Learning outcomes
- Distinguish heating and ionising hazards.
- Describe damage from ultraviolet, X-rays and gamma rays.
- Relate risk to intensity and exposure time.
- Suggest suitable protection methods.
15.1 Exposure and dose
Radiation risk depends on the energy absorbed by tissue. Greater intensity, longer exposure time and shorter distance from a source usually increase dose. Safety therefore uses three broad principles: reduce time, increase distance and use suitable shielding.
Not every electromagnetic wave is equally hazardous in the same way. Low-frequency radiation mainly produces heating at high intensities, while sufficiently high-frequency radiation can ionise atoms and damage DNA.
15.2 Heating effects
Excessive exposure to microwaves and infrared can heat soft tissue and cause burns. Microwaves can penetrate below the surface, while infrared is absorbed strongly near the skin. Equipment is designed with enclosures, interlocks and exposure limits to prevent dangerous leakage.
Visible light of very high intensity, including lasers, can damage the retina because the eye focuses it onto a small area. Although the syllabus statement highlights heating and ionising effects, this is a useful application of intensity and tissue absorption.
15.3 Ultraviolet damage
Ultraviolet can damage skin cells, increasing the risk of skin cancer. It can also damage the eye and contribute to cataracts. Protection includes clothing, shade, suitable sunscreen and UV-blocking eyewear.
UV exposure can have beneficial controlled uses, such as sterilisation, but the source should be enclosed and users protected. The existence of an application does not remove the hazard.
15.4 X-rays and gamma rays
X-rays and gamma rays are ionising. They can remove electrons from atoms, damage molecules and cause cell mutations. High doses can kill cells; this is exploited in cancer treatment, but unintended exposure can raise cancer risk.
Protection may include lead, thick concrete, remote handling, monitoring badges and restricting exposure time. Medical imaging uses the lowest dose that provides the required information, with shielding for unaffected body regions when appropriate.
15.5 Balancing benefits and risks
Physics questions may ask for evaluation. A complete answer recognises that radiation can diagnose disease, treat cancer, sterilise equipment or provide communication, while exposure must be controlled. The conclusion should depend on dose, necessity and available alternatives.
Avoid claims that any exposure automatically causes cancer. Risk is probabilistic and increases with dose. Equally, do not claim that “safe limits” make the radiation harmless; they reduce risk to an accepted level.
Worked examples
Reducing dose
A worker halves the time near a source and doubles the distance. Both changes reduce dose; the exact distance relationship depends on geometry, but the qualitative safety improvement is clear.
Classifying effects
A microwave oven leak mainly poses a heating hazard. Unshielded X-rays pose an ionising hazard that may cause mutations.
Practical focus
Investigation
Analyse safety features of a medical X-ray room or microwave oven from diagrams: shielding, warning lights, interlocks, distance and exposure-time controls. Explain the role of each feature.
Examination guidance
- Use “ionising” for UV, X-ray and gamma effects specified by the syllabus.
- Name the biological outcome: skin cancer, cataracts, mutation, cell death or cancer.
- Give a protection method suited to the radiation rather than saying only “wear protection”.
Check your understanding
- What damage can excessive UV cause?
- Why is lead used around X-ray sources?
- State two ways to reduce dose.
Answers
- Skin cancer and cataracts.
- It absorbs X-rays strongly and reduces transmitted intensity.
- Reduce exposure time, increase distance, or use appropriate shielding.
