A Geiger-Müller detector is used to measure the radioactivity of a sample. With the sample present, the detector registers a count rate of 450 counts per minute450\text{ counts per minute}450 counts per minute. When the sample is removed, the detector registers a background radiation count rate of 30 counts per minute30\text{ counts per minute}30 counts per minute.
What is the corrected count rate of the sample?
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.