A radiation detector is placed close to a radioactive source that emits only β\betaβ-particles. Lead sheets of increasing thickness are placed between the source and the detector. Eventually, a lead sheet of thickness 5.0 mm is used. The count rate recorded by the detector decreases but does not drop to zero.
Why does the detector reading not fall to zero?
Some of the β\betaβ-particles are deflected around the edges of the sheet.
The detector is placed too close to the source.
There is always some background radiation being detected.
The lead sheet can never be thick enough to absorb all the β\betaβ-particles.
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.