How would you answer part b(ii) of this question in the June 2012 paper3 (b) A γ ray detector with a cross-sectional area of 1.5 × 10–3 m2 when facing the source is placed 0.18 m from the source. A corrected count rate of 0.62 counts s–1 is recorded. 3 (b) (i) Assume the source emits γ rays uniformly in all directions. Show that the ratio number of γ photons incident on detector number of γ photons produced by source is about 4 × 10–3.
3 (b) (ii) The γ ray detector detects 1 in 400 of the γ photons incident on the facing surface of thedetector.Calculate the activity of the source. State an appropriate unit.