Radiation: Risks and Benefits
Radiation All Around Us
Radiation is part of daily life. We are constantly exposed to background radiation from rocks (particularly granite), from cosmic rays from space, from radon gas in the air, from food and drink, and from medical procedures. This background dose varies by location — living in Cornwall exposes you to more radon than living in London, because granite rock releases more of this naturally occurring radioactive gas.
Not all radiation is the same. The key distinction for understanding risk is whether the radiation is ionising or non-ionising. Ionising radiation carries enough energy to knock electrons away from atoms, turning them into ions. This can damage or destroy cells and, if it alters DNA, may trigger cancer. Non-ionising radiation does not have enough energy to ionise atoms, though it can still cause harm at high doses.
Ionising radiation: alpha (\(\alpha\)), beta (\(\beta\)) and gamma (\(\gamma\)) from radioactive materials, plus X-rays and high-energy ultraviolet. Non-ionising: visible light, infrared, microwaves, radio waves. Ionising radiation is far more dangerous because it can damage DNA directly.
Types of Ionising Radiation
Alpha, beta and gamma differ in penetrating power and ionising ability — and these differences determine both their hazards and their uses:
• Alpha (\(\alpha\)): a helium nucleus (2 protons + 2 neutrons). Strongly ionising because its large charge and mass interact intensely with matter. Stopped by a few centimetres of air or a sheet of paper. Cannot penetrate skin, so an external alpha source poses little risk to internal organs — but if an alpha-emitting substance is inhaled or swallowed, the radiation delivers its full energy to sensitive tissue close by.
• Beta (\(\beta\)): a fast-moving electron. Moderately ionising. Penetrates paper but stopped by a few millimetres of aluminium. Can penetrate a short distance into body tissue.
• Gamma (\(\gamma\)): a high-energy electromagnetic wave. Weakly ionising but highly penetrating — passes through the body and is only significantly absorbed by dense lead or thick concrete. This penetrating power makes it useful for both medical imaging and radiotherapy, but means external gamma sources are hazardous from a distance.
• X-rays: also electromagnetic, similar to gamma but produced by electron transitions in machines rather than by nuclear decay. Similar penetrating power to gamma.
How Radiation Harms the Body
Ionising radiation harms cells in two main ways. At high doses, it kills cells directly — this is what causes radiation sickness and burns in severe accidents. At lower doses, it can alter DNA without killing the cell. A mutated cell may then divide uncontrollably, potentially causing cancer. The radiation dose received is the key factor: the higher the dose and the longer the exposure time, the greater the risk. This is why medical imaging doses are kept as low as possible while still providing a useful image.
It is important to distinguish between contamination and irradiation. Contamination means a radioactive substance is on or inside the body, continuing to deliver radiation that cannot be stopped simply by moving away. Irradiation means being exposed to radiation from an external source; once the source is removed the exposure stops and the person does not become radioactive. Contamination is generally considered more dangerous because the exposure is continuous and the substance may be inside the body where even alpha particles can reach sensitive tissue.
Contamination (radioactive material in/on the body) is more dangerous than irradiation (external exposure) because the source continues to deliver radiation internally, even from alpha particles that cannot penetrate skin from outside.
Beneficial Uses of Radiation
The same properties that make radiation hazardous also make it medically and industrially useful. Every use involves a risk–benefit judgement that depends on the specific situation.
X-rays in medical imaging: X-rays penetrate soft tissue but are absorbed by denser material like bone and metal. A dental X-ray exposes the patient to a fraction of the dose of a chest X-ray, and a chest X-ray delivers a dose roughly equivalent to a few days of background radiation. The benefit — diagnosing broken bones, tooth decay, or tumours — is very likely to outweigh the small additional risk for most patients. Pregnant women and children are treated more cautiously because their cells are dividing rapidly and are more vulnerable.
Radiotherapy: high doses of gamma rays or focused X-rays (or sometimes beta-emitting implants) target cancerous tumours. The beam is directed from several angles so that healthy surrounding tissue receives only a fraction of the dose that the tumour receives. The benefit — destroying a life-threatening cancer — must be weighed against the risk of damage to healthy tissue and the small risk of triggering a secondary cancer years later. For most cancer patients, the benefit substantially outweighs the risk.
Radioactive tracers: a gamma-emitting radioactive substance with a short half-life (such as technetium-99m, which has a half-life of around 6 hours) is introduced into the body. Because gamma rays penetrate the body, their path can be tracked externally, allowing doctors to image organ function. The short half-life means the patient’s dose is minimised — the isotope decays to negligible levels within a day.
Sterilisation: gamma rays kill bacteria on medical equipment and can be used to extend the shelf life of food. The food does not become radioactive — gamma radiation passes through it without leaving any radioactive material behind.
Smoke detectors are a familiar everyday use. They contain a tiny source of alpha radiation (americium-241). Alpha particles ionise air molecules, creating a small electrical current. Smoke particles disrupt this current, triggering the alarm. Because the alpha source is sealed inside the detector and alpha particles cannot penetrate the casing, the risk to the user is negligible — a clear example where the benefit (early warning of fires) substantially outweighs the risk.
Risk–Benefit Reasoning in Practice
Good risk–benefit reasoning requires thinking about the specific context, not just listing generic risks and benefits. For a given scenario, consider:
• Who is exposed? A 70-year-old patient with cancer faces a very different calculus from a healthy 20-year-old having an elective scan.
• What is the dose? Background radiation is always present; a procedure that adds a small fraction to this carries less additional risk than one that significantly increases total exposure.
• What is the alternative? If refusing a scan means a treatable cancer goes undetected, the risk of the scan is almost certainly worth taking.
• What is the uncertainty? At very low doses, cancer risk is hard to measure precisely because the effect is too small to detect against background rates. This uncertainty cuts both ways — it does not mean the risk is zero or that it is large.
Extended-response questions expect you to evaluate a named scenario using this kind of reasoning — not just to list facts about radiation types.