(a)[1]
Define activity of a radioactive sample in terms of its decay rate.
(b)[3]
Explain why the way the activity of a radioactive sample changes with time is exponential.
(c(i))[2]
A single radioactive isotope in a sample decays to produce a stable isotope. Its activity is $180\,\text{Bq}$ at $t = 0$. After $8.4\,\text{min}$, the activity has fallen to $120\,\text{Bq}$. Find the decay constant, in $\text{min}^{-1}$, for the isotope.
(c(ii))[1]
Use your answer in c(i) to find the half-life, in min, of the radioactive isotope.
(c(iii))[3]
On Fig. 9.1, sketch how the activity $A$ of the sample varies with $t$ for values of $t$ from $t = 0$ to $t = 24\,\text{min}$.
(iii)[3]
On Fig. 9.1, sketch how the activity $A$ of the sample varies with $t$ for values of $t$ from $t = 0$ to $t = 24\ \text{min}$.