The half-life for plutonium-239 is 24 000 years24\,000\text{ years}24000 years.
A sample of plutonium-239 produces 640 counts/s640\text{ counts/s}640 counts/s.
How long will it take for the count rate to drop to 80 counts/s80\text{ counts/s}80 counts/s?
48 000 years48\,000\text{ years}48000 years
72 000 years72\,000\text{ years}72000 years
96 000 years96\,000\text{ years}96000 years
192 000 years192\,000\text{ years}192000 years
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.