A scientist investigates the decay of a radioactive isotope. The table shows the total count rate measured by a detector at regular intervals:
| Time (hours) | Total count rate (counts per minute) |
|---|---|
| 0 | 620 |
| 3.0 | 320 |
| 6.0 | 170 |
| 9.0 | 95 |
The half-life of the radioactive isotope is known to be exactly 3.0 hours3.0\text{ hours}3.0 hours.
Why is the measured total count rate always greater than half of the previously measured value?
The radioactive decay of the source is a random process.
There is a constant level of background radiation present.
The detector's sensitivity increases as the source decays.
The source emits highly penetrating gamma radiation.
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.