15.1 How ionising radiation damages tissue

Ionising radiation can remove electrons from atoms and molecules in cells. This can break chemical bonds, damage membranes and alter DNA. A sufficiently high dose can kill cells. Damage to genetic material may produce mutations, and some mutations can lead to uncontrolled cell division and cancer.

The outcome depends on absorbed dose, radiation type, exposure time, body region and whether the source is outside or inside the body. Rapidly dividing tissues are often particularly sensitive.

15.2 External and internal exposure

An external alpha source is usually stopped by the dead outer skin layer, but alpha-emitting contamination inhaled or swallowed is dangerous because energy is deposited intensely in living tissue. Gamma is a major external hazard because of its penetration.

Contamination means radioactive material is present on or inside an object or person and may continue irradiating until removed or decayed. Irradiation means radiation passes through an object; the object does not automatically become radioactive.

15.3 Reducing exposure time

Dose increases with time in a radiation field. Plan the task first, work efficiently, avoid unnecessary repetition and return the source to storage immediately. Training and remote preparation reduce the time spent close to a source.

Time reduction should not cause rushed unsafe handling. The goal is efficient, controlled work.

15.4 Increasing distance

Moving farther from a source reduces exposure because radiation spreads through a larger area and some is absorbed by air and surroundings. Use tongs, long-handled tools, remote controls and barriers to increase separation from living tissue.

Distance is especially important for penetrating radiation. Never hold a source simply to save time.

15.5 Shielding and storage

Use shielding matched to radiation: paper or a sealed container contains alpha; aluminium or plastic can reduce beta; thick lead or concrete reduces gamma. Beta shielding choices should consider that very dense materials can produce secondary radiation in advanced contexts, though the O Level focus is suitable absorption.

Radioactive sources are stored in labelled, secure, shielded containers. They are moved in holders, kept away from people and accounted for. Disposal follows regulations and depends on half-life and activity.

15.6 Risk, dose and benefit

Radiation risk cannot be described only as “safe” or “dangerous”. Natural background exposure is unavoidable, while medical exposure may provide major benefit. Safety aims to keep exposure as low as reasonably achievable while achieving the necessary purpose.

In an examination evaluation, identify the benefit, the possible tissue damage, and the precautions that reduce risk. Avoid implying that one detected count automatically causes cancer; risk is probabilistic and dose-dependent.

Worked examples

Practical focus

Examination guidance

Check your understanding

1. Name three possible effects of ionising radiation on living tissue.
2. How do tongs reduce dose?
3. What is the difference between irradiation and contamination?