Radioactivity and Particles
5 marks · NormalA hospital uses a radioactive isotope that emits gamma radiation to sterilise medical equipment and measure the thickness of plastic film. The table shows typical penetrating and ionising properties of the three main types of radiation.
| Radiation | Penetrating Power | Ionising Power |
|---|---|---|
| Alpha | Low (stopped by paper) | High |
| Beta | Medium (stopped by aluminium) | Medium |
| Gamma | Very high (stopped by thick lead) | Low |
Explain, using information from the table, why gamma radiation is suitable for both sterilising equipment and measuring the thickness of plastic film.
The activity of the radioactive source is measured in a laboratory. A scientist records a value of 5000 Bq at the start. State what the unit becquerel measures and convert the recorded activity to kBq.
Describe one safety precaution that workers should follow when handling radioactive sources.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) — · must show penetrating power allows sterilisation, penetration through thin film but low ionising for safety
(b) The becquerel is the number of decays per second. 5000 Bq is 5 kBq. · must show definition of Bq, conversion (5000 Bq = 5 kBq)
(c) Store radioactive sources in lead-lined containers / use tongs to handle. · must show one valid safety step
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · States that gamma rays are highly penetrating, so useful to sterilise or measure thickness.
M2 (a) · 1 mark · Mentions low ionising power or safety, or ability to pass through material for thickness measurement.
B1 (b) · 1 mark · Defines becquerel as decays per second.
A1 (b) · 1 mark · Correct conversion to 5 kBq.
B2 (c) · 1 mark · States a valid safety precaution (storage, handling, shielding).
Worked solution
(a) Gamma rays have very high penetrating power, so they can pass through the equipment or film, making them suitable for sterilising inside packaging or measuring thickness since the rays are not easily blocked. Their low ionising power means they are less likely to damage material or harm workers nearby.
(b) The becquerel (Bq) measures the number of decays per second. 5000 Bq divided by 1000 gives 5 kBq.
(c) Radioactive sources should be stored in lead-lined containers to reduce exposure.