A student uses a Geiger-Müller tube and a counter to measure the background radiation in a laboratory.
The reading on the counter is 28 counts per minute.
The student then places a gamma radiation source 20 cm in front of the Geiger-Müller tube.
The new reading on the counter is 385 counts per minute.
Calculate the count rate that is detected from the gamma source alone.
90 exam-style questions on Edexcel GCSE Physics 6.3 Nuclear equations and decay. Each one has a worked solution and a mark scheme showing where the marks go.