Nuclear Fission and Fusion

Nuclear physics is a branch of physics that studies atomic nuclei and their interactions. In this context, two important processes are nuclear fission and nuclear fusion. Both processes involve changing the nuclei of atoms, leading to the emission or absorption of energy. Understanding these processes forms the basis of nuclear technology used in various industries today.

What is nuclear fission?

Nuclear fission is a type of reaction in which the nucleus of an atom splits into two or more smaller nuclei, while simultaneously releasing a considerable amount of energy. This process usually occurs in heavier elements, such as uranium or plutonium, which have larger nuclei. The fission process releases neutrons, which can further the fission reactions, causing a chain reaction. A common material used in nuclear fission is uranium-235.

How does nuclear fission occur?

Let's see how nuclear fission occurs using the example of uranium-235:

n + 235 U → 236 U → 141 Ba + 92 Kr + 3n + energy

In this equation, a neutron (n) collides with a uranium-235 (²³⁵ U) nucleus. Uranium absorbs the neutron and becomes uranium-236 (²³⁶ U), an unstable isotope. This unstable nucleus splits into two lighter nuclei, barium-141 (¹⁴¹ Ba) and krypton-92 (⁹² Kr), releasing an additional free neutron and a considerable amount of energy.

Chain reaction

The neutrons released from the fission process can collide with other uranium-235 nuclei. This releases more neutrons and the reaction propagates continuously – a process known as a chain reaction. In nuclear reactors, this chain reaction is controlled to produce electricity, while in nuclear weapons, it is allowed to happen all at once, resulting in an explosion.

Visual example of nuclear fission

What is nuclear fusion?

Nuclear fusion is the process in which two lighter atomic nuclei combine to form a heavier nucleus, releasing energy in the process. This reaction powers the Sun and other stars. Fusion is often touted as the ultimate clean energy source because it produces much more energy than fission and produces negligible nuclear waste. Fusion typically involves isotopes of hydrogen, such as deuterium and tritium.

How does nuclear fusion occur?

Fusion requires extremely high temperatures and pressures to bring the nuclei close enough to overcome nuclear forces. A common nuclear fusion reaction is the combination of deuterium and tritium:

2H + 3H → 4 He + n + energy

In this reaction, deuterium (² H) and tritium (³ H) combine to produce helium-4 (⁴ He), a free neutron (n), and a lot of energy. The energy released in fusion is due to the difference in the binding energy between the products and the reactants.

Visual example of nuclear fusion

Challenges in achieving fusion on Earth

Achieving nuclear fusion on Earth poses significant challenges because of the extremely high temperatures and pressures required. These conditions are necessary to overcome the electrostatic forces that push the positively charged nuclei away from one another. Fusion reactors known as tokamaks or inertial confinement systems are being developed to achieve these conditions permanently.

Comparison between fission and fusion

Nuclear fission and fusion are both powerful reactions that release tremendous energy. However, they have key differences:

1. Reaction type:
   - Fission: splitting of a large nucleus into smaller nuclei.
   - Fusion: combining smaller nuclei to form a larger nucleus.

2. Energy requirement:
   - Fission: This requires a critical mass and can be initiated with a neutron.
   - Fusion: This requires extremely high temperatures and pressures.

3. Energy production:
   - Fission: This produces energy, but not as much as fusion.
   - Fusion: Produces more energy than fission.

4. By-products:
   - Fission: produces radioactive waste.
   - Fusion: Produces relatively harmless helium.

5. Current use:
   - Fission: used in nuclear reactors and atomic bombs.
   - Fusion: Research is still ongoing for practical energy production.

Applications of nuclear fission

Nuclear fission is currently used in nuclear power plants to produce electricity. It is also used in submarines and military ships to provide large amounts of energy without refueling frequently. Another application is in nuclear weapons, which have significant destructive capabilities.

Possibility of nuclear fusion

Nuclear fusion promises to provide a nearly unlimited and clean energy source. Unlike fission, fusion reactions produce little radioactive waste and involve abundant fuels such as hydrogen isotopes. If scientists successfully use fusion sustainably, it could revolutionize the way we produce electricity.

Lesson example - Fusion power plant concept

A fusion power plant would operate by maintaining a 'plasma' of hydrogen isotopes at high temperatures. Techniques such as magnetic confinement and laser-based inertial confinement are being explored. However, maintaining the conditions for a sustained reaction is complex.

Conclusion

Nuclear fission and fusion are the cornerstones of modern nuclear physics, with fission currently dominating practical applications. Fusion remains an area of intense research because of its potential as a clean alternative for providing energy. Understanding these processes enhances our ability to develop safer and more efficient means of harnessing nuclear energy.

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