(a)[1]
Define the term half-life.
(b)[3]
A sample has $N_0$ carbon-11 nuclei and no other nuclei at time $t = 0$. On Fig. 9.1, sketch how the number of boron-11 nuclei in the sample varies with $t$.
(c(i))[2]
Explain, with reference to the random nature of radioactive decay, why the activity of the carbon-11 sample in (b) falls as time passes.
(c(ii))[3]
State, with reasons, whether a radiation detector placed close to the sample of carbon-11 shows a measured count rate from the sample that is less than, the same as or greater than the activity of the sample.