A scientist is measuring the activity of a radioactive sample. The radiation detector records a total count of 450 counts over a period of 5 minutes. The average background radiation count rate in the laboratory is 15 counts per minute (cpm)15\text{ counts per minute (cpm)}15 counts per minute (cpm).
What is the corrected count rate of the radioactive sample in cpm\text{cpm}cpm?
75 cpm75\text{ cpm}75 cpm
90 cpm90\text{ cpm}90 cpm
435 cpm435\text{ cpm}435 cpm
105 cpm105\text{ cpm}105 cpm
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.