Uses and Dangers of Radiation
Uses of Radioactive Materials in Medicine
Radioactive materials have many practical applications in medicine. The choice of isotope depends on the type of radiation emitted, the half-life and the toxicity to the patient.
• Medical tracers: a patient swallows or is injected with a radioactive tracer. The tracer is a gamma-emitting isotope with a short half-life. Gamma rays pass through the body and are detected externally, allowing doctors to create images of internal organs and diagnose conditions such as cancer or kidney blockages. A short half-life ensures the patient’s radiation exposure is brief.
• Radiotherapy: high doses of gamma rays or beta particles are targeted at cancerous tumours to kill the rapidly dividing cancer cells. The beam is rotated around the patient from different angles so that healthy tissue receives a much lower dose from each direction, while the tumour receives a concentrated combined dose. This reduces damage to surrounding tissue.
• Sterilisation: gamma rays are used to kill bacteria on surgical instruments and on some foods (such as strawberries and spices). The food does not become radioactive.
Gamma emitters with short half-lives are used as medical tracers. Radiotherapy targets tumours with focused, high-energy beams. Gamma rays sterilise instruments and food without making them radioactive.
Industrial Uses of Radiation
• Thickness gauges: beta radiation is passed through materials such as paper or aluminium sheet during manufacturing. A detector measures the count rate on the other side. If the material is too thick, fewer beta particles get through and the count drops; the rollers adjust automatically to correct the thickness. Alpha cannot be used (stopped too easily); gamma would pass through all thicknesses without enough variation.
• Smoke alarms: contain a small alpha source (americium-241). Alpha particles ionise air in a chamber, creating a small electrical current. Smoke particles absorb the alpha radiation, reducing the current and triggering the alarm.
• Carbon dating: living organisms continuously take in carbon from the environment, maintaining a constant proportion of carbon-14 (a radioactive isotope). After death, no new carbon-14 is taken in and the proportion decreases as it decays. By measuring the remaining activity, scientists can estimate the age of organic samples.
For medical tracers: choose a gamma emitter (passes through tissue for external detection), with a short half-life (minimises patient exposure), and one that is biochemically similar to a substance the target organ naturally absorbs.
For industrial thickness gauges: choose a beta emitter with a long half-life (so the source lasts years without replacement and gives a stable count rate for comparison).
For smoke alarms: choose an alpha emitter (highly ionising to maintain the detection current) with a long half-life (so the device works reliably for many years without replacement). Americium-241 has a half-life of around 430 years.
Nuclear Fission
Nuclear fission occurs when a large, unstable nucleus — such as uranium-235 — is struck by a slow-moving neutron and splits into two smaller nuclei (called fission fragments), releasing a large amount of energy and two or three neutrons. These released neutrons can trigger further fission events in other nuclei, potentially creating a chain reaction.
In a nuclear power station, the chain reaction is controlled: control rods (made of boron, cadmium or hafnium) absorb excess neutrons to ensure each fission event on average triggers exactly one more, keeping the reaction stable. A separate component called the moderator (commonly graphite or water) slows the neutrons so that they are more likely to cause further fission events; slowing the neutrons is a different function from absorbing them. The energy released heats water to produce steam, which drives turbines connected to generators. No carbon dioxide is produced during fission, but the process generates highly radioactive waste that requires careful long-term storage.
Nuclear fission: a large nucleus (e.g. uranium-235) splits when hit by a neutron, releasing energy and more neutrons that can trigger further fissions. In power stations, control rods maintain a steady, controlled chain reaction.
Nuclear Fusion
Nuclear fusion occurs when two light nuclei (typically isotopes of hydrogen) collide with enough energy to overcome electrostatic repulsion and fuse together, forming a heavier nucleus and releasing a large amount of energy. Fusion releases more energy per kilogram of fuel than fission.
Fusion is the process that powers our Sun and all other stars. In stars, the enormous gravitational pressure at the core forces hydrogen nuclei together at extremely high temperatures and densities. The energy released by fusion in the Sun’s core travels outwards as radiation and eventually reaches Earth as light and heat.
Achieving controlled nuclear fusion on Earth as an energy source has proved extremely challenging. The fuel (plasma of hydrogen isotopes) must be kept at temperatures exceeding tens of millions of degrees Celsius, far hotter than the Sun’s core. No known material can contain such a plasma directly; experimental reactors use powerful magnetic fields (in tokamak designs) to contain the plasma away from the reactor walls. As of now, no commercial fusion power plant is operational, though research is ongoing.
Fission: splits heavy nuclei (uranium-235, plutonium-239); produces radioactive waste; controlled in existing nuclear power stations; risk of meltdown if cooling fails.
Fusion: joins light nuclei (hydrogen isotopes); produces far less long-lived radioactive waste; releases more energy per kilogram of fuel; requires extreme temperature and pressure; not yet commercially viable.
Both processes release far more energy per kilogram than burning fossil fuels, and neither produces carbon dioxide during generation.
Risk–Benefit Analysis
Any use of radioactive materials involves weighing benefits against risks. For medical tracers, the benefit (diagnosing a serious disease) outweighs the small radiation dose if the isotope is chosen carefully. For nuclear power, the benefit (large-scale electricity with low carbon emissions) must be weighed against the risks of accidents and the challenge of storing highly radioactive waste safely for thousands of years.
Responsible decision-making requires considering: the type and dose of radiation, the likely duration of exposure, whether the exposure is deliberate (medical) or accidental, and whether precautions can reduce risk. Where potential harm is serious, the precautionary principle suggests caution even if the risk is uncertain.