A student measures the activity of a radioactive source using a Geiger-Müller counter. The total recorded count rate is 460 counts/min460\text{ counts/min}460 counts/min. When the radioactive source is removed, the detector continues to register a reading of 25 counts/min25\text{ counts/min}25 counts/min. What is the count rate solely due to the source, and what is the scientific term for the radiation detected when the source is removed?
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.