Physics 6.29, 6.31 - 6.32 - Radiation safety
Ionisation can damage cells and change DNA. Choose precautions for patients and workers by tracing how radiation reaches tissue and whether radioactive material can spread.
How ionising radiation causes harm
Ionising radiation transfers energy to atoms and molecules in living cells. If it removes electrons, ions are formed and important molecules can be changed.
There are several possible outcomes for an affected cell:
- the damage is repaired, so the cell continues to work normally;
- the cell is damaged or killed; many damaged or dead cells can cause tissue damage;
- DNA is changed and the cell survives; this is a mutation, which can increase the chance of uncontrolled cell division and cancer.
The outcome is not certain for one cell or one exposure. In general, a larger radiation dose means more energy has been delivered to tissue, so the chance of harm is greater. The radiation type and the tissue exposed also affect the hazard.
Reducing radiation dose
Precautions should interrupt the route by which radiation or radioactive material reaches a person. For an external source, three principles are central: time, distance and shielding.
| Precaution | How it reduces risk |
|---|---|
| Reduce the time spent near a source | Less time exposed usually means a smaller dose. Plan the task before approaching the source. |
| Increase the distance from a source | Radiation spreads out, so dose rate generally falls with distance. Remote handling tools or tongs keep hands and the body farther away. |
| Put suitable shielding between the source and person | The shielding absorbs some radiation before it reaches tissue. The material and thickness must suit the radiation; penetrating gamma radiation needs substantial shielding such as thick lead or concrete. |
| Keep a source shielded when it is not in use | A labelled, secure container reduces exposure and prevents unauthorised handling. |
When a radioactive substance could escape as a powder, liquid or gas, preventing contamination is also essential. Use sealed sources where possible, contain unsealed material over a lined tray, wear suitable gloves and protective clothing, keep food and drink away, and follow monitored clean-up procedures after a spill. These controls reduce the chance that material reaches skin, clothes, the mouth, lungs or a wound.
Controlled areas, warning lights and trained procedures restrict who can approach a source. A personal dosimeter records the dose received so exposure can be reviewed and work changed if necessary. It monitors risk; it does not act as a shield.
Choose a precaution by asking what must be interrupted: radiation travelling from an external source, radioactive material spreading, or both.
Safety in medicine
Medical exposure is different from an accidental exposure because it is used for an intended benefit. The aim is not always zero radiation: an image must be clear enough to diagnose a condition, and radiotherapy must deliver an effective dose to its target. Safety therefore uses two linked decisions:
- Justify the exposure: use ionising radiation only when the expected medical benefit outweighs the radiation risk, and check that the required information is not already available.
- Optimise the dose: use the lowest dose that is reasonably practicable for the medical purpose. Select suitable settings, restrict the beam or treatment to the required region, and avoid preventable repeat exposures.
A patient may need one examination or course of treatment. Medical personnel may work near radiation sources repeatedly, so even small occupational exposures can add to their total dose. Depending on the procedure, staff can leave the room, stand behind a shielded screen, increase their distance, minimise the time nearby, wear suitable protective shielding and use personal dosimeters. Warning systems, interlocks and controlled access help prevent accidental exposure.
An X-ray beam irradiates a patient while the machine is on. It does not leave X-ray material behind and does not make the patient radioactive.
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