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?
44 exam-style questions on CIE IGCSE Physics 5.2.1 Background radiation and measuring count rate. Each one has a worked solution and a mark scheme showing where the marks go.