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