An accident in a research laboratory released a quantity of the radioactive isotope cobalt-60. Twenty-one years after the accident, the quantity of cobalt-60 present will be 6.25% of its original level.
What is the half-life of cobalt-60?
4.20 years4.20\text{ years}4.20 years
5.25 years5.25\text{ years}5.25 years
7.00 years7.00\text{ years}7.00 years
10.5 years10.5\text{ years}10.5 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.