📚 Radioactivity and Nuclear Radiation | 放射性与核辐射
Radioactivity is a natural process by which unstable atomic nuclei lose energy by emitting particles or electromagnetic waves. Understanding radioactivity is essential in IGCSE Science as it explains phenomena ranging from the age of rocks to medical imaging and nuclear power. This article covers the structure of the atom, types of radiation, decay processes, half‑life, uses and safety precautions, directly aligned with the Edexcel IGCSE Science specification.
放射性是不稳定原子核通过发射粒子或电磁波释放能量的自然过程。理解放射性对 IGCSE 科学至关重要，因为它可以解释从岩石年代测定到医学成像和核能的各种现象。本文涵盖原子结构、辐射类型、衰变过程、半衰期、用途及安全措施，与 Edexcel IGCSE 科学大纲直接对应。
1. Structure of the Atom | 原子结构
All matter is composed of atoms. Each atom contains a tiny central nucleus made up of protons and neutrons (collectively called nucleons), surrounded by electrons orbiting in energy levels. The nucleus is positively charged due to the protons, while electrons carry a negative charge. Almost all the mass of an atom is concentrated in the nucleus, but the nucleus occupies only a very small fraction of the atom’s volume.
所有物质都由原子组成。每个原子包含一个由质子和中子（统称为核子）构成的微小中心原子核，电子在能级上绕核运行。由于质子，原子核带正电，而电子带负电。原子几乎所有的质量都集中在原子核上，但原子核仅占据原子体积的极小部分。
The number of protons defines the element and is called the atomic number (Z). The total number of protons and neutrons gives the mass number (A). In a neutral atom, the number of electrons equals the number of protons. Ions are formed when an atom gains or loses electrons.
质子数定义了元素，称为原子序数（Z）。质子与中子总数给出质量数（A）。在中性原子中，电子数等于质子数。当原子得到或失去电子时就形成离子。
2. Isotopes and Nuclide Notation | 同位素与核素符号
Isotopes are atoms of the same element (same atomic number) but with different mass numbers due to a different number of neutrons. For example, carbon‑12 (¹²₆C) and carbon‑14 (¹⁴₆C) are two isotopes of carbon. Nuclide notation is written as ᴬᙆX, where A is the mass number, Z is the atomic number, and X is the chemical symbol.
同位素是同一种元素（原子序数相同）但中子数不同从而质量数不同的原子。例如，碳‑12（¹²₆C）和碳‑14（¹⁴₆C）是碳的两种同位素。核素符号写作 ᴬᙆX，其中 A 是质量数，Z 是原子序数，X 是化学符号。
Some isotopes are stable, while others are unstable (radioisotopes) and decay by emitting radiation to become more stable. The instability arises from an imbalance in the proton‑to‑neutron ratio or excess energy in the nucleus.
一些同位素是稳定的，而另一些是不稳定的（放射性同位素），会通过发射辐射衰变以变得更稳定。这种不稳定性源于核内质子‑中子比失衡或过剩的能量。
3. Introduction to Radioactivity | 放射性简介
Radioactivity is the spontaneous disintegration of an unstable nucleus, resulting in the emission of ionising radiation. This process is random and is not affected by physical conditions such as temperature or pressure. The original unstable nucleus is called the parent nuclide, which transforms into a daughter nuclide – often of a different element – together with the release of a radiation particle or photon.
放射性是不稳定原子核的自发衰变，释放出电离辐射。这一过程是随机的，不受温度或压强等物理条件的影响。原始的不稳定核称为母体核素，它转变成子体核素——往往是不同元素的核——同时释放辐射粒子或光子。
There are three main types of nuclear radiation: alpha (α), beta (β) and gamma (γ). Their discovery was closely tied to experiments with magnetic and electric fields, and each has distinct properties in terms of charge, mass, penetration and ionising ability.
核辐射主要有三种类型：α（阿尔法）、β（贝塔）和 γ（伽马）。它们的发现与磁场和电场实验密切相关，每种辐射在电荷、质量、穿透力和电离能力方面都有独特的性质。
4. Types of Nuclear Radiation | 核辐射的类型
An alpha particle is identical to a helium nucleus, consisting of two protons and two neutrons. It is represented as ⁴₂He or α. Beta radiation is a fast‑moving electron ejected from the nucleus when a neutron transforms into a proton. It is written as ⁰₋₁e or β⁻. Gamma radiation is electromagnetic radiation of very short wavelength and high frequency, with no mass or charge.
α 粒子与氦原子核相同，由两个质子和两个中子组成。它表示为 ⁴₂He 或 α。β 辐射是原子核内一个中子转变为质子时射出的高速电子。写作 ⁰₋₁e 或 β⁻。γ 辐射是波长极短、频率极高的电磁辐射，没有质量也不带电荷。
Occasionally, a positron (β⁺) may be emitted when a proton turns into a neutron. This is antimatter and is less common in IGCSE. We focus on the three main types.
有时，当质子转变为中子时，会发射正电子（β⁺）。这是反物质，在 IGCSE 中较少见。我们重点关注这三种主要类型。
5. Properties of Alpha, Beta and Gamma | α、β、γ的性质
The properties of each radiation can be summarised in terms of their nature, charge, penetrating power, ionising ability and behaviour in electric and magnetic fields. A comparison table is very useful for revision.
每种辐射的性质可以从其本质、电荷、穿透能力、电离能力以及电场和磁场中的行为进行概括。对比表格对复习非常有用。
| Property | Alpha (α) | Beta (β⁻) | Gamma (γ) |
| Nature | Helium nucleus (2p+2n) | Fast electron | Electromagnetic wave |
| Charge | +2 (positive) | −1 (negative) | 0 (none) |
| Penetration | Stopped by paper / few cm of air | Stopped by a few mm of aluminium | Reduced by thick lead or concrete |
| Ionising power | Very high | Medium | Low |
| Speed | ~ 5% of light speed | Up to ~ 99% of light speed | Speed of light |
Alpha particles are highly ionising because their large mass and double positive charge allow them to pull electrons from atoms over a short distance. Beta particles ionise less densely, while gamma photons are weakly ionising but highly penetrating, making them hazardous even at a distance.
α 粒子电离能力极强，因为其质量大且带双正电荷，能在短距离内拉出原子的电子。β 粒子电离能力较弱，而 γ 光子电离作用很弱但穿透力极强，即使在远处也有危害。
6. Deflection in Electric and Magnetic Fields | 电场与磁场中的偏转
Charged particles are deflected by electric and magnetic fields, whereas neutral gamma rays are not. In an electric field, alpha particles (positive) are attracted towards the negative plate, and beta particles (negative) are attracted towards the positive plate. The deflection of beta is much greater than that of alpha because beta particles have a much smaller mass.
带电粒子会被电场和磁场偏转，而中性 γ 射线则不会。在电场中，α 粒子（正电）被吸引到负极板，β 粒子（负电）被吸引到正极板。β 的偏转比 α 大得多，因为 β 粒子的质量小得多。
In a magnetic field, the direction of deflection is given by Fleming’s left‑hand rule for moving charges. Alpha and beta are deflected in opposite directions, while gamma continues straight. The amount of deflection is greater for particles with higher charge‑to‑mass ratio, which is why beta curves more sharply.
在磁场中，偏转方向由运动电荷的弗莱明左手定则给出。α 和 β 向相反方向偏转，而 γ 径直前进。偏转量取决于粒子的荷质比，比值越大偏转越大，这就是为什么 β 弯曲更明显。
7. Radioactive Decay Equations | 放射性衰变方程
When writing decay equations, both mass number (A) and atomic number (Z) must balance on both sides. In alpha decay, the parent nucleus loses 4 in mass number and 2 in atomic number, forming a new element. For example, the decay of uranium‑238:
在书写衰变方程时，必须保持两边质量数（A）和原子序数（Z）的平衡。在 α 衰变中，母核质量数减少 4，原子序数减少 2，生成新元素。例如，铀‑238 的衰变：
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
In beta minus decay, a neutron turns into a proton, so the mass number stays constant while the atomic number increases by 1. An example is carbon‑14 decaying to nitrogen‑14:
在 β⁻ 衰变中，一个中子转变为质子，质量数保持不变，而原子序数增加 1。例如碳‑14 衰变成氮‑14：
¹⁴₆C → ¹⁴₇N + ⁰₋₁e + ν̅ₑ
The antineutrino (ν̅ₑ) is often omitted in IGCSE equations, but it is part of the full standard model. Gamma emission usually accompanies alpha or beta decay and does not change the mass or atomic numbers. It is represented by the symbol ⁰₀γ.
反中微子（ν̅ₑ）在 IGCSE 方程中通常省略，但它是完整标准模型的一部分。γ 辐射通常伴随 α 或 β 衰变，不改变质量数或原子序数。它用 ⁰₀γ 表示。
8. Half‑Life | 半衰期
Half‑life (t₁/₂) is the time taken for the radioactivity of a sample to fall to half of its initial value, or equivalently, the time for half the radioactive nuclei in a sample to decay. It is a characteristic property of a particular isotope and is unaffected by external conditions. The decay follows an exponential pattern, but for IGCSE simple calculations you can use successive halving.
半衰期（t₁/₂）是指样品放射性强度降至初始值一半所需的时间，或者说样品中一半的放射性核发生衰变所需的时间。它是特定同位素的特征性质，不受外部条件影响。衰变遵循指数规律，但在 IGCSE 简单计算中可采用逐次减半的方法。
If an isotope has a half‑life of 2 days, starting with 1000 undecayed nuclei, after 2 days 500 remain, after 4 days 250 remain, after 6 days 125 remain, and so on. The count rate (measured with a Geiger‑Müller tube) also halves each half‑life, after correcting for background radiation.
如果一种同位素的半衰期为 2 天，从 1000 个未衰变核开始，2 天后剩余 500 个，4 天后剩余 250 个，6 天后剩余 125 个，依此类推。计数率（用盖革‑米勒管测量）在扣除本底辐射后，每经过一个半衰期也减半。
Dating artifacts: carbon‑14 (half‑life 5730 years) is used to date organic materials. By comparing the proportion of carbon‑14 remaining to that in living tissue, archaeologists can estimate the age of the sample.
文物年代测定：碳‑14（半衰期 5730 年）用于测定有机材料的年代。通过比较剩余碳‑14 的比例与活体组织中的比例，考古学家可以估算样本的年龄。
9. Uses of Radioactive Isotopes | 放射性同位素的应用
Radioisotopes have many applications in medicine, industry and research. In medicine, technetium‑99m is a gamma emitter used as a tracer to image organs such as the thyroid, kidneys or bones. Its short half‑life (6 hours) minimises radiation dose to the patient. Iodine‑131 is used both for thyroid imaging and for treating hyperthyroidism and thyroid cancer because it accumulates in the thyroid gland.
放射性同位素在医学、工业和研究中有许多应用。在医学上，锝‑99m 是一种 γ 发射体，用作示踪剂以对甲状腺、肾脏或骨骼等器官成像。其半衰期短（6 小时），可最小化患者所受辐射剂量。碘‑131 既用于甲状腺成像也用于治疗甲亢和甲状腺癌，因为它会积聚在甲状腺中。
In industry, uranium‑235 is used as fuel in nuclear reactors, where controlled fission reactions produce energy. Cobalt‑60 is a strong gamma emitter used to sterilise medical equipment and to treat certain cancers through external radiotherapy. Leak detection in pipes can be carried out by adding a gamma‑emitting tracer to the fluid.
在工业中，铀‑235 用作核反应堆的燃料，通过受控裂变反应产生能量。钴‑60 是一种强 γ 发射体，用于对医疗设备进行消毒，并通过体外放射疗法治疗某些癌症。管道泄漏检测可以通过在流体中加入 γ 发射体示踪剂来进行。
Smoke detectors often contain a small amount of americium‑241, an alpha emitter. The alpha particles ionise air molecules, allowing a small current to flow. Smoke particles disrupt the current, triggering the alarm.
烟雾探测器通常含有少量镅‑241，一种 α 发射体。α 粒子使空气分子电离，允许微小电流通过。烟雾颗粒会扰乱电流，从而触发警报。
10. Safety Precautions | 安全防护措施
Because ionising radiation can damage living cells and DNA, causing cancers or radiation sickness, strict safety measures are essential when handling radioactive sources. The three key principles are time, distance and shielding. Minimise the time spent near a source, maximise distance from it (intensity follows an inverse‑square law), and use appropriate shielding: thick lead for gamma, aluminium for beta, and even paper for alpha – though alpha sources are usually sealed because they are dangerous if ingested or inhaled.
由于电离辐射会损伤活细胞和 DNA，导致癌症或放射病，处理放射源时必须采取严格的安全措施。三个关键原则是：时间、距离和屏蔽。尽量减少靠近放射源的时间，最大化与源的距离（强度遵从平方反比定律），并使用适当的屏蔽：γ 用厚铅屏蔽，β 用铝屏蔽，α 甚至用纸即可——但 α 源通常要密封，因为如果摄入或吸入会非常危险。
Gloves, tongs and forceps should be used to avoid direct contact. Radioactive materials must be stored in lead‑lined containers and clearly labelled with the trefoil radiation symbol. The background count should always be measured and subtracted from experimental readings. In school laboratories, only low‑activity sealed sources are used, and records must be kept.
应使用手套、钳子和镊子以避免直接接触。放射性物质必须存放在铅衬容器中，并清晰标记三叶形辐射标志。本底计数应始终测量并从实验读数中扣除。在学校实验室中，只使用低活度的密封源，并且必须做好记录。
11. Background Radiation and Measurement | 本底辐射与测量
Background radiation is the low‑level radiation that is always present in the environment. It originates from cosmic rays, rocks and soil (e.g., radon gas), building materials, food (e.g., bananas contain potassium‑40) and even medical procedures. The amount varies by location – areas with granite rocks often have higher background levels.
本底辐射是环境中始终存在的低水平辐射。它来源于宇宙射线、岩石和土壤（如氡气）、建筑材料、食物（如香蕉含钾‑40），甚至医疗过程。辐射水平因地点而异——花岗岩地区通常本底较高。
To measure radioactivity, a Geiger‑Müller (GM) tube connected to a counter is commonly used. The corrected count rate is obtained by subtracting the background count rate from the measured count rate. All discussions of half‑life require this correction.
为测量放射性，常使用连接计数器的盖革‑米勒（GM）管。修正后的计数率通过从实测计数率中减去本底计数率得到。所有半衰期讨论都需要这项修正。
12. Summary and Exam Tips | 总结与考试技巧
Radioactivity is a key topic in Edexcel IGCSE Science. Students must be able to describe the nature and properties of alpha, beta and gamma radiation, write balanced nuclear equations, interpret half‑life graphs, and evaluate uses and risks. Remember to revise the difference between ionisation and penetration, deflection in fields, and the safety precautions.
放射性是 Edexcel IGCSE 科学的一个关键主题。学生必须能够描述 α、β 和 γ 辐射的本质和性质，书写平衡核方程，解读半衰期图，并评价用途和风险。记住要复习电离与穿透的区别、电场和磁场中的偏转以及安全防护措施。
In exams, always balance the top and bottom numbers in equations, and show your working when calculating half‑life problems. Be prepared to explain why certain isotopes are chosen for specific uses based on half‑life and type of radiation. Finally, use precise scientific language, such as ‘random process’ and ‘spontaneous decay’, to gain full marks.
考试中，务必使方程上下数字平衡，并在计算半衰期问题时展示解题步骤。准备好解释为何根据半衰期和辐射类型选择特定同位素用于特定用途。最后，使用精确的科学语言，如“随机过程”和“自发衰变”，以获取满分。
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