A scientist measures the count rate of a radioactive sample in a laboratory over a period of 15 days.
The background radiation count rate in the laboratory remains constant at 30 counts per minute.
The table shows the scientist's results before the background radiation count rate is taken into account:
| Time / days | Count rate / counts per minute |
|---|---|
| 0 | 190 |
| 3 | 151 |
| 6 | 122 |
| 9 | 100 |
| 12 | 83 |
| 15 | 70 |
In which range does the half-life of the radioactive isotope lie?
between 3 and 6 days
between 6 and 9 days
between 9 and 12 days
more than 15 days
484 exam-style questions on CIE IGCSE Physics 5.2 Radioactivity, covering 5.2.1 Background radiation and measuring count rate, 5.2.2a Alpha, beta and gamma emission, 5.2.2b Deflection and ionising effects of nuclear radiation, 5.2.3a Radioactive decay, 5.2.3b Effects of decay on the nucleus and decay equations, 5.2.4a Half-life, 5.2.4b Choosing isotopes for applications, and 5.2.5 Effects of ionising radiation and safety precautions. Each one has a worked solution and a mark scheme showing where the marks go.