Nuclear fission is how we split a large atomic nucleus into smaller particles. This split creates a huge amount of energy, which impacts our daily lives. For example, the energy created by nuclear power plants is achieved with nuclear fission. It explains how we can create energy from atomic reactions, how nuclear reactors work, how nuclear weapons are produced and even medical treatments using radiation.
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What is Nuclear Fission?
A large, atomic nucleus (like Uranium-235) is split into 2 smaller nuclei and this leads to fission. The nucleus is unstable and absorbs neutrons to trigger this reaction. The nuclei created in the reaction are called daughter nuclei. This process turns a small amount of mass into a large amount of energy, as shown by Einstein's equation: E = mc2. It also creates additional neutrons and gamma rays.
Everything begins when a neutron collides with the nucleus, making it highly unstable so that it splits into two nuclei. The daughter nuclei are normally Barium-141 and Krypton-92. The neutrons emitted in the fission can collide with other nuclei, causing them to split as well, creating more neutrons and continuing a chain reaction. This reaction needs to be controlled at a steady rate to avoid a rapid release of energy, such as a nuclear explosion.
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What particles are normally released in nuclear fission?
The process of Nuclear Fission
Fission has key steps that turn an unstable nucleus into smaller, stable fragment while also releasing vast amounts of energy:
- Neutron absorption: Everything starts when a free neutron collides with the nucleus of a fissile material, such as Uranium-235. The nucleus absorbs this neutron, making it highly unstable. The new nucleus is called Uranium-236.
- Nucleus splitting: The splitting of a large and unstable Uranium-236 nucleus creates two smaller nuclei. These fragments are about half the mass of the original nucleus. Common products created include Barium-141 and Krypton-92.
- Release of neutrons and gamma rays: 2 or 3 neutrons with kinetic energy are normally emitted during the fission. Gamma rays - energised photons - are also released.
- Energy release: Approximately 200 million electron volts (MeV) are created in a fission event. It is distributed among the kinetic energy present in the fission fragment and the energy carried away by the gamma rays. This energy is released as heat when the neutrons slow down, which is used to create electricity.
- Chain reaction: The neutrons emitted in the reaction can collide with other nuclei to create further fission reactions. This ongoing fission is called a chain reaction. Control rods (such as boron) are used in nuclear reactors to moderate the rate of the chain reaction and keep it at a steady level.
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Why are control rods present in a nuclear reactor?
Products of Nuclear Fission
The fission of an unstable, large nucleus creates products that include smaller nuclei, neutrons, gamma rays and energy:
- Fission fragments: Fission splits the nucleus into two smaller nuclei. These fragments are normally unstable and radioactive, decaying into stable forms by emitting beta particles. Common fragments include Barium-141 and Krypton-92.
- Neutrons: Two or three neutrons are produced per fission. These neutrons collide with other nuclei to sustain the chain reaction. The amount of neutrons created per fission varies but is 2.5 on average.
- Gamma rays: Gamma rays are high-energy electromagnetic waves created in nuclear fission. These energised photons are a form of ionising radiation - they can pass through materials and are a key concern in radiation protection.
- Energy release: A small mass is turned into a huge amount of energy during fission. Einstein's equation expresses this (E = mc2). The fragments and neutrons possess kinetic energy and the gamma rays have electromagnetism. A normal fission event releases 200 million electron volts (MeV):
- 85% of the energy is kinetic from the fragments.
- 5% is kinetic energy from the neutrons.
- 10% is lost through gamma rays as electromagnetic radiation.
- Radioactive decay products: The fragments from the fission are radioactive and undergo a series of beta decay that emit beta particles and gamma rays. Eventually, they will reach stable isotopic forms. The decaying process adds to the radioactivity and is an important consideration in nuclear waste management.
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What are the main products created during fission?
Applications of Nuclear fission and fusion
Nuclear fission is applied in various ways, including energy production, medical treatments and the military:
- Power plants: Fission generates electricity. A nuclear power plant uses the heat from fission to produce steam. This drives turbines to turn the generators, turning thermal into electrical energy. They are a major source of low-carbon electricity, an increasingly important source of energy in a world addressing climate change.
- Nuclear reactors for research and medical isotope production: Nuclear reactors are also used for research and to create medical isotopes. Research reactors help in studying nuclear reactions and materials. Medical isotopes produced are used in diagnostic imaging and cancer treatment. An example is Technetium-99m.
- Nuclear weapons: An atomic bomb is an uncontrolled fission chain reaction. It creates an exploding by releasing an enormous amount of energy in a short time. They are devasting weapons that are a global security concern since they were first used in World War II by the United States. Atomic bombs normally contain radioactive isotopes of uranium or plutonium. Various treaties and international agreements have called for non-proliferation.
- Marine propulsion: The submarines and aircraft carriers of some nations are powered by nuclear fission, notably the United Kingdom and the United States. This allows the vessels to stay at sea for long periods without refuelling, giving them increased endurance and operational capability.
- Space exploration: Ongoing experiments are testing the use of nuclear fission to power spacecraft. Nuclear fuel could provide a reliable, long-term power source for deep space missions, allowing for exploration beyond the current capabilities of spacecraft.
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How is nuclear fission used in medicine?
Safety and control measures
The risks of any accident caused by nuclear fission means safety and control are paramount. These are the main steps taken to ensure the reaction is stable and controlled:
- Control rods: These rods are formed from materials that absorb neutrons, such as boron, cadmium, or hafnium. They regulate the fission reaction by being inserted or withdrawn from the reactor core depending on the state of the fission. They allow operators to control the rate of the chain reaction. Inserting rods slows the reaction by absorbing neutrons. Withdrawing rods speeds up the reaction by allowing more neutrons to strike nuclei.
- Moderator: The moderator is a material that slows the neutrons created in fission, normally water or graphite. Slower neutrons are more likely to produce fission. The moderator therefore helps to maintain a controlled chain reaction.
- Coolant: Water is circulated throughout the reactor core to remove heat created by fission. This heat is used to create steam to drive the turbines that generate electricity. Coolant is essential to prevent overheating and meltdown.
- Containment structures: A robust structure is used to contain the nuclear reactor. These structures are made of thick concentre and steel to withstand extreme conditions and contain radiation in the event of an accident.
- Safety systems and protocols: There are numerous safety systems in place to ensure the reactor always operates in a safe window. This includes automatic shutdown if abnormal conditions arise, emergency cooling systems and regular safety drills for personnel. There are also backups for critical systems if anything fails at the plant.
- Waste management: Fission leads to radioactive waste. This waste needs to be handled and disposed of securely to avoid damaging the surrounding environment. Spent nuclear fuel and other radioactive waste are stored in secure facilities, often in deep geological repositories.
- Regulatory oversight: There are strict regulations and national and international bodies that oversee the running of nuclear power plants. These frameworks make sure that all areas of nuclear safety are maintained to a high standard and help to minimise any potential risks.
Final thoughts on Nuclear Fusion - GCSE Physics
Nuclear fission is a cornerstone of modern science, used in fields as varied as energy and medicine. We have seen that there's a huge amount of energy stored in the nucleus of an atom, which fission unlocks. It helps us to appreciate the scientific principles that are present in our society, including how we generate electricity and its increasing importance as humanity searches for low-carbon alternatives to fossil fuels. However, fusion requires strict handling and regulation of safety and waste management. To learn more about nuclear fission, follow the link to read the Max Planck Institute's article on the discovery of fission.
If you need more help getting to grips with how nuclear fission works, TeachTutti have a list of qualified GCSE Science tutors to give you one-on-one preparation in your revision notes for your exam, whether it is AQA GCSE, OCR or Edexcel. Our tutors are experienced with the curriculum for all exam boards.
Frequently asked questions
This is the process when a large, unstable atomic nucleus splits into 2 smaller nuclei, along with a few neutrons. It creates a huge amount of energy. Nuclear fission can happen naturally or induced by attacking the nucleus with neutrons.
The process converts mass into energy by splitting the nucleus. A fission reaction will have kinetic energy from the fragments and also gamma rays. Einstein's equation shows the conversion: E = mc2.
Splitting the original nucleus creates two smaller nuclei, called fission fragments. It also creates free neutrons and gamma rays.
A chain reaction is a series of reactions that are self-substaining. This happens when the neutrons released in the fission trigger further reactions in the nuclei. A chain reaction is crucial to how nuclear reactors operate and why nuclear weapons have such destructive capabilities.
Control rods are used in a nuclear reactor. This controls the fission by absorbing excess neutrons and moderators. This slows down the neutrons and maintains the chain reaction at a steady speed. There is also a cooling system and containment structure for security.
The process is used to generate electricity, produce medical isotopes and power naval vessels including submarines. It is also used in nuclear weapons.
The risks include radiation exposure, nuclear accidents, such as the Chernobyl disaster in 1986 and the long-term management of radioactive waste.
It is a much cleaner energy source than fossil fuel, with low greenhouse gas emissions in nuclear fission. It does create radioactive waste that needs to be managed so it doesn't contaminate the nearby environment.
Yes, it can. There was a natural nuclear fission reactor in Oklo (Gabon, Africa) which used to be active 2 billion years ago.
Nuclear fission splits a large atomic nucleus. Nuclear fusion combines small nuclei into a larger one, releasing more energy. It's the same process that powers the sun. However, nuclear fusion remains a challenge as a controlled fusion that creates sufficient energy.
Glossary
- Nuclear fission - The process when a large atomic nucleus splits into two smaller nuclei. This releases energy, neutrons and gamma rays.
- Uranium-235 - A fissile isotope used in nuclear reactors and weapons. It undergoes fission when it absorbs a neutron.
- Neutron - A subatomic particle found in an atom's nucleus. It doesn't have electric charge. Neutrons initiate and sustain nuclear fission reactions.
- Daughter nuclei - The smaller nuclei created during nuclear fission.
- Gamma rays - High-energy electromagnetic radiation that is emmitted during fission. It carries away some of the energy created by the process.
- Chain reaction - A series of fission reactions that are self-sustaining. Each neutron realsed from the fission causes additional fission events.
- Control rods - Devices that regulate the speed of the fission chain reaction. They are made of neutron-absorbing materials, such as boron or cadmium.
- Moderator - A material used to slow down neutrons and increase further reactions. Common moderators are water and graphite.
- Coolant - A fluid that removes heat created during fission by circulating it through the reactor.
- Fission fragments - The nuclei created by splitting the atomic nucleus during fission.
- Kinetic energy - The energy of motion. This is the energy created in the fragments and neutrons during fission.
- Radioactive decay - When nuclei lose energy by emitting radiation, beta particles and gamma rays. This decay is unstable.
- Spent nuclear fuel - Nuclear fuel that has been used in a reactor. It is highly radioactive and can't be used any longer to sustain a fission chain reaction.
- Containment structure - The structure that surrounds a reactor to contain the release of any materials if an accident occurs.
- Einstein’s equation - A formula to express the equivalence of mass and energy. It explains how a small amount of mass can be converted into a large amount of energy.
- Fissile material - Material that can sustain a nuclear fission chain reaction with neutrons. This includes Uranium-235 and Plutonium-239.
- Nuclear reactor - A device that initialises and controls a nuclear fission chain reaction.
- Nuclear waste - Radioactive materials that remain after the fuel has been used in a nuclear reactor. This waste needs careful management and disposal.
- Nuclear fusion - When two light atomic nuclei combine to create a heavier nucleus and generate energy. Fusion is how the sun is powered and differs from fission, which splits nuclei.
