The count rate due to a sample of a radioactive isotope is measured for 80 minutes and recorded in the table below:
| Time (minutes) | Count rate (counts / second) |
|---|---|
| 0 | 640 |
| 20 | 450 |
| 40 | 320 |
| 60 | 225 |
| 80 | 160 |
What is the half-life of the isotope?
20 minutes20\text{ minutes}20 minutes
40 minutes40\text{ minutes}40 minutes
60 minutes60\text{ minutes}60 minutes
80 minutes80\text{ minutes}80 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.