📚 The Structure of Matter | 物质的结构
Understanding the structure of matter is one of the central quests of physics, leading from the discovery of the atomic nucleus to the intricate tapestry of quarks and leptons that make up the universe. The Standard Model of particle physics provides our most complete description, classifying fundamental particles and the forces through which they interact.
理解物质的结构是物理学的核心探索之一，从原子核的发现一直延伸到构成宇宙的夸克与轻子交织的精妙图景。粒子物理的标准模型提供了我们目前最完备的描述，对基本粒子及其相互作用力进行了分类。
1. The Nuclear Atom: Rutherford's Discovery | 核式原子：卢瑟福的发现
In 1909, Hans Geiger and Ernest Marsden, under the direction of Ernest Rutherford, fired alpha particles at a thin gold foil. Most passed straight through, but a tiny fraction were deflected at large angles, some even bouncing straight back.
1909年，汉斯·盖革和欧内斯特·马斯登在欧内斯特·卢瑟福的指导下，用α粒子轰击薄金箔。大多数粒子径直穿过，但有极少数被大角度偏转，有些甚至直接反弹回来。
Rutherford interpreted these results as evidence for a small, dense, positively charged nucleus at the centre of the atom, with electrons orbiting at relatively large distances. This overturned the earlier 'plum pudding' model.
卢瑟福将这些结果解释为原子中心存在一个微小、致密、带正电荷的原子核，电子则在相对遥远的距离上绕行。这推翻了先前的“葡萄干布丁”模型。
The nuclear model revealed that the atom is mostly empty space, and that the positive charge and nearly all the mass are concentrated in the nucleus, whose radius is about 10⁻¹⁵ m, compared to the atomic radius of about 10⁻¹⁰ m.
核式模型揭示了原子内部绝大部分是虚空，正电荷与几乎全部质量都集中在原子核内，核半径约为10⁻¹⁵ 米，而原子半径约为10⁻¹⁰ 米。
2. Nucleons and Isotopes | 核子与同位素
y neutral. Both have a mass roughly equal to one atomic mass unit (1 u ≈ 1.66 × 10⁻²⁷ kg).
原子核由两类核子组成：带一个正基本电荷（+1 e）的质子，以及电中性的中子。两者的质量约等于一个原子质量单位（1 u ≈ 1.66 × 10⁻²⁷ 千克）。
e A = Z + N), giving them identical chemical properties but different nuclear stabilities.
质子数决定了原子序数 Z 和化学元素；核子总数为质量数 A。一种元素的同位素具有相同的 Z，但中子数 N 不同（A = Z + N），因此它们化学性质相同，但核稳定性不同。
For example, carbon-12 has 6 protons and 6 neutrons (¹²₆C), while radioactive carbon-14 has 6 protons and 8 neutrons (¹⁴₆C). Such isotopic variations are key to understanding nuclear reactions and radioactivity.
例如，碳-12 有 6 个质子和 6 个中子（¹²₆C），而放射性碳-14 有 6 个质子和 8 个中子（
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