The half-life of a radioactive isotope is 5.0 days5.0\text{ days}5.0 days.
A sample of this material contains 80 million80\text{ million}80 million radioactive nuclei.
How many of these radioactive nuclei remain undecayed after 15 days15\text{ days}15 days?
5.0 million5.0\text{ million}5.0 million
10 million10\text{ million}10 million
20 million20\text{ million}20 million
40 million40\text{ million}40 million
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.