A radioactive isotope has a half-life of 15 days15\text{ days}15 days.
It initially emits radiation at a rate of 800 counts per second800\text{ counts per second}800 counts per second.
How long does it take for the rate of emission to fall to 100 counts per second100\text{ counts per second}100 counts per second?
5 days5\text{ days}5 days
30 days30\text{ days}30 days
45 days45\text{ days}45 days
120 days120\text{ days}120 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.