radiation to become more stable. Alpha decay reduces A by 4 and Z by 2; beta-minus decay increases Z by 1 with A unchanged.
不稳定原子核通过发射α、β或γ辐射趋向稳定。α衰变使A减少4、Z减少2；β⁻衰变使Z增加1，A不变。
Gamma radiation often follows alpha or beta decay because the daughter nucleus is left in an excited state. Gamma rays carry no charge and have no rest mass.
γ辐射通常在α或β衰变后发射，因为子核处于激发态。γ射线不带电荷，也没有静质量。
3. Particles and Antiparticles | 粒子与反粒子
Every particle has a corresponding antiparticle with the same mass and rest energy but opposite charge and quantum numbers. For example, the positron is the antiparticle of the electron.
每种粒子都有对应的反粒子，其质量和静能相同，但电荷和量子数相反。例如，正电子是电子的反粒子。
Annihilation occurs when a particle meets its antiparticle, converting their total mass-energy into two photons. Pair production is the reverse process where a photon creates a particle-antiparticle pair.
湮灭是指粒子与反粒子相遇，把它们的总质能转化为两个光子。电子对产生是逆过程，即一个光子产生一对粒子-反粒子。
of the particle and antiparticle. For an electron-positron pair this is 2mₑc² ≈ 1.02 MeV.
要发生电子对产生，光子能量至少必须等于粒子和反粒子的总静能。对电子-正电子对而言，这约为 2mₑc² ≈ 1.02 MeV。
4. Forces and Exchange Particles | 力与交换粒子
In the standard model, forces are explained by exchange particles called gauge bosons. The electromagnetic force is mediated by virtual photons, and the weak nuclear force by W⁺, W⁻ and Z⁰ bosons.
在标准模型中，力由称为规范玻色子的交换粒子解释。电磁力由虚光子传递，弱核力由 W⁺、W⁻ 和 Z⁰ 玻色子传递。
Exchange particles are virtual, meaning they exist for a very short time and cannot be directly observed. Their range is limited by the uncertainty principle.
交换粒子是虚粒子，意味着它们存在时间极短且无法直接观测。它们的作用范围受不确定原理限制。
The strong force is carried by gluons, but AQA mainly requires you to understand its role in holding quarks together inside hadrons. Gravitational exchange particles, gravitons, are not needed at this level.
强力由胶子传递，但AQA主要要求你理解它在强子内部束缚夸克的作用。引力交换粒子（引力子）在本阶段不作要求。
5. The Photon Model | 光子模型
energy of a photon is given by E = hf, where h = 6.63 × 10⁻³⁴ J s and f is the frequency.
电磁波以称为光子的分立能量包形式到达。光子能量由 E = hf 给出，其中 h = 6.63 × 10⁻³⁴ J s，f 是频率。
E = hf = hc / λ
can also be written E = hc / λ. A photon with wavelength 550 nm has energy about 2.25 eV.
因为 c = fλ，光子能量也可写作 E = hc / λ。波长为550 nm的光子能量约为2.25 eV。
P / E. This allows conversion between macroscopic power and microscopic photon behaviour.
对于功率为P、光子能量为E的光束，每秒发射的光子数为 N = P / E。这实现了宏观功率与微观光子行为之间的转换。
6. The Electromagnetic Spectrum | 电磁波谱
The electromagnetic spectrum orders waves by frequency and wavelength, from radio waves through microwaves, infrared, visible light, ultraviolet, X-rays to gamma rays. Photon energy increases with frequency.
电磁波谱按频率和波长排序，从无线电波、微波、红外、可见光、紫外、X射线到γ射线。光子能量随频率增加而增大。
AQA candidates need to know the approximate ranges, especially the visible spectrum from about 400 nm to 700 nm and the fact that gamma rays originate from nuclear transitions.
AQA考生需要知道大致范围，特别是可见光谱约400 nm至700 nm，以及γ射线来源于原子核能级跃迁。
Ultraviolet radiation is produced when electrons move between high energy levels in atoms, whereas X-rays are produced by rapid deceleration of high-speed electrons or by inner-shell electron transitions.
紫外辐射产生于原子中电子在高能级之间跃迁，而X射线则通过高速电子快速减速或内壳层电子跃迁产生。
7. Wave-Particle Duality | 波粒二象性
his is significant for tiny objects such as electrons, but negligible for macroscopic objects.
物质可以表现出波动性，德布罗意波长 λ = h / p = h / (mv)。这对电子等微小物体尤为重要，对宏观物体可忽略不计。
λ = h / p = h / (mv)
Electron diffraction through graphite demonstrates wave-like behaviour. As the accelerating voltage increases, the electron wavelength decreases and the diffraction rings become smaller.
电子穿过石墨的衍射证明了波动性。随着加速电压增大，电子波长减小，衍射环变小。
then substitute into λ = h / mv. Remember to convert electron volts into joules if needed.
要根据加速电压V计算电子速度，可用 eV = ½mv²，然后代入 λ = h / mv。如需转换，记得把电子伏特换算为焦耳。
8. Energy Levels and Spectra | 能级与光谱
Electrons in atoms occupy discrete energy levels. They can move to higher levels by absorbing a photon with energy exactly equal to the energy difference, or drop down by emitting such a photon.
原子中的电子占据分立的能级。它们可以通过吸收能量恰好等于能级差的光子跃迁到较高能级，或通过发射这样的光子向下跃迁。
Excitation is the promotion of an electron to a higher level; ionisation is the removal of the electron entirely. The ionisation energy of hydrogen from the ground state is 13.6 eV.
激发是指电子被提升到较高能级；电离是指电子被完全移出。氢原子从基态电离所需的电离能是13.6 eV。
Fluorescent tubes use excitation and de-excitation. Electrons collide with mercury atoms, exciting them; when they drop back down, ultraviolet photons are emitted, which are then absorbed by a phosphor coating and re-emitted as visible light.
荧光灯利用激发和退激发过程。电子与汞原子碰撞使其激发；当汞原子跃迁回低能级时发射紫外光子，紫外光子被荧光粉涂层吸收并重新发射为可见光。
9. Particle Interactions | 粒子相互作用
Interactions can be classified as strong, weak, electromagnetic or gravitational. The weak interaction is responsible for beta decay, changing a down quark into an up quark or vice versa.
相互作用可分为强、弱、电磁和引力相互作用。弱相互作用负责β衰变，使下夸克变为上夸克或反之。
Particle collisions obey conservation of energy, momentum, charge, baryon number and lepton number. These rules decide whether a reaction is possible.
粒子碰撞遵守能量、动量、电荷、重子数和轻子数守恒。这些规则决定一个反应是否可能。
In beta-minus decay, a neutron changes into a proton, an electron and an anti-electron neutrino. In beta-plus decay, a proton changes into a neutron, a positron and an electron neutrino.
在β⁻衰变中，中子转变为质子、电子和反电子中微子。在β⁺衰变中，质子转变为中子、正电子和电子中微子。
10. Conservation Laws | 守恒定律
Baryon number is +1 for baryons, −1 for antibaryons and 0 for leptons and mesons. Lepton number is conserved separately for electron, muon and tau families in AQA treatments.
重子数对于重子为+1，反重子为−1，轻子和介子为0。在AQA处理中，电子、μ子和τ族的轻子数分别守恒。
Strangeness is conserved in strong and electromagnetic interactions but not in weak interactions. For example, the strange quark has strangeness −1, and the antistrange quark has strangeness +1.
奇异数在强和电磁相互作用中守恒，但在弱相互作用中不守恒。例如，奇异夸克的奇异数为−1，反奇异夸克的奇异数为+1。
When checking a particle equation, write the relevant quantum numbers on both sides. If any conservation law is violated, the interaction is forbidden.
检查粒子方程时，把相关量子数写在方程两侧。如果违反任何守恒定律，该相互作用就不可能发生。
11. The Standard Model and Quarks | 标准模型与夸克
Hadrons are particles made of quarks. Baryons contain three quarks, while mesons contain a quark and an antiquark. Protons are uud; neutrons
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