A GM tube detector measures background radiation in a laboratory over several minutes. Explain why the background count rate readings vary randomly from minute to minute.
With no radioactive sample present, the detector records a background count rate of 30 counts/minute30\text{ counts/minute}30 counts/minute. A student then places a radioactive sample near the detector and measures a total count rate of 270 counts/minute270\text{ counts/minute}270 counts/minute. After 15 hours15\text{ hours}15 hours, the total count rate of the sample and background is measured to be 60 counts/minute60\text{ counts/minute}60 counts/minute.
Calculate the half-life of the radioactive sample, clearly showing each step of your calculation.
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.