(a)[3]
What does radioactive decay mean?
(b(i))[3]
Use the gradient of the line in Fig. 12.1 to find the activity, in Bq, of the sample at $t = 4.0\ \text{hours}$. Show your working.
(b(ii))[2]
Use your result in (i) to show that the decay constant $\lambda$ of the isotope is approximately $4 \times 10^{-5}\ \text{s}^{-1}$.
(c)[3]
A sample of a different radioactive isotope has an initial activity of $4.6 \times 10^{3}\ \text{Bq}$. It has to be stored safely until its activity falls to $1.0 \times 10^{3}\ \text{Bq}$. The decay constant of the isotope is $5.5 \times 10^{-7}\ \text{s}^{-1}$. The decay products are not radioactive. Calculate the shortest time, in days, that the sample must be stored.