A student measures the radiation count rate near a radioactive source. The counter displays a reading of 135 counts per minute. When the source is removed, the counter reading decreases to 12 counts per minute.
What is the rate of emission from the radioactive source, in counts per minute, after correcting for background radiation?
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.