A sample of a radioactive isotope has an initial emission rate of 160 counts per second160\text{ counts per second}160 counts per second and a half-life of 6 hours6\text{ hours}6 hours. How long will it take for the emission rate to fall to 20 counts per second20\text{ counts per second}20 counts per second?
6 hours6\text{ hours}6 hours
12 hours12\text{ hours}12 hours
18 hours18\text{ hours}18 hours
24 hours24\text{ hours}24 hours
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.