📚 Fission & Fusion | 裂变与聚变
equation E = mc² and play a vital role in energy production, from power stations to stars.
核裂变和核聚变是从原子核中释放巨大能量的反应。裂变是将重核分裂成较小的核，而聚变是将轻核结合成较重的核。这两种过程都与著名的质能方程 E = mc² 相关，并在发电站和恒星等能量产生中发挥着关键作用。
1. Introduction to Nuclear Reactions | 核反应简介
A nuclear reaction changes the composition of an atomic nucleus, resulting in the release or absorption of energy. Unlike chemical reactions, which involve electrons, nuclear reactions involve binding forces within the nucleus and can convert mass into energy on a much larger scale.
核反应会改变原子核的组成，并释放或吸收能量。与涉及电子的化学反应不同，核反应涉及核内的结合力，能够在更大的规模上将质量转化为能量。
2. What is Nuclear Fission? | 什么是核裂变？
Nuclear fission is the process of splitting a heavy, unstable nucleus into two or more smaller nuclei, along with the release of neutrons and a large amount of energy. It is often triggered when a nucleus captures a neutron, becomes highly unstable, and breaks apart almost instantly.
核裂变是将一个重的不稳定核分裂成两个或更多较小核的过程，同时释放出中子和大量能量。通常当一个核捕获一个中子后变得极不稳定，几乎瞬间分裂。
For example, when a uranium-235 nucleus absorbs a slow neutron, it temporarily becomes uranium-236 in an excited state, which then splits into fragments such as barium-141 and krypton-92, plus additional neutrons and kinetic energy.
例如，当铀-235 原子核吸收一个慢中子后，暂时形成激发态的铀-236，然后分裂成钡-141和氪-92等碎片，再加上额外的中子和动能。
²³⁵₉₂U + ¹₀n → [²³⁶₉₂U]* → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3¹₀n + energy
3. Chain Reactions and Critical Mass | 链式反应与临界质量
Each fission event releases two or three neutrons that can go on to cause further fissions. If these neutrons hit other fissile nuclei, a self-sustaining chain reaction can occur, quickly multiplying the number of fissions.
每一次裂变事件释放两到三个中子，这些中子可以引发更多的裂变。如果这些中子撞击其他易裂变核，就会发生自持链式反应，使裂变次数迅速倍增。
The critical mass is the minimum amount of fissile material (such as uranium-235 or plutonium-239) needed to maintain a chain reaction. Below this mass, too many neutrons escape the material without causing further fission, and the reaction dies out.
临界质量是维持链式反应所需的最小易裂变材料（如铀-235或钚-239）的质量。低于这个质量，太多中子会逃逸出材料而未能引发进一步裂变，反应就会中止。
4. Nuclear Fission in Power Stations | 核电站中的核裂变
In a nuclear power station, controlled fission reactions produce heat, which is used to generate steam, drive turbines, and produce electricity. Fuel rods containing uranium-235 pellets are arranged in the reactor core, where a steady chain reaction is maintained.
在核电站中，受控的裂变反应产生热量，用来生成蒸汽，驱动涡轮机发电。包含铀-235芯块的燃料棒排列在反应堆堆芯中，在那里维持稳定的链式反应。
The heat from the core is transferred to a coolant, which circulates through a heat exchanger to turn water into steam in a secondary loop, preventing radioactive material from reaching the turbine. This is similar to how a fossil-fuel power station works, but the heat source is nuclear rather than chemical combustion.
堆芯产生的热量传递给冷却剂，冷却剂通过热交换器循环，在二次回路中将水变成蒸汽，从而防止放射性物质进入涡轮机。这与化石燃料发电站的工作原理相似，但热源是核能而非化学燃烧。
5. Control Rods and Moderators | 控制棒与减速剂
Control rods made of neutron-absorbing materials such as boron or cadmium are used to regulate the rate of the chain reaction. Lowering the control rods deeper into the core absorbs more neutrons and reduces the reaction rate; raising them allows the reaction to speed up.
由硼或镉等中子吸收材料制成的控制棒用于调节链式反应的速率。将控制棒向下插入堆芯越深，吸收的中子越多，反应速率降低；提升控制棒则允许反应加快。
A moderator is a material, such as water or graphite, that surrounds the fuel and slows down the fast neutrons produced by fission. Slower, 'thermal' neutrons are much more likely to cause further fissions in uranium-235, making the reactor more efficient.
减速剂是包围燃料的材料，如水或石墨，用于减缓裂变产生的快中子速度。较慢的“热中子”更有可能在铀-235中引发进一步裂变，从而提高反应堆效率。
6. Nuclear Fusion – The Power of the Stars | 核聚变——恒星的能量
Nuclear fusion is the process in which two light nuclei combine to form a heavier nucleus, releasing energy because the mass of the product is slightly less than the total mass of the reactants. This process powers the Sun and other stars.
核聚变是两个轻核结合形成一个较重核的过程，由于产物的质量略小于反应物的总质量，因此释放能量。这一过程为太阳和其他恒星提供能量。
In the Sun, hydrogen nuclei (protons) fuse through a series of steps to form helium, releasing vast amounts of energy in the form of light and heat. The main fusion reaction in stars converts four protons into a helium-4 nucleus plus two positrons and neutrinos.
在太阳内部，氢核（质子）经过一系列步骤聚变成氦，以光和热的形式释放出巨大的能量。恒星中的主要聚变反应将四个质子转化为一个氦-4核，外加两个正电子和中微子。
4¹₁H → ⁴₂He + 2e⁺ + 2νₑ + energy
7. Conditions for Fusion on Earth | 地球上实现聚变的条件
Bringing about nuclear fusion on Earth requires extremely high temperatures (millions of degrees Celsius) to give the positively charged nuclei enough kinetic energy to overcome their electrostatic repulsion. This is known as overcoming the Coulomb barrier.
在地球上实现核聚变需要极高的温度（数百万摄氏度），以使带正电荷的原子核获得足够的动能，克服它们之间的静电排斥力。这被称为克服库仑势垒。
In addition, the fuel must be confined at a high density for a sufficient amount of time. In experimental fusion reactors such as tokamaks, powerful magnetic fields are used to contain the hot plasma, while inertial confinement uses lasers to compress a fuel pellet.
此外，燃料必须在高密度下被约束足够长的时间。在托卡马克等实验性聚变反应堆中，强大的磁场被用来约束高温等离子体，而惯性约束则利用激光压缩燃料小球。
Currently, sustained and net-energy-gain fusion reactions have not yet been achieved for commercial electricity generation, but international projects like ITER aim to demonstrate the feasibility of fusion power.
目前，持续产生净能量增益的聚变反应尚未实现商业发电，但像 ITER 这样的国际合作项目旨在证明聚变能的可行性。
8. Comparing Fission and Fusion | 裂变与聚变的比较
| Aspect | 方面 | Fission | 裂变 | Fusion | 聚变 |
| Process | Splitting a heavy nucleus | Joining light nuclei |
| Typical fuel | Uranium-235, plutonium-239 | Hydrogen isotopes (deuterium, tritium) |
| Energy released per reaction | ~200 MeV per fission | ~17.6 MeV per D-T fusion |
| Conditions | Neutron capture, critical mass | Extremely high temperature and pressure |
| Radioactive waste | Produces long-lived radioactive waste | Much less long-lived radioactive waste |
| Current use | Commercial power stations | Experimental stages; not yet commercial |
Fission is well-established for electricity generation but carries risks of accidents and produces hazardous waste. Fusion offers the promise of almost limitless clean energy, yet the technical challenges of containment and ignition remain significant.
裂变技术已成熟用于发电，但存在事故风险和产生危险废料。聚变提供了几乎无限清洁能源的前景，但约束和点火方面的技术挑战依然巨大。
9. Mass Defect and Binding Energy | 质量亏损与结合能
The total mass of a stable nucleus is always less than the sum of the masses of its individual protons and neutrons. This difference is called the mass defect. The missing mass has been converted into the binding energy that holds the nucleus together.
稳定原子核的总质量总是小于其各个质子和中子的质量之和。这个差值称为质量亏损。亏损的质量转化为了将核子结合在一起的结合能。
The greater the binding energy per nucleon, the more stable the nucleus. Iron-56 has a very high binding energy per nucleon, which makes it one of the most stable nuclei. Both fission and fusion proceed in the direction of increasing binding energy per nucleon, releasing the energy difference.
每个核子的平均结合能越大，原子核越稳定。铁-56 具有很高的核子平均结合能，使其成为最稳定的核素之一。裂变和聚变都朝着核子平均结合能增大的方向进行，释放出能量差。
10. E = mc² and Energy Released | 质能方程与能量释放
Einstein's mass– hat mass can be converted into energy and vice versa. In nuclear reactions, a small amount of mass is converted into a huge amount of energy, because the speed of light squared (c²) is a very large number.
爱因斯坦的质能方程 E = mc² 指出，质量可以转化为能量，反之亦然。在核反应中，少量的质量会转化为巨大的能量，因为光速的平方（c²）是一个非常大的数值。
ated by ΔE = Δm × c². For fission of one uranium-235 nucleus, the mass defect is about 0.1% s, yet the energy is millions of times greater than that from a typical chemical reaction.
如果测量生成物的总质量并与反应物比较，你会发现一个微小的质量差 Δm。释放的能量由 ΔE = Δm × c² 计算得出。对于单个铀-235核的裂变，质量亏损约是原始质量的 0.1%，但能量却是典型化学反应的数百万倍。
11. Calculating Energy Released (Simple Example) | 能量释放计算（简单例子）
the products is slightly less than the total mass of the reactants. Suppose the mass defect is found to be 0.186 u.
考虑裂变反应：²³⁵U + n → ¹⁴¹Ba + ⁹²Kr + 3n。产物的总质量略小于反应物的总质量。假设质量亏损为 0.186 u。
Using the conversion 1 u = 931.5 MeV, the energy released is:
利用换算关系 1 u = 931.5 MeV，释放的能量为：
E = 0.186 u × 931.5 MeV/u ≈ 173 MeV
This enormous energy from a single fission event, when multiplied by the billions of reactions per second in a reactor, produces the thermal power that drives turbines.
单个裂变事件所释放的巨大能量，再乘以反应堆中每秒发生的数十亿次反应，就产生了驱动涡轮机的热能。
12. Environmental and Safety Considerations | 环境与安全考虑
Nuclear fission produces radioactive waste that remains hazardous for thousands of years. Safe disposal, such as deep geological storage, is essential to isolate it from the environment. Accidents, such as those at Chernobyl and Fukushima, highlight the potential risks of radiation release.
核裂变产生的放射性废料在数千年内仍具有危险性。像深层地质储存这样的安全处置方法对于将其与环 境隔离至关重要。切尔诺贝利和福岛等事故凸显了辐射释放的潜在风险。
Fusion is inherently safer, because the reaction stops immediately if confinement fails, and it produces minimal long-lived radioactive waste. However, fusion research facilities still handle radioactive materials, such as tritium, and neutron activation of reactor walls creates low-level waste.
聚变固有地更安全，因为一旦约束失效，反应就会立即停止，并且产生极少的长寿命放射性废料。然而，聚变研究设施仍需处理像氚这样的放射性物质，反应堆壁的中子活化也会产生低水平废料。
Both fission and fusion contribute to a low-carbon energy mix, but continued research into safer reactor designs, waste management, and sustainable fusion are critical for the global energy future.
裂变和聚变都有助于低碳能源结构，但在更安全的反应堆设计、废物管理和可持续聚变方面进行持续研究，对全球能源的未来至关重要。
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