A scientist measures the activity of a radioactive sample every 15 minutes. The table shows the readings:
Time / minActivity / Bq01200158503060045425603007521090150 \begin{array}{|c|c|} \hline \text{Time / min} & \text{Activity / Bq} \\ \hline 0 & 1200 \\ 15 & 850 \\ 30 & 600 \\ 45 & 425 \\ 60 & 300 \\ 75 & 210 \\ 90 & 150 \\ \hline \end{array} Time / min0153045607590Activity / Bq1200850600425300210150What is the half-life of the source?
15 min15\text{ min}15 min
30 min30\text{ min}30 min
45 min45\text{ min}45 min
60 min60\text{ min}60 min
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.