Radiation Hazards & Uses

Background Radiation

• Radiation dose is measured in sieverts (Sv).
• Doses are usually small, so millisieverts (mSv) are used (1 Sv = 1000 mSv).
• Dose varies with location, altitude and occupation.
• Detected with a Geiger–Müller tube or photographic film.

Geiger–Müller tube

Counts each ionising event and displays the count rate (for example counts per second).

Photographic film

Darkens with exposure – used in dose badges worn by workers.

Irradiation vs Contamination

Irradiation

• Radiation passes through the body and deposits energy inside.
• Cannot be removed by washing.
• May cause delayed effects.

Contamination

• Radioactive particles are on the surface of a person or object.
• Can be removed by washing or wiping.
• The person or object is not radioactive once the material is removed.

Precautions

• Limit time of exposure.
• Increase distance (use remote-controlled arms).
• Use shielding (lead-lined boxes, concrete walls, protective suits, gloves).

Effects on Living Tissue

Ionising radiation knocks electrons off atoms in cells.

• Low dose → mutations → possible cancer.
• High dose → cells die → radiation sickness (vomiting, hair loss, tiredness).
• Beta and gamma are most dangerous outside the body.
• Alpha is most dangerous inside the body (strongly ionising, localised damage) – so contamination matters more than irradiation for alpha sources.

Uses of Radiation

Smoke alarms

An alpha source ionises air to complete a small current; smoke breaks the circuit.

Radiotherapy

High-dose gamma directed at tumours kills cancer cells.

Thickness gauging

Beta radiation monitors the thickness of metal sheets (alpha is absorbed; gamma passes through).

Medical tracers

For example iodine-123 for the thyroid. PET scans use gamma emitters with a short half-life so radiation in the patient quickly disappears – isotopes must be produced nearby.

Sterilisation

Gamma radiation kills bacteria on medical equipment and in food irradiation without heating.