Solutions: Radioactivity Questions
(a) Suggest two reasons why an particle causes more ionization than a particle of the same initial kinetic energy.
An alpha particle has much more mass/momentum than beta particle
An alpha particle has twice as much charge as a beta particle
An alpha particle travels much slower than a beta particle
(2 marks MAX)
(b) A radioactive source has an activity of 3.2 × 109 Bq and emits particles, each with kinetic energy of 5.2 MeV. The source is enclosed in a small aluminium container of mass 2.0 × 10–4 kg which absorbs the radiation completely.
(i) Calculate the energy, in J, absorbed from the source each second by the aluminium container.
In one second 3.2 × 109 alpha particles are emitted.
Total energy emitted = 3.2 × 109 x 5.2 x 106 x 1.6 x 10-19 J
= 2.66 x 10-3
= 2.7 x 10-3 J = 2.7 mJ
This energy is absorbed by the container so
energy absorbed = 2.7 mJ
(ii) Estimate the temperature rise of the aluminium container in 1 minute, assuming no energy is lost from the aluminium.
specific heat capacity of aluminium = 900 J kg–1 K–1
Heat gained by container = mc
In one minute - heat gained = 60 x 2.7 x 10-3 J = 0.162 J
= 0.162/(2.0 × 10–4 x 900)
Temperature rise = 0.90 K
(Total 7 marks)