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.
144 exam-style questions on CIE IGCSE Physics 5.2.4a Half-life. Each one has a worked solution and a mark scheme showing where the marks go.