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Solutions: Radioactivity Questions

Q11.

(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 (not weight or size)

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

(5 marks)

(Total 7 marks)