(a) Define the term half-life of a radioactive nuclide.
(b) A freshly prepared sample contains N0 undecayed nuclei at t=0. Explain, without using any numerical calculation, how the number of undecayed nuclei changes successively after one, two and three half-lives.
(c) Sketch qualitatively the variation of the number of undecayed nuclei N with time t for a radioactive sample and describe how the half-life of the nuclide can be obtained from the graph.