An instrument on a space probe uses a point source of gamma radiation to calibrate its sensors. A detector with a flat window of area 0.18 m2 is mounted at a distance of 2.4 m from the source, such that the face of the window is normal to the line joining it to the source. The source emits gamma photons isotropically (uniformly in all directions) at a constant rate of 8.0 × 104 s-1. Assuming no attenuation of gamma rays by any intervening medium, how many gamma photons enter the detector window per second?
200 s−1200\text{ s}^{-1}200 s−1
400 s−1400\text{ s}^{-1}400 s−1
800 s−1800\text{ s}^{-1}800 s−1
2500 s−12500\text{ s}^{-1}2500 s−1
128 exam-style questions on AQA A Level Physics Radioactivity (A-level only), covering Rutherford scattering (A-level only), $\alpha$ , $\beta$ and $\gamma$ radiation (A-level only), Radioactive decay (A-level only), Nuclear instability (A-level only), Nuclear radius (A-level only), Mass and energy (A-level only), Induced fission (A-level only), and Safety aspects (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.