A technician works in a hospital where radioactive sources are used regularly. Explain why the technician wears a photographic film badge and why it is important that background radiation is measured at the start of each working day.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Radioactive sources are used in hospitals for a range of diagnostic and treatment purposes. Workers who handle these sources must follow strict safety procedures to monitor their exposure to radiation.
Model answer (5 marks)
A photographic film badge is worn because the film is sensitive to ionising radiation; as the technician is exposed, the film darkens proportionally to the amount of radiation absorbed, giving a record of the total dose received over time.
It is important to measure background radiation at the start of each working day because background radiation is always present from natural and man‑made sources. The readings from the badge must have this background subtracted to determine the true exposure from the hospital’s radioactive sources. Since background radiation can vary from day to day or at different times, measuring it each day ensures an accurate correction and reliable dose assessment.
It is important to measure background radiation at the start of each working day because background radiation is always present from natural and man‑made sources. The readings from the badge must have this background subtracted to determine the true exposure from the hospital’s radioactive sources. Since background radiation can vary from day to day or at different times, measuring it each day ensures an accurate correction and reliable dose assessment.
Examiner tips
- Use the phrase ‘photographic film badge’ and explain darkening as a dose indicator.
- Mention that background radiation must be subtracted to obtain the true source dose.
- Highlight that background varies daily, justifying daily measurement.
Common mistakes
- Confusing the badge with a personal dosimeter that measures dose rate instead of total dose.
- Failing to state that background must be subtracted from the badge reading.
- Overlooking the daily variation of background radiation.
Mark scheme (5 marks)
- The photographic film absorbs radiation and goes darker / the greater the radiation absorbed, the darker the film becomes
- The badge allows monitoring of the total radiation exposure / dose received by the technician over time
- Background radiation is present all around us from natural and/or man-made sources
- Background radiation must be subtracted from / accounted for in readings to find the true count rate from the radioactive source alone
- Background radiation can vary day to day / at different times, so it must be measured each day to ensure an accurate correction is made
Key terms in this question
photographic film badge · background radiation · radioactive source
Related
- All Edexcel A-Level Physics (9PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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