Nuclear Radiation: Uses, Fission and Fusion
Nuclear Fission
Nuclear fission is the splitting of a large, unstable nucleus into two smaller daughter nuclei. This process releases a large amount of energy, along with two or three neutrons and gamma radiation. Fission can occur spontaneously in very unstable isotopes, but in nuclear reactors it is induced by bombarding a fissile nucleus (such as uranium-235 or plutonium-239) with a slow-moving neutron.
When a uranium-235 nucleus absorbs a neutron, it becomes unstable and splits. The two daughter nuclei and the released neutrons carry away kinetic energy. The total mass of the products is slightly less than the mass of the original nucleus plus the neutron — this “missing” mass has been converted into energy according to Einstein’s equation \(E = mc^2\).
In nuclear fission, the neutrons released can go on to cause further fission events. If at least one neutron from each fission causes another fission, a self-sustaining chain reaction occurs.
In a nuclear power station, the chain reaction must be controlled so that exactly one neutron from each fission event causes another fission. Control rods (made of boron or cadmium) absorb excess neutrons. Lowering the rods into the reactor core slows the reaction; raising them speeds it up.
A moderator (usually water or graphite) slows down fast-moving neutrons. Slow neutrons are more likely to be absorbed by uranium-235 nuclei, making fission more likely. The energy from fission heats a coolant (often water), which produces steam to drive turbines connected to generators, producing electricity.
Nuclear Fusion
Nuclear fusion is the process where two light nuclei join together to form a larger nucleus. This releases a huge amount of energy — even more per kilogram than fission. Fusion is the process that powers stars, including our Sun. In the Sun’s core, hydrogen nuclei fuse to form helium at temperatures of around 15 million °C.
Fusion is difficult to achieve on Earth because the nuclei are positively charged and repel each other. To overcome this electrostatic repulsion, extremely high temperatures and pressures are needed to force the nuclei close enough together for the strong nuclear force to take over and bind them. Maintaining these conditions long enough to sustain a fusion reaction is a major engineering challenge.
Both fission and fusion release energy because the products have a higher binding energy per nucleon than the reactants. The “missing” mass is converted to energy via \(E = mc^2\).
Fission splits large nuclei (like uranium-235) and is used in current nuclear power stations. It produces radioactive waste that must be stored safely for thousands of years. Fusion joins small nuclei (like hydrogen isotopes) and produces far less radioactive waste. However, no commercially viable fusion reactor exists yet because of the extreme conditions required.
Both processes convert a small amount of mass into a large amount of energy. Fusion releases more energy per kilogram of fuel and uses hydrogen (abundant in seawater) as fuel, making it a potentially clean and almost unlimited energy source for the future.
Uses of Nuclear Radiation
Nuclear radiation has many practical applications beyond power generation. In medicine, gamma rays are used in radiotherapy to destroy cancer cells. A focused beam of gamma radiation is aimed at a tumour from multiple angles, concentrating the dose on the cancer while minimising damage to healthy tissue. Radioactive tracers (such as technetium-99m) are injected into the body and tracked using a gamma camera to diagnose conditions like blocked blood vessels or organ function problems.
In industry, beta or gamma sources are used to monitor the thickness of materials during manufacturing. If the material gets too thick, less radiation passes through to the detector, triggering an adjustment. Gamma radiation is also used to sterilise medical equipment and food, killing bacteria without chemicals or heat.
The choice of radiation type depends on its penetrating power and ionising ability. Alpha particles are highly ionising but have very low penetration — they are stopped by a few centimetres of air or a sheet of paper. They are used in smoke detectors, where alpha particles ionise air between two electrodes. When smoke enters, it absorbs the alpha particles, the current drops, and the alarm sounds.
Beta particles penetrate further (stopped by a few millimetres of aluminium) and are used for thickness monitoring of thin materials like paper or aluminium foil. Gamma rays are the most penetrating (only significantly reduced by thick lead or concrete) and are chosen for sterilisation and medical imaging because they can pass through the body.
Nuclear Waste and Safety
Nuclear fission produces radioactive waste, which is categorised as low-level, intermediate-level or high-level depending on its activity and half-life. Low-level waste (contaminated clothing, tools) is compacted and stored in lined, shallow trenches. Intermediate-level waste is mixed with concrete and stored in steel containers. High-level waste (spent fuel rods) generates significant heat and must be cooled before being vitrified (turned into glass) and stored deep underground in geological repositories.
Safety precautions when handling radioactive materials include: keeping exposure time as short as possible, maintaining maximum distance from the source, using appropriate shielding (lead-lined containers, thick concrete walls), and monitoring exposure with film badges or electronic dosimeters.