O-LevelPhysicsNuclear Physics5054/21 · May/June 2023 · Q108 Marks

Carbon-14 is an isotope of carbon. It undergoes radioactive decay with a half-life of 6000 years. The age of a sample of wood is found using the carbon-14 that it contains.

(a)Describe what happens during radioactive decay.[2]
(b)The count rate of the carbon-14 in the sample of wood is initially 1600 counts/minute. On Fig. 10.1 draw a graph to show how the count rate will vary over the next 24000 years. The initial count rate is already marked with an x. [Figure 10.1][2]
(c)Name the apparatus used to measure the radiation from the sample of wood and describe how it is used to measure the count rate.[2]
(d)Describe how the count rate from a sample of wood is used to find its age.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[B1] emission from the nucleus
[B1] of an alpha particle or beta particle or gamma (radiation)
[C1] at least three points plotted at (6000, 800), (12000, 400), (18000, 200) and (24 000, 100)
[A1] all points correct and smooth curve drawn
[B1] GM (tube and) counter (and timer)
[B1] measure number of counts in a specified time (e.g. 1 min) or subtract background count or tube connected to ratemeter
[B1] measure count rate of similar (mass) sample of living / fresh wood
[B1] use the graph to find time or description of use of half-life to find age

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