(a(i))[2]
Define the term radioactive half-life.
(a(ii))[2]
Show that the half-life $t_{\frac{1}{2}}$ and the decay constant $\lambda$ are linked by $\lambda t_{\frac{1}{2}} = 0.693$.
(b)[4]
Radon-222 is judged to be an unacceptable health hazard when its activity exceeds $200\,\text{Bq}$ in $1.0\,\text{m}^3$ of air. Calculate the minimum mass of radon-222 in $1.0\,\text{m}^3$ of air for which the health hazard becomes unacceptable.