O-LevelPhysicsNuclear Physics5054/22 · May/June 2024 · Q99 Marks
Alpha particles are sometimes emitted from the nuclei of radioactive elements. This emission is both random and spontaneous.
- (a)Describe what is meant by 'spontaneous' emission.[1]
- (b)Describe the composition of an alpha particle.[2]
- (c)(i)Alpha particles are detected using the tracks shown in a cloud chamber or by the sparks produced in a spark counter. Describe the structure of either a cloud chamber or a spark counter. Include a labelled drawing of the apparatus.[3]
- (c)(ii)Describe how the emission of alpha particles is shown as random in the apparatus you described in (c)(i).[1]
- (c)(iii)A radioactive source produces 120 tracks in one minute in a cloud chamber. 6.0 hours later, the same source produces 15 tracks in one minute. Without the source present, no tracks are produced. Calculate the half-life of the radioactive isotope in the source. half-life =[2]
Mark scheme
Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.
- 9(a) happens by itself / is not affected or caused by external conditions, e.g. temperature, pressure, another nuclear emission, etc. / not affected by the length of time the nucleus has already existed / happens for no reason
- 9(b) two protons or two neutrons
- 9(b) two protons and two neutrons or a helium nucleus
- 9(c)(i) outline of cloud chamber with: either light or transparent window for viewing or outline of spark counter with fine wire and plate or grille close to wire
- 9(c)(i) source of vapour, e.g. alcohol or voltage applied between wire and plate / grille
- 9(c)(i) method of cooling clear, e.g. expand piston or dry ice or high voltage used (> 200 V)
- 9(c)(ii) time between tracks formed varies or number of tracks in a certain time varies or tracks go in any direction or time between sparks varies or number of sparks in a certain time varies
- 9(c)(iii) any halving seen, e.g. 120 → 60 or 3 half lives
- 9(c)(iii) 2(.0) Hours
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