(a(i))[1]
Describe what an alpha-particle is made up of.
(a(ii))[2]
Explain how an alpha-particle causes ionisation in air.
(a(iii))[1]
State how the ionising effect of alpha-particles differs from that of beta-particles and gamma rays.
(b(i))[3]
Determine the time needed for the number of radon-222 atoms in this sample to fall to $1.5 \times 10^{3}$.
(b(ii))[1]
Suggest one reason why, in practice, the time for the number of radon-222 atoms to fall to $1.5 \times 10^{3}$ may be slightly different from the value calculated in (b)(i).