Everything on the GCSE Physics Radiation Hazards & Uses poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
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. Radiation is detected using a Geiger-Muller tube (counts each ionising event) or photographic film (darkens with exposure, used in dose badges).
Background radiation comes from both natural and man-made sources:
| Natural sources | Man-made sources |
|---|---|
| Radon gas | Medical |
| Rocks / soil | Nuclear fallout |
| Cosmic rays | Nuclear waste (tiny proportion) |
| Food |
Irradiation vs contamination
Irradiation - radiation passes through the body and deposits energy inside. It cannot be removed by washing, and may cause delayed effects. The person or object is not itself radioactive.
Contamination - radioactive particles are on the surface of the body or object. They can be removed by washing or wiping. The person or object is not inherently radioactive - the particles are the source.
Precautions
- Limit time of exposure - the less time spent near a source, the lower the dose received.
- Increase distance - use remote-controlled arms to handle sources from a distance.
- Use shielding - lead-lined boxes, concrete walls, protective suits and gloves all reduce exposure.
Effects on living tissue
Ionising radiation knocks electrons off atoms in cells.
- Low dose - can cause mutations; these may lead to cancer.
- High dose - kills cells directly, causing radiation sickness (symptoms include vomiting, hair loss and tiredness).
- Beta and gamma are most dangerous outside the body.
- Alpha is most dangerous inside the body (strongly ionising, localised damage), so contamination is a greater concern than irradiation for alpha sources.
Uses of radiation
Smoke alarms
- An alpha source ionises the air to complete a small current; smoke breaks the current and triggers the alarm.
Radiotherapy
- High-dose gamma radiation is directed at tumours.
- Kills cancer cells.
Thickness gauging of metal sheets
- Beta is absorbed by the sheet; gamma passes straight through. The amount of beta detected indicates the sheet's thickness.
Medical tracers
- For example, iodine-123 is taken up by the thyroid.
- PET scans use gamma with a short half-life so that the radioactive tracer quickly disappears from the patient's body.
- PET isotopes must be produced nearby because of their short half-life.
Sterilising medical equipment and food irradiation
- Gamma kills bacteria without heating, so instruments stay intact and food quality is preserved.