A tracer must have an activity of at least 80 MBq80\ \mathrm{MBq}80 MBq at the end of a 4-hour investigation. To limit later exposure, its activity must be no more than 10 MBq10\ \mathrm{MBq}10 MBq after 16 hours. It remains in the system, and its activity changes only by radioactive decay. Which source meets both conditions?
| Source | Initial activity in MBq | Half-life in hours |
|---|---|---|
| P | 160 | 2 |
| Q | 160 | 4 |
| R | 160 | 8 |
| S | 320 | 4 |
Source R
Source P
Source S
Source Q
97 exam-style questions on Edexcel GCSE Physics 6.5 Uses and dangers of radioactivity, covering 6.5.1 Uses of radioactivity, 6.5.2 Dangers of ionising radiation and precautions, 6.5.3 Half-life and radiation dangers, 6.5.4 Safety precautions for radiation exposure, and 6.5.5 Contamination and irradiation. Each one has a worked solution and a mark scheme showing where the marks go.