📚 IGCSE Physics: Nuclear Fission vs Nuclear Fusion | IGCSE物理：核裂变与核聚变对比
Nuclear fission and nuclear fusion are two fundamental processes that release energy from the nucleus of an atom. Fission splits a heavy nucleus into smaller fragments, while fusion joins light nuclei to form a heavier one. Both processes convert a small amount of mass into a large amount of energy, following Einstein’s equation E = mc². This article compares the two processes with a focus on the Edexcel IGCSE Physics specification.
核裂变和核聚变是从原子核释放能量的两种基本过程。裂变将一个重核分裂成较小的碎片，而聚变将轻核结合成一个较重的核。这两个过程都会将少量质量转化为大量能量，遵循爱因斯坦的方程 E = mc²。本文结合 Edexcel IGCSE 物理考纲，对这两种过程进行详细对比。
1. What is Nuclear Fission? | 什么是核裂变？
Nuclear fission is a process in which a heavy nucleus, such as uranium-235, absorbs a neutron and becomes unstable. The nucleus then splits into two smaller nuclei (fission fragments), releasing a large amount of energy and two or three additional neutrons. A typical fission reaction can be written as:
核裂变是指重核（如铀-235）吸收一个中子后变得不稳定，分裂成两个较小的原子核（裂变碎片），并释放大量能量和两到三个额外中子的过程。一个典型的裂变反应可以写成：
²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3¹₀n + Energy
The total mass of the products is slightly less than the total mass of the original nucleus and neutron. This missing mass, called the mass defect, is converted into energy. Even a tiny mass loss releases a huge amount of energy because the speed of light squared (c²) is an enormous number.
反应产物的总质量略小于原始原子核和中子的总质量。这个消失的质量称为质量亏损，它被转化为能量。即使非常微小的质量损失也会释放巨大的能量，因为光速的平方（c²）是一个极其巨大的数字。
2. The Chain Reaction | 链式反应
Each fission event releases two or three neutrons. These neutrons can be absorbed by other uranium-235 nuclei, causing them to fission as well. This creates a self-sustaining sequence of reactions known as a chain reaction.
每一次裂变会释放两到三个中子。这些中子可以被其他铀-235原子核吸收，使它们也发生裂变，从而形成自我维持的反应序列，称为链式反应。
In a nuclear reactor, the chain reaction is carefully controlled. Control rods, made of boron or cadmium, absorb excess neutrons so that exactly one neutron from each fission goes on to cause another fission. If too many neutrons are absorbed, the reactor slows down; if too few, it speeds up. An uncontrolled chain reaction releases energy in an explosive way, which is how an atomic bomb works.
在核反应堆中，链式反应被精确控制。由硼或镉制成的控制棒会吸收多余的中子，使每次裂变恰好有一个中子引发下一次裂变。如果吸收的中子过多，反应堆会减慢；如果吸收过少，反应会加速。不受控制的链式反应会以爆炸方式释放能量，原子弹就是利用这个原理。
The minimum mass of fuel needed to sustain a chain reaction is called the critical mass. Below this mass, too many neutrons escape before causing further fission, so the reaction stops.
维持链式反应所需的最小燃料质量称为临界质量。低于这个质量时，过多的中子在引发下一次裂变之前就逃逸了，反应便会停止。
3. How a Nuclear Reactor Works | 核反应堆的工作原理
A nuclear reactor uses controlled fission to produce heat. The main components include fuel rods, control rods, a moderator, and a coolant.
核反应堆利用可控裂变产生热量。主要部件包括燃料棒、控制棒、慢化剂和冷却剂。
-
Fuel rods contain uranium-235.
燃料棒含有铀-235。
-
Control rods absorb neutrons to slow the reaction.
控制棒吸收中子以减慢反应。
-
The moderator (water or graphite) slows down fast neutrons. Slow neutrons are much more likely to be captured by uranium-235 nuclei than fast neutrons.
慢化剂（水或石墨）使快中子减速。慢中子比快中子更容易被铀-235原子核俘获。
-
The coolant (water or carbon dioxide) removes heat from the core and transfers it to a heat exchanger. The heat turns water into steam, which drives a turbine connected to a generator.
冷却剂（水或二氧化碳）将堆芯的热量带走，并传递到热交换器。热量使水变成蒸汽，推动连接发电机的涡轮机。
This is how nuclear power stations generate electricity without burning fossil fuels.
这就是核电站无需燃烧化石燃料而产生电力的方式。
4. Pros and Cons of Nuclear Fission | 核裂变的优缺点
Nuclear fission is a well-established technology, but it has both benefits and serious drawbacks.
核裂变是一项成熟的技术，但它既有优点，也有严重缺点。
-
Advantage: A small amount of uranium releases a huge amount of energy.
优点：少量铀即可释放大量能量。
-
Advantage: Fission power stations do not release carbon dioxide while operating.
优点：裂变电站运行时不会排放二氧化碳。
-
Advantage: It provides reliable, continuous base-load electricity.
优点：可以提供可靠、连续的基础负荷电力。
-
Disadvantage: Fission produces highly radioactive waste that remains dangerous for thousands of years.
缺点：裂变产生高放射性废料，这些废料在数千年内仍然危险。
-
Disadvantage: There is a risk of nuclear accidents, such as the ones at Chernobyl and Fukushima.
缺点：存在核事故风险，例如切尔诺贝利和福岛事故。
-
Disadvantage: Uranium is a finite resource.
缺点：铀是一种有限资源。
5. What is Nuclear Fusion? | 什么是核聚变？
Nuclear fusion is a process in which two light nuclei combine to form a heavier nucleus. The most practical fusion reaction for energy production involves two isotopes of hydrogen: deuterium (²₁H) and tritium (³₁H).
核聚变是两个轻原子核结合形成一个较重原子核的过程。用于能源生产的最实际聚变反应涉及氢的两种同位素：氘（²₁H）和氚（³₁H）。
²₁H + ³₁H → ⁴₂He + ¹₀n + 17.6 MeV of Energy
This reaction releases far more energy per kilogram of fuel than fission. It is the process that powers the Sun and other stars. Deep inside the Sun, enormous gravitational pressure and a temperature of about 15 million °C force hydrogen nuclei to fuse into helium.
这种反应每千克燃料释放的能量远多于裂变。它是太阳和其他恒星能量的来源。在太阳内部深处，巨大的引力压力以及约1500万摄氏度的温度迫使氢原子核聚变为氦。
In fusion, the mass of the helium nucleus plus the neutron is slightly less than the mass of the two original hydrogen nuclei. This mass difference is released as energy, again described by E = mc².
在聚变中，氦核与中子的质量略小于原来两个氢核的总质量。这个质量差以能量形式释放，同样由 E = mc² 描述。
6. Conditions and Challenges for Fusion | 聚变的条件与挑战
For fusion to happen, the two positively charged nuclei must get close enough together. Because like charges repel each other, this requires overcoming a huge electrostatic repulsion. The nuclei must therefore be moving at extremely high speeds, which means they must be at a very high temperature — around 100 million °C in a fusion reactor.
要使聚变发生，两个带正电的原子核必须靠近到足够距离。由于同种电荷互相排斥，必须克服巨大的静电斥力。因此原子核必须以极快速度运动，也就是说它们必须处于极高温度——聚变反应堆中约需1亿摄氏度。
At these temperatures, matter exists as a plasma, a state where electrons are stripped from the nuclei. On Earth, no material container can withstand such temperatures, so scientists use two main approaches:
在这样的温度下，物质以等离子体状态存在，即电子从原子核上剥离。在地球上，没有任何材料容器能承受如此高温，因此科学家使用两种主要方法：
-
Magnetic confinement: powerful magnets hold the hot plasma in a donut-shaped chamber called a tokamak.
磁约束：强磁场将高温等离子体约束在环形装置“托卡马克”中。
-
Inertial confinement: high-energy lasers compress and heat a small fuel pellet until fusion occurs.
惯性约束：高能激光压缩并加热一个小燃料靶丸，直到发生聚变。
Despite years of research, no fusion reactor has yet produced more energy than it consumes. This remains one of the greatest scientific and engineering challenges of our time.
尽管经过多年研究，尚没有聚变反应堆能够产生超过其消耗的能量。这仍然是当今最伟大的科学和工程挑战之一。
7. Pros and Cons of Nuclear Fusion | 核聚变的优缺点
Fusion is often called the “holy grail” of clean energy because of its enormous potential, but it also has major difficulties.
聚变常被称为清洁能源的“圣杯”，因为它潜力巨大，但也面临重大困难。
-
Advantage: Fusion releases more energy per kilogram than fission.
优点：聚变每千克燃料释放的能量多于裂变。
-
Advantage: Deuterium is found in seawater and is almost unlimited. Tritium can be produced from lithium, which is also abundant.
优点：海水中含有大量氘，几乎取之不尽。氚可由储量丰富的锂生产。
-
Advantage: Fusion produces much less long-lived radioactive waste than fission.
优点：聚变产生的长寿命放射性废料远少于裂变。
-
Advantage: There is no risk of a meltdown, because the reaction stops if the plasma is not carefully controlled.
优点：没有堆芯熔毁风险，因为如果等离子体未被精确控制，反应就会停止。
-
Disadvantage: Achieving fusion on Earth is extremely difficult and requires enormous temperatures and pressures.
缺点：在地球上实现聚变极其困难，需要极高的温度和压力。
-
Disadvantage: Current fusion experiments require more energy to run than they produce.
缺点：目前的聚变实验消耗的能量多于产生的能量。
-
Disadvantage: Materials in the reactor must survive extreme heat and neutron radiation.
缺点：反应堆中的材料必须承受极端高温和中子辐射。
8. Comparing Fission and Fusion | 核裂变与核聚变的对比
The table below summarises the key differences between nuclear fission and nuclear fusion for the IGCSE exam.
下表总结了核裂变与核聚变在 IGCSE 考试中的关键区别。
| Property | Nuclear Fission | Nuclear Fusion |
|---|---|---|
| Process 过程 |
Splits a heavy nucleus 分裂重核 |
Joins light nuclei 结合轻核 |
| Fuel 燃料 |
Uranium-235 or plutonium 铀-235或钚 |
Hydrogen isotopes (deuterium and tritium) 氢同位素（氘和氚） |
| Conditions 条件 |
Room temperature with neutron bombardment 室温下用中子轰击 |
Extremely high temperature (about 100 million °C) 极高温度（约1亿摄氏度） |
| Energy per kg 每千克能量 |
Very large 非常大 |
Even larger 更大 |
| Radioactive waste 放射性废料 |
Highly radioactive for a long time 长时间高放射性 |
Much less radioactive 放射性低得多 |
| Safety risk 安全风险 |
Risk of accidents and meltdown 有事故和熔毁风险 |
No meltdown risk; reaction stops if plasma is lost 无熔毁风险；等离子体失控时反应停止 |
| Control 控制难度 |
Easier to control; used in power stations today 较容易控制；已用于发电站 |
Very difficult; still mainly experimental 非常困难；仍主要在实验阶段 |
| Natural occurrence 自然发生 |
Does not occur naturally on Earth 地球上不会自然发生 |
Occurs naturally in the Sun and stars 在太阳和恒星中自然发生 |
9. Key Points for the IGCSE Exam | IGCSE 考点总结
Make sure you can do the following for the Edexcel IGCSE Physics paper.
确保你能完成以下内容，以应对 Edexcel IGCSE 物理试卷。
-
Define nuclear fission as the splitting of a heavy nucleus into two smaller nuclei.
定义核裂变：重核分裂成两个较小原子核的过程。
-
Define nuclear fusion as the joining of two light nuclei to form a heavier nucleus.
定义核聚变：两个轻核结合成一个较重原子核的过程。
-
Write and balance nuclear equations for fission and fusion using mass numbers and atomic numbers.
利用质量数和原子序数写出并配平裂变和聚变的核反应方程。
-
Explain how a chain reaction works and how control rods and a moderator are used in a reactor.
解释链式反应的工作原理，以及反应堆中控制棒和慢化剂的用途。
-
Describe the conditions required for fusion and why it is difficult to achieve.
描述聚变所需条件以及为什么难以实现。
-
Use mass defect and E = mc² to explain the energy released in nuclear reactions.Published by TutorHao | IGCSE Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导