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.
44 exam-style questions on CIE IGCSE Physics 5.2.1 Background radiation and measuring count rate. Each one has a worked solution and a mark scheme showing where the marks go.