A student is investigating how the radiation from a radioactive sample changes with time. The table below shows the recorded count-rates at regular intervals:
| Time / min | Count-rate / counts per minute |
|---|---|
| 0 | 340 |
| 3 | 180 |
| 6 | 100 |
| 9 | 60 |
| 12 | 40 |
The half-life of the radioactive isotope is known to be exactly 3 minutes.
Why is the measured count-rate always higher than half of the previously recorded value?
The emissions from the radioactive source occur randomly over time.
The detector is placed too close to the radioactive source.
There is background radiation present in the environment.
The isotope in the source is undergoing active radioactive decay.
144 exam-style questions on CIE IGCSE Physics 5.2.4a Half-life. Each one has a worked solution and a mark scheme showing where the marks go.