The count rate measured near a radioactive source drops from 1064 counts per minute to 168 counts per minute in 15 hours. The background count remains constant at 40 counts per minute.
What is the half-life of the source?
333 hours
555 hours
7.57.57.5 hours
151515 hours
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.