1. 核物理在Edexcel A-Level中的重要性 | Why Nuclear Physics Matters
在Edexcel A-Level物理中，核物理是Unit 4和Unit 5的核心章节，历年考试中约占12%-18%的分数。它不仅考察核结构和放射性衰变的概念理解，还要求掌握定量计算，包括衰变常数、半衰期和结合能。
In Edexcel A-Level Physics, Nuclear Physics is a core topic in Unit 4 and Unit 5, accounting for 12%-18% of exam marks. It tests concept understanding and quantitative skills including decay constants, half-lives, and binding energies.
2. 卢瑟福散射实验 | Rutherford Scattering
卢瑟福的α粒子散射实验是近代物理的里程碑。当α粒子轰击金箔时，大多数径直穿过，约1/8000被大角度反弹。结论：原子核极小且集中了几乎全部质量和正电荷，推翻了汤姆逊模型。考试需能用这一实验证据解释原子的核式结构。
Rutherford's alpha scattering experiment: most particles pass through gold foil, but about 1 in 8000 are reflected at large angles. The conclusion: the nucleus is tiny, positively charged, and contains nearly all the atom's mass. This overturned Thomson's model entirely.
3. 核半径与核密度 | Nuclear Radius and Density
核半径经验公式R = r₀A1/3，其中r₀ ≈ 1.2 fm。这意味着核体积与核子数成正比，所有原子核的密度大致相同——约2.3×10¹⁷ kg/m³。电子衍射实验可精确测量核半径，利用sinθ ≈ 0.61λ/R。
The nuclear radius formula R = r₀A1/3 (r₀ ≈ 1.2 fm) shows nuclear volume is proportional to nucleon number. All nuclei share roughly the same density: about 2.3×10¹⁷ kg/m³. Electron diffraction experiments measure nuclear radius precisely using sinθ ≈ 0.61λ/R.
4. 三种放射性衰变 | Three Types of Radioactive Decay
Alpha衰变：发射氦核，质量数减4，原子序数减2，穿透力最弱但电离最强。Beta衰变（β⁻）：中子→质子+电子+反中微子，质量数不变，原子序数加1。Gamma衰变：激发态跃迁发射高能光子，穿透力最强，常伴随α或β衰变发生。记住穿透力排序：α < β < γ，电离能力则相反。
Alpha decay emits a helium nucleus (mass -4, atomic number -2), weakest penetration but strongest ionisation. Beta-minus decay converts neutron to proton + electron + antineutrino, mass unchanged, atomic number +1. Gamma decay emits high-energy photons from excited nuclei, strongest penetration, often follows α/β decay. Remember: penetration α < β < γ, ionisation is the reverse order.
5. 衰变指数定律与计算 | Exponential Decay Law and Calculations
衰变规律N = N₀e-λt，活度A = λN（单位Bq）。半衰期T₁/₂ = ln2/λ ≈ 0.693/λ。碳-14测年法是典型应用：半衰期5730年，若样本活度为初始的25%，则经历2个半衰期，年代约11460年。考试中此类计算几乎每年必考。
The decay law N = N₀e-λt and activity A = λN (unit: Bq). Half-life T₁/₂ = ln2/λ ≈ 0.693/λ. Carbon-14 dating is a classic application: with half-life 5730 years, if sample activity is 25% of original, 2 half-lives have passed, age ≈ 11,460 years. Expect these calculations every exam year.
6. 质量亏损与结合能 | Mass Defect and Binding Energy
原子核质量小于其组成核子的质量之和——称为质量亏损。利用E = mc²将质量亏损转换为结合能。1 u = 931.5 MeV是考试常用换算。平均结合能越大，核越稳定。铁-56具有最大的平均结合能（~8.8 MeV/核子），这解释了为什么轻核聚变和重核裂变都释放能量。
A nucleus weighs less than the sum of its nucleons — this is the mass defect. Convert it to binding energy via E = mc². The exam constant: 1 u = 931.5 MeV. Higher average binding energy per nucleon = more stable nucleus. Iron-56 has the maximum (~8.8 MeV/nucleon), which explains why both light-nuclei fusion and heavy-nuclei fission release energy.
7. 核裂变与核聚变 | Fission and Fusion
核裂变：铀-235吸收中子后分裂，释放2-3个中子引发链式反应。反应堆中控制棒吸收多余中子，慢化剂减速中子以提高裂变概率。核聚变：两个轻核结合释放巨大能量，需要约10⁸ K高温克服库仑斥力，这是太阳的能源机制。可控聚变的主要挑战是实现净能量增益。
Fission: U-235 absorbs a neutron, splits, and releases 2-3 neutrons for a chain reaction. Reactors use control rods to absorb excess neutrons and moderators to slow neutrons for higher fission probability. Fusion: two light nuclei combine at ~10⁸ K to overcome Coulomb repulsion — the Sun's power source. The key challenge is achieving net energy gain.
8. 高频考点与备考建议 | Exam Tips
放射性衰变计算（指数公式、半衰期与活度）每年必考。结合能曲线分析常以6分论述题出现。核反应堆各组件功能是经典应用题。卢瑟福散射和电子衍射的实验描述题虽分值不高但易失分——务必完整叙述装置、观察和结论。建议重点练习近年真题的Section B计算题。
Decay calculations (exponential formula, half-life, activity) appear every year. Binding energy curve analysis is a common 6-mark extended response. Reactor component functions are classic application questions. Rutherford scattering and electron diffraction experiment descriptions are low-mark but easy to lose — ensure complete accounts of setup, observations, and conclusions. Focus on recent past papers, especially Section B calculations.
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