Uses and Hazards of Radiation

Nuclear radiation is genuinely double-edged. The very property that makes it dangerous — its ability to ionise atoms and so damage living cells — is also what makes it enormously useful, from diagnosing illness and treating cancer to sterilising equipment and dating ancient remains. Using radiation safely means understanding both sides: knowing how it can harm us and how to protect against it, and knowing how to choose the right isotope for each job. This lesson, part of Topic P6 (Radioactivity) of OCR Gateway Science A, draws the crucial distinction between irradiation and contamination, surveys the main uses of radiation, sets out the hazards and the safety measures, and shows how the half-life and type of radiation determine which isotope is suitable for a given task.

By the end of this lesson you should be able to distinguish irradiation from contamination, describe the main uses of radiation, explain the hazards of radiation and the precautions taken, and choose a suitable isotope (by half-life and radiation type) for a given use.

---

Irradiation Versus Contamination

This distinction is one of the most heavily tested ideas in the whole topic, and the two terms are easy to confuse, so it is worth getting absolutely clear.

• Irradiation is being exposed to radiation from a source that is outside your body. The source itself does not touch you or get onto or into you — you are simply in the path of the radiation it emits. Once you move away from the source (or it is removed), the irradiation stops. Irradiation does not make you radioactive.
• Contamination is getting the radioactive material itself onto your skin, your clothing, or inside your body (by swallowing, breathing it in, or through a wound). Because the radioactive atoms are now on or in you, they keep on irradiating you from close range for as long as they remain — and you can spread them to others. Contamination is hard to remove and can continue for a long time.

The link to the types of radiation is important here. For irradiation from outside the body, the most dangerous radiation is the most penetrating — gamma (and beta) — because alpha is stopped by skin and clothing and never gets in. But for contamination, when the source is inside you, the most dangerous radiation is the most ionising — alpha — because it deposits all its energy in a tiny region of nearby tissue and cannot escape. This neat reversal is a favourite exam point.

Exam Tip: Irradiation = exposure to radiation from an outside source (stops when you move away; does not make you radioactive). Contamination = the radioactive material itself gets onto or into you (keeps irradiating you from close range). Outside the body gamma is most hazardous; inside the body alpha is most hazardous.

---

Uses of Radiation

Radiation has a wide range of practical uses, each exploiting a particular type of radiation and half-life.

Medical uses:

• Medical tracers. A small amount of a gamma-emitting isotope (with a short half-life) is injected or swallowed; its gamma rays pass out of the body and are detected to image how an organ, such as the kidney or thyroid, is working. Gamma is used because it escapes the body; a short half-life means the activity soon falls so the patient is not exposed for long.
• Radiotherapy. High-energy gamma rays (or beams of radiation) are aimed at a cancer tumour to kill the cancer cells. Beams are directed from several angles, or a source is placed near the tumour, to give the tumour a high dose while sparing healthy tissue as far as possible.
• Sterilising medical equipment. Surgical instruments are exposed to intense gamma radiation to kill bacteria and microbes, sterilising them without heat — useful for plastic items that would melt if boiled.

Other uses:

• Sterilising/preserving food. Gamma radiation kills microbes on food, making it keep longer, without making the food radioactive.
• Smoke detectors. A weak alpha source ionises the air inside the detector, allowing a tiny current to flow; smoke absorbs the alpha particles, the current drops, and the alarm sounds. Alpha is ideal because it is stopped easily (so it is safe at a distance) yet strongly ionising.
• Thickness/level gauges. A beta source on one side of a sheet (of paper, metal foil or plastic) and a detector on the other side measure the thickness: if the sheet gets thicker, fewer beta particles get through, so the detector reading falls and rollers adjust the thickness. Beta is used because alpha would be stopped by the sheet entirely and gamma would pass through almost unchanged regardless of thickness.
• Radioactive (carbon) dating. Living things take in carbon-14 (a beta emitter, half-life about $5730$5730 years) while alive; when they die, no more is taken in and the carbon-14 slowly decays. By comparing the activity of an old sample with that of a living one, the age can be estimated. Very old rocks are dated using isotopes with much longer half-lives (such as uranium).

Exam Tip: Match the radiation type to the job: alpha → smoke detectors (easily stopped, strongly ionising); beta → thickness gauges (partly absorbed, sensitive to thickness); gamma → tracers, radiotherapy, sterilising (penetrating, escapes the body or reaches deep tissue/microbes).

---

Hazards of Radiation and Radiation Dose

The hazard of nuclear radiation comes from its ionising ability. When radiation passes through living tissue, it ionises atoms in the cells, which can damage or kill cells or change (mutate) the DNA. A high dose can cause radiation sickness and kill cells outright; a lower dose can cause mutations that may, much later, lead to cancer.

The amount of radiation a person receives is described by their radiation dose, measured in sieverts (Sv) (or, more usually, millisieverts, mSv). The dose takes account of both the amount of radiation absorbed and how harmful that particular type of radiation is to the body. A higher dose means a greater risk of harm. Everyone receives a small dose from background radiation each year; the concern is with additional exposure on top of that.

Exam Tip: Radiation harms us because it ionises atoms in cells, which can kill cells (high dose) or mutate DNA and cause cancer (lower dose). Radiation dose is measured in sieverts and reflects both how much radiation is absorbed and how damaging it is; higher dose = higher risk.

---

Safety: The ALARA Principle

Because there is no completely "safe" dose, the guiding rule for anyone working with radiation is to keep exposure As Low As Reasonably Achievable — the ALARA principle. In practice, exposure is reduced in three main ways:

• Shielding — putting an absorbing barrier between the person and the source. Dense materials such as lead and thick concrete absorb radiation; workers stand behind lead screens, sources are stored in lead-lined boxes, and lead aprons are worn during X-rays.
• Distance — staying as far from the source as possible. Radiation spreads out and weakens rapidly with distance, so handling sources with long tongs or remote tools, rather than bare hands, greatly reduces the dose.
• Time — keeping the time of exposure as short as possible. The less time spent near a source, the smaller the total dose received.