How Scientists Work: Inside Sub-atomic Particles | 科学家如何探索亚原子粒子内部

📚 How Scientists Work: Inside Sub-atomic Particles | 科学家如何探索亚原子粒子内部

Everything around you is made of atoms, but atoms are not the smallest building blocks. This article explains how scientists worked out the structure inside the atom and discovered even smaller sub-atomic particles, from protons and neutrons to quarks.

你身边的一切物质都由原子组成，但原子并不是最小的”积木”。本文将解释科学家如何逐步弄清原子内部结构，并发现更小的亚原子粒子——从质子、中子到夸克。

1. From Atoms to Sub-atomic Particles | 从原子到亚原子粒子

Atoms were once thought to be indivisible, but experiments showed that each atom contains a tiny, dense nucleus surrounded by electrons. The word “sub-atomic” means “smaller than an atom”, so protons, neutrons and electrons are all sub-atomic particles.

原子曾被认为是不可再分的，但实验表明每个原子都含有一个微小致密的原子核，周围有电子。”sub-atomic” 意思是 “比原子更小”，因此质子、中子和电子都属于亚原子粒子。

In chemistry, the arrangement of electrons is especially important because it controls how elements react and bond. However, physicists can look even deeper, inside protons and neutrons, to find quarks.

在化学中，电子的排布尤其重要，因为它控制元素如何反应和成键。然而物理学家还可以看得更深——进入质子和中子内部，发现夸克。

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2. Dalton’s Atomic Model | 道尔顿的原子模型

John Dalton’s early 19th-century model described atoms as hard, solid spheres that could not be split. This was a useful starting point, but it could not explain static electricity or the behaviour of gases in discharge tubes.

约翰·道尔顿在 19 世纪初提出的模型把原子描述为不可分裂的坚硬实心球体。这是一个有用的起点，但无法解释静电或气体在放电管中的行为。

Scientific models are not fixed facts. When new evidence does not fit the model, scientists change the model. Dalton’s sphere was gradually replaced as experiments revealed charged particles inside the atom.

科学模型并不是固定不变的事实。当新证据与模型不符时，科学家就会修改模型。道尔顿的球体模型随着实验揭示原子内部带电粒子而被逐渐取代。

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3. Thomson Discovers the Electron | 汤姆孙发现电子

J. J. Thomson passed electricity through a gas at low pressure and produced cathode rays. He showed that these rays were streams of tiny, negatively charged particles, now called electrons.

J. J. 汤姆孙让电流通过低压气体，产生了阴极射线。他证明这些射线是微小的带负电粒子流，也就是现在所说的电子。

Thomson proposed the “plum pudding model”: a ball of positive charge with negative electrons scattered inside, like fruit in a pudding. This model helped explain why atoms are neutral overall.

汤姆孙提出了 “葡萄干布丁模型”：一个带正电的球体，内部散布着负电子，就像布丁里的果粒。这个模型帮助解释了原子整体呈电中性的原因。

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4. Rutherford’s Gold Foil Experiment | 卢瑟福的金箔实验

Ernest Rutherford’s team fired positively charged alpha particles at a very thin gold foil. Most passed straight through, but a few bounced back at large angles.

欧内斯特·卢瑟福的团队用带正电的 α 粒子轰击极薄的金箔。大多数 α 粒子径直穿过，但少数粒子以大角度反弹回来。

Rutherford concluded that the atom is mostly empty space, with a tiny, dense, positively charged nucleus at its centre. The electrons orbit this nucleus, so the “plum pudding model” was abandoned.

卢瑟福得出结论：原子内部大部分是空虚的空间，中心有一个微小、致密、带正电的原子核。电子围绕这个核运动，因此 “葡萄干布丁模型” 被放弃。

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5. The Discovery of Protons and Neutrons | 质子和中子的发现

Rutherford later identified the proton as a positively charged particle inside the nucleus. The number of protons, called the atomic number Z, determines which element an atom is.

卢瑟福后来确认质子是原子核内带正电的粒子。质子的数目称为原子序数 Z，它决定了一个原子属于哪种元素。

James Chadwick discovered the neutron in 1932. Neutrons have no charge and add mass to the nucleus. The mass number A is the total number of protons and neutrons.

詹姆斯·查德威克于 1932 年发现了中子。中子不带电荷，为原子核增加质量。质量数 A 是质子数和中子数的总和。

A = Z + N

Here A is the mass number, Z is the atomic number and N is the number of neutrons.

其中 A 是质量数，Z 是原子序数，N 是中子数。

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6. Inside the Nucleon: Quarks | 走进核子内部：夸克

By the 1960s, experiments showed that protons and neutrons are not fundamental particles. They are made of even smaller particles called quarks.

到 20 世纪 60 年代，实验表明质子和中子并不是基本粒子。它们由更小的粒子——夸克——组成。

A proton contains two up quarks and one down quark, written as uud. A neutron contains one up quark and two down quarks, written as udd.

一个质子含有两个上夸克和一个下夸克，记作 uud。一个中子含有一个上夸克和两个下夸克，记作 udd。

p⁺ = uud ; n⁰ = udd

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