📚 Radiation from Radioactive Substances | 放射性物质的辐射
Radioactive substances are materials that spontaneously emit radiation due to unstable atomic nuclei. This phenomenon, known as radioactivity, involves the release of particles and electromagnetic waves that carry energy away from the nucleus. Understanding the types and properties of these radiations is fundamental to nuclear physics and has widespread applications in medicine, industry, and energy production.
放射性物质是指由于原子核不稳定而自发地发出辐射的物质。这种现象被称为放射性，涉及粒子和电磁波的释放，它们从原子核带走能量。理解这些辐射的类型和性质是核物理学的基础，并在医学、工业和能源生产中有广泛应用。
1. Introduction to Radioactivity | 放射性的简介
The nucleus of an atom contains protons and neutrons, held together by the strong nuclear force. When the nucleus has an imbalance of protons and neutrons or excess energy, it becomes unstable and decays, emitting radiation. This process is entirely random and spontaneous, unaffected by external conditions such as temperature and pressure.
原子核包含质子和中子，由强核力结合在一起。当原子核内质子与中子失衡或能量过剩时，它将变得不稳定并发生衰变，发射出辐射。这个过程是完全随机的、自发的，不受温度、压力等外部条件的影响。
2. Types of Nuclear Radiation | 核辐射的类型
Radiation from radioactive substances was first classified by Ernest Rutherford into three distinct types: alpha (α), beta (β) and gamma (γ) rays. They differ in their nature, charge, mass, penetrating power and ionising ability. Alpha particles are helium nuclei, beta particles are fast-moving electrons (or positrons), and gamma rays are high-energy electromagnetic photons.
放射性物质发出的辐射最初由卢瑟福分为三种不同的类型：α射线、β射线和γ射线。它们在本质、电荷、质量、穿透能力和电离能力上各不相同。α粒子是氦核，β粒子是快速运动的电子（或正电子），γ射线是高能电磁光子。
3. Alpha Particles: Nature and Characteristics | α粒子：本质和特性
An alpha particle consists of two protons and two neutrons, identical to a helium-4 nucleus. It is represented as ⁴₂He. Alpha particles have a relatively large mass (about 4 u) and carry a double positive charge (+2e). They are emitted by heavy radioactive nuclei, for example in the decay of uranium-238:
α粒子由两个质子和两个中子组成，与氦-4核相同，符号为⁴₂He。α粒子具有较大的质量（约4 u）并带双正电荷（+2e）。它们由重放射性核素发射，例如铀-238的衰变：
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
Due to their size and charge, alpha particles interact strongly with matter, losing energy rapidly. They can travel only a few centimetres in air and can be stopped by a sheet of paper or the outer layer of skin. However, if ingested or inhaled, they cause severe biological damage because of their intense ionisation.
由于体积和电荷，α粒子与物质相互作用强烈，迅速损失能量。它们在空气中只能穿行几厘米，可以被一张纸或皮肤外层阻挡。然而，如果被摄入或吸入，它们因强烈的电离作用而造成严重的生物损伤。
4. Beta Particles: Electrons from the Nucleus | β粒子：来自原子核的电子
Beta radiation consists of high-speed electrons (β⁻) or positrons (β⁺). In β⁻ decay, a neutron in the nucleus transforms into a proton, emitting an electron and an antineutrino: n → p + e⁻ + ν̅ₑ. The electron is the beta particle, symbolised as ⁰₋₁e. In β⁺ decay, a proton converts to a neutron, releasing a positron and a neutrino: p → n + e⁺ + νₑ.
β辐射由高速电子（β⁻）或正电子（β⁺）组成。在β⁻衰变中，核内的一个中子转变成质子，放出一个电子和一个反中微子：n → p + e⁻ + ν̅ₑ。电子就是β粒子，符号为⁰₋₁e。在β⁺衰变中，质子转变为中子，释放一个正电子和一个中微子：p → n + e⁺ + νₑ。
Beta particles have much smaller mass than alpha particles and a single charge (-e or +e), so they travel faster and are less ionising. They can penetrate several millimetres of aluminium and several metres of air before being absorbed.
β粒子的质量远小于α粒子，带单个电荷（-e 或 +e），因此它们的运动速度更快，电离能力较弱。它们能穿透几毫米的铝和几米的空气后才被吸收。
5. Gamma Rays: High-Energy Photons | γ射线：高能光子
Gamma rays are electromagnetic radiation of very high frequency and energy, with no mass and no charge. They are usually emitted after alpha or beta decay when the daughter nucleus is left in an excited state. Gamma emission does not change the mass number or atomic number and is represented as ⁰₀γ.
γ射线是频率极高、能量极大的电磁辐射，没有质量和电荷。它们通常在α或β衰变后，子核处于激发态时释放。γ发射不改变质量数或原子序数，符号为⁰₀γ。
Gamma photons are highly penetrating, requiring several centimetres of lead or thick concrete to reduce their intensity significantly. Although weakly ionising, they can pass through the human body and cause deep tissue damage, which is why shielding is critical when handling gamma sources.
γ光子穿透能力极强，需要几厘米厚的铅或厚混凝土才能显著减弱其强度。尽管电离能力弱，但它们能穿透人体并造成深层组织损伤，因此在处理γ源时必须做好屏蔽。
6. Penetrating Power and Range | 穿透能力和射程
The penetrating power of nuclear radiation depends on its type. Alpha radiation is easily stopped because of its large mass and charge, beta radiation has a moderate range, and gamma rays can travel long distances with little attenuation. The following table summarises a typical comparison:
核辐射的穿透能力取决于其类型。α辐射因其质量和电荷大而极易被阻挡，β辐射具有中等射程，而γ射线能在衰减很小的情况下传播很远。下表总结了典型的比较：
| Type | Symbol | Charge | Typical Penetration | Stopped by |
|---|---|---|---|---|
| Alpha | ⁴₂He | +2e | few cm of air | sheet of paper, skin |
| Beta | ⁰₋₁e | -1e | a few mm to several m of air | few mm of aluminium |
| Gamma | ⁰₀γ | 0 | many metres of air | several cm of lead or thick concrete |
Alpha particles lose all their energy in a very short distance, making their range in air typically 2-8 cm. Beta particles can travel up to a few metres in air, but are readily absorbed by a few millimetres of aluminium. Gamma rays, on the other hand, have no definite range and are exponentially attenuated, requiring dense materials for effective shielding.
α粒子在极短距离内就损失全部能量，它们空气中的射程通常为2-8 cm。β粒子可在空气中穿行数米，但很容易被几毫米的铝吸收。而γ射线没有确定的射程，呈指数衰减，需要高密度材料才能有效屏蔽。
7. Ionising Ability | 电离能力
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