Contamination and irradiation (AQA GCSE Physics Combined Science): Revision Notes
Contamination and irradiation
When dealing with radioactive materials, you can be affected in two different ways: irradiation or contamination. These are completely different processes that students often mix up.
Students frequently confuse irradiation and contamination, but understanding the difference is crucial for radiation safety. The key distinction is whether the radioactive source comes into contact with your body or not.
What is irradiation?
Irradiation happens when ionising radiation from a radioactive source travels to your body from the outside. The key point is that the radioactive material itself doesn't enter your body - you're not breathing it in, eating it, or drinking it.
Think of irradiation like standing in sunlight. The sun's rays reach you, but the sun itself doesn't come into contact with your body. This analogy helps you remember that in irradiation, the radiation travels to you, but the source stays separate.
Important facts about irradiation:
Key Facts About Irradiation:
- The radiation comes from an external source (outside your body)
- You don't become radioactive yourself
- Alpha particles are unlikely to be harmful during irradiation because they have a very short range in air (about 5 cm) and can't reach through your skin
- Gamma rays, beta particles, and X-rays can cause irradiation because they can travel further and penetrate the body
- When ionising radiation reaches body cells, it may damage or kill them
What is contamination?
Contamination is the unwanted presence of radioactive material on or inside your body or other objects. This means the actual radioactive source comes into direct contact with you.
The danger from contamination depends on what type of radioactive atoms are involved and how they decay.
Two types of contamination:
External contamination:
- Radioactive materials come into contact with your hair, skin, or clothing
- The radioactive source is on the outside of your body
- Can often be washed off
Internal contamination:
- A radioactive source is eaten or drunk
- The radioactive material gets inside your body
- Some foods like nuts, plants, and fruits can have low levels of radioactivity from radioactive minerals they're exposed to during growth
- Much harder to remove from the body
Key differences
The Main Difference:
- Irradiation: You're exposed to radiation, but the radioactive source stays separate from you
- Contamination: The radioactive source actually comes into contact with your skin or gets inside your body
With contamination, the radioactive material can continue to emit radiation while it's in contact with you. With irradiation, when you move away from the source, the exposure stops.
Examples to help you identify each type
Irradiation Examples:
- Having an X-ray to check for broken bones
- Being exposed to cosmic rays from the sun
- Standing near a radioactive source (but not touching it)
External Contamination Examples:
- Radioactive dust landing on your skin
- Getting radioactive material on your clothes
Internal Contamination Examples:
- Eating food that contains radioactive strontium-90
- Drinking water contaminated with radioactive materials
Summary
Key Points to Remember:
- Irradiation = radiation from outside reaches you, but you don't touch the radioactive source
- Contamination = radioactive material actually contacts your body (external) or gets inside you (internal)
- Irradiation doesn't make you radioactive, but contamination means radioactive material is present on or in your body
- Alpha particles are mainly dangerous through contamination, not irradiation
- You can often wash off external contamination, but internal contamination is much harder to remove