Sterilisation Principle: Irradiation involves exposing objects to high-energy gamma radiation to kill bacteria, viruses, and other microorganisms. This is a 'cold' process, meaning it does not require heat, which is vital for sterilising heat-sensitive medical tools like plastic syringes.
Food Preservation: By irradiating food, the microorganisms that cause spoilage and food poisoning are destroyed without changing the food's temperature or nutritional value. This process significantly extends the shelf life of fresh produce and prevents the growth of mould.
Safety Note: It is critical to understand that irradiation does not make the object radioactive. The object is exposed to the energy of the waves (gamma rays), but it never comes into contact with the radioactive source itself.
| Application | Radiation Type | Reason for Choice |
|---|---|---|
| Smoke Detectors | Alpha () | High ionisation to create current; low penetration so smoke can block it. |
| Thickness Gauge | Beta () | Medium penetration; sensitive to changes in thickness of paper/foil. |
| Sterilisation | Gamma () | High penetration to reach all parts of a package; kills bacteria. |
| Medical Tracers | Gamma () | High penetration allows it to leave the body to be detected externally. |
Property-to-Use Mapping: When asked why a specific radiation is used, always link the physical property (penetration or ionisation) to the specific requirement of the task. For example, 'Beta is used for paper thickness because alpha would be stopped and gamma would pass through unaffected.'
The 'Radioactive' Fallacy: A common exam trap is suggesting that irradiated food becomes radioactive. Always clarify that irradiation is exposure to waves, whereas contamination is the physical presence of radioactive atoms.
Safety Logic: If a question asks about medical tracers, remember that the isotope must have a short half-life to minimize the dose to the patient, but long enough to complete the medical procedure.
