State what is meant by radioactive decay.

1. (a)State what is meant by radioactive decay.[2]
2. (b)(i)An unstable nuclide P has decay constant λ_P and decays to form a nuclide D. This nuclide D is unstable and decays with decay constant λ_D to form a stable nuclide S. The decay chain is illustrated in Fig. 12.1. The symbols P, D and S are not the nuclide symbols. Initially, a radioactive sample contains only nuclide P. The variation with time t of the number of nuclei of each of the three nuclides in the sample is shown in Fig. 12.2. On Fig. 12.2, use the symbols P, D and S to identify the curve for each of the three nuclides.[2]
3. (b)(ii)The half-life of nuclide P is 60.0 minutes. Calculate the decay constant λ_P, in s⁻¹, of this nuclide.[2]
4. (c)In the decay chain shown in Fig. 12.1, λ_P is approximately equal to 5λ_D. The decay chain of a different nuclide E is illustrated in Fig. 12.3. The decay constant λ_F of nuclide F is very much larger than the decay constant λ_E of nuclide E. By reference to the half-life of nuclide F, explain why the number of nuclei of nuclide F in the sample is always small.[2]

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