Radon-222 has a half-life of 3.82 days and is a radioactive element. If radon-222 is present in atmospheric air, it can be a health hazard. Safety measures ought to be taken whenever the activity of radon-222 is above 200 Bq per cubic metre of air.
(a(i))[2]
Define the radioactive decay constant.
(a(ii))[1]
Show that the decay constant for radon-222 is $2.1 \times 10^{-6}\ \text{s}^{-1}$.
(b)[3]
A volume of $1.0\ \text{m}^3$ of atmospheric air holds $2.5 \times 10^{25}$ molecules. Calculate the ratio $$\frac{\text{number of air molecules in } 1.0\ \text{m}^3 \text{ of atmospheric air}}{\text{number of radon-222 atoms in } 1.0\ \text{m}^3 \text{ of atmospheric air}}$$ for the minimum activity of radon-222 at which safety measures should be taken.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Likelihood of decay per unit time” …