When a radioactive isotope is set up close to a radiation detector, a count rate of 64 000 counts/s64\,000\text{ counts/s}64000 counts/s is obtained. The table shows the count rate from the isotope over a three-year period:
| Time / years | Count rate / counts/s\text{counts/s}counts/s |
|---|---|
| 0 | 64 00064\,00064000 |
| 1 | 48 00048\,00048000 |
| 2 | 36 00036\,00036000 |
| 3 | 27 00027\,00027000 |
What is the half-life of the isotope?
less than 1 year
more than 1 year but less than 2 years
more than 2 years but less than 3 years
more than 3 years
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.