Contamination & Irradiation
Shielding (Irradiation Protection): To prevent irradiation, high-density materials like lead or thick concrete are placed between the source and the observer. These materials absorb the energy of the radiation before it reaches living tissue.
Barriers & Hygiene (Contamination Protection): To prevent contamination, workers wear airtight suits, gloves, and masks to ensure radioactive dust or gas is not inhaled, ingested, or stuck to the skin. Using tongs ensures a safe distance from the source.
Monitoring: Devices like dosemeters or film badges are worn to track the cumulative amount of radiation a person has been exposed to over time, ensuring they stay within safe legal limits.
| Feature | Irradiation | Contamination |
|---|---|---|
| Definition | Exposure to radiation from an external source | Radioactive material is physically on/in the object |
| Radioactivity | The object does NOT become radioactive | The object BECOMES radioactive |
| Prevention | Use shielding (lead) and distance | Use protective clothing and safe handling |
| Duration | Stops when the source is removed | Continues until material is removed or decays |
| Intent | Often deliberate (e.g., sterilization) | Almost always accidental (e.g., leaks) |
Identify the Source Location: Always check if the radioactive source is described as being 'outside' the body or 'on/inside' the body. This is the fastest way to distinguish between irradiation and contamination.
The 'Glow' Fallacy: Never state that an irradiated object (like medical equipment or food) becomes radioactive. This is a common mistake that loses marks; only contamination makes an object a source of radiation.
Half-Life Logic: Remember that sources with short half-lives pose a higher irradiation risk due to high initial activity, while sources with long half-lives pose a long-term contamination risk as they remain active for centuries.
Confusing Alpha Hazards: Students often think alpha is 'safe' because it can't penetrate skin. While true for irradiation, alpha is the most dangerous form of contamination if ingested because its high ionizing power causes massive damage to internal cells.
Shielding vs. Removal: You can block irradiation with a lead screen, but you cannot 'block' radiation from a contaminated person with a screen; you must physically remove the radioactive material (decontamination).