A student measures the count rate from a radioactive source in a laboratory. The results are recorded in the table below:
| Time / minutes | Count rate / (counts / s) |
|---|---|
| 0 | 135 |
| 1.0 | 110 |
| 2.0 | 91 |
| 3.0 | 75 |
| 4.0 | 63 |
The average background radiation in the laboratory is 15 counts/s15\text{ counts/s}15 counts/s.
What is the half-life of the source?
1.0 minute1.0\text{ minute}1.0 minute
2.0 minutes2.0\text{ minutes}2.0 minutes
3.0 minutes3.0\text{ minutes}3.0 minutes
4.0 minutes4.0\text{ minutes}4.0 minutes
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.