The count rate from a sealed source is measured each day for a week. The count rate falls. Why does the count rate fall?
The nuclei in the source move more slowly as each day passes
The detector becomes less sensitive as the week goes on
Fewer undecayed nuclei are left in the source as each day passes
The radiation emitted carries less energy as each day passes
40 exam-style questions on AQA GCSE Physics 4.2 Atoms and nuclear radiation, covering 4.2.1 Radioactive decay and nuclear radiation, 4.2.2 Nuclear equations, 4.2.3 Half-lives and the random nature of radioactive decay, and 4.2.4 Radioactive contamination. Each one has a worked solution and a mark scheme showing where the marks go.