(a)[1]
Define what half-life means.
(b)[3]
A sample has $N_0$ nuclei of carbon-11 and no additional nuclei when $t = 0$. On Fig. 9.1, sketch how the number of boron-11 nuclei in the sample changes with $t$.
(c(i))[2]
Explain, referring to the random nature of radioactive decay, why the activity of the carbon-11 sample in (b) gets smaller with time.
(c(ii))[3]
State, with reasons, whether a radiation detector placed close to the carbon-11 sample gives a measured count rate that is less than, equal to or greater than the sample’s activity.