A food manufacturer uses gamma rays to sterilise packaged food before it is sent to supermarkets. Explain why gamma radiation is suitable for this purpose, and why alpha radiation would not be suitable.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Packaged food can be exposed to ionising radiation after sealing to extend its shelf life and make it safe to eat. The radiation must be able to pass through the packaging and reach the food inside.
Model answer (5 marks)
Gamma rays are highly penetrating electromagnetic radiation and can pass through the packaging material to reach the food inside.
Gamma rays transfer sufficient energy to the bacterial cells, breaking chemical bonds and destroying DNA, thereby sterilising the food.
Because the food is irradiated rather than contaminated, it does not become radioactive.
Alpha particles are weakly penetrating; a few centimetres of air or thin packaging stops them.
Thus alpha radiation would not reach the bacteria inside the packaging and could not sterilise the food.
Gamma rays transfer sufficient energy to the bacterial cells, breaking chemical bonds and destroying DNA, thereby sterilising the food.
Because the food is irradiated rather than contaminated, it does not become radioactive.
Alpha particles are weakly penetrating; a few centimetres of air or thin packaging stops them.
Thus alpha radiation would not reach the bacteria inside the packaging and could not sterilise the food.
Examiner tips
- Use the exact terms ‘highly penetrating’ and ‘transfer energy to kill bacteria’.
- Explain both the penetration and the biological effect of gamma rays.
- Mention that the food is not contaminated with radioactivity.
- Show why alpha particles cannot penetrate the packaging.
Mark scheme (5 marks)
- Gamma rays are highly penetrating / can pass through the packaging to reach the food inside
- Gamma rays transfer energy to / kill bacteria inside the food / sterilise the food
- The food is irradiated (not contaminated) so it does not become radioactive itself
- Alpha particles are weakly penetrating / stopped by a few centimetres of air or thin packaging
- Therefore alpha radiation would not reach the food / bacteria inside the packaging and could not sterilise it
Key terms in this question
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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