A radioactive isotope has a half-life of 6 hours6\text{ hours}6 hours.
A detector close to a sample of this isotope gives a count rate of 450 counts per minute450\text{ counts per minute}450 counts per minute.
Without the source, the background count is 30 counts per minute30\text{ counts per minute}30 counts per minute.
What is the count rate due to the source after 12 hours12\text{ hours}12 hours?
105 counts per minute105\text{ counts per minute}105 counts per minute
112.5 counts per minute112.5\text{ counts per minute}112.5 counts per minute
135 counts per minute135\text{ counts per minute}135 counts per minute
210 counts per minute210\text{ counts per minute}210 counts per minute
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.