CAIE IGCSE Physics half-life calculations
Practise defining half-life and using repeated halving to predict atoms, mass or count rate over minutes, days or years.
- Syllabus
- 2026–2028
- Course
- Physics 0625
Exam points
- define half-life as the time for nuclei or decay rate in a sample to halve
- calculate elapsed time from remaining atoms, mass or count rate after repeated halving
- explain why very short or very long half-lives can be unsuitable for a tracer
5.2.4.1—Half-life as the time for half the question 1
[Maximum number: 3]
A radiation detector is set up in a laboratory where there are no radioactive samples.
On six separate occasions, the detector is switched on for 1.0 minute and the background count is recorded. The counts are:
232725242025
A sample containing only one radioactive isotope is brought into the laboratory. The half-life of the isotope is 15 hours.
The sample is placed near to the radiation detector in this laboratory. The detector is switched on and, after 1.0 minute, a count of 440 is recorded.
The sample is left next to the detector and the experiment is repeated 45 hours later.
The detector is switched on for 1.0 minute.
Predict the reading for the count obtained on this occasion.
reading
440-24 or 416 or 52 or 55 or 79 or 3 (half-lives) or 45 / 15 or 1/23 or 1 / 8
1/23 or 1 / 8 or 52 or 55 or 79
76 (counts)
C1
C1
A1
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