Igcse Model Questions Vol1 2025 Physics Question 30

A radioactive isotope A has an initial activity of \(5.0\times10^{3}\ \text{Bq}\) and a half‑life of \(8.0\ \text{days}\). It decays to a daughter isotope B, which has a half‑life of \(2.0\ \text{days}\) and emits a \(0.5\ \text{MeV}\) gamma photon for each decay.\n\n(a) After how many days will the activity of isotope B reach its maximum value? Give your answer to one decimal place.\n(b) At that time, a lead shield of thickness \(2.0\ \text{cm}\) is placed between the source and a detector. The linear attenuation coefficient for the gamma photons in lead is \(\mu = 0.5\ \text{cm}^{-1}\). What fraction of the original gamma intensity from B reaches the detector? Give your answer as a decimal to three significant figures.