The half-life for uranium-234 is 245,000 years245{,}000\text{ years}245,000 years.
A sample of uranium-234 produces 960 counts/s960\text{ counts/s}960 counts/s.
How long will it take for the count rate to drop to 120 counts/s120\text{ counts/s}120 counts/s?
490,000 years490{,}000\text{ years}490,000 years
735,000 years735{,}000\text{ years}735,000 years
980,000 years980{,}000\text{ years}980,000 years
1,960,000 years1{,}960{,}000\text{ years}1,960,000 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.