A mineral specimen is analysed and found to contain the stable isotope lead-206. When the mineral crystallised, it contained uranium-238 but did not contain any lead-206.
Uranium-238 decays via a series of short-lived intermediate steps into stable lead-206. The half-life of uranium-238 is 4.54.54.5 billion years. The half-lives of any intermediate nuclides are negligible.
The specimen currently contains 333 atoms of lead-206 for every 555 atoms of uranium-238.
How long ago did the mineral crystallise?
1.91.91.9 billion years
3.13.13.1 billion years
4.14.14.1 billion years
7.27.27.2 billion years
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.