A student investigates how the radiation from a radioactive source changes over time. The table below shows the results from the detector used by the student:
| Time / minutes | Measured count rate / counts per minute |
|---|---|
| 0 | 500 |
| 3.0 | 260 |
| 6.0 | 140 |
| 9.0 | 80 |
The half-life of the source is known to be exactly 3.03.03.0 minutes.
Explain why the measured count rate after each 3.03.03.0-minute interval is always greater than half of the previous measured count rate, and calculate the constant background radiation count rate.
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.