An isotope of iodine decays by β−\beta^-β− emission. It takes 32 days for its activity to fall to 116\displaystyle \frac{1}{16}161 of its original value. What is the half-life of the isotope?
2 days2\text{ days}2 days
8 days8\text{ days}8 days
16 days16\text{ days}16 days
128 days128\text{ days}128 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.