A sample of a radioactive isotope has an initial rate of emission of 240 counts per minute240\text{ counts per minute}240 counts per minute and a half-life of 6 days6\text{ days}6 days.
How long will it take for the rate of emission to fall to 30 counts per minute30\text{ counts per minute}30 counts per minute?
6 days6\text{ days}6 days
12 days12\text{ days}12 days
18 days18\text{ days}18 days
24 days24\text{ days}24 days
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.