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Edexcel IGCSE Physics 7.13 Half-life calculations

Practise half-life calculations from activity, mass and count-rate data, including decay graphs, curves of best fit and age estimates.

Syllabus
First assessment 2019
Course
Physics 4PH1

Exam points

  • find the number of half-lives from time divided by half-life, then halve activity, mass or count rate
  • plot decay data, draw a smooth curve of best fit and read activity, atoms remaining or sample age
  • use a graph to determine half-life by reading when the activity or number of nuclei has halved

7.13 Half-life calculations question 1

[Maximum number: 5]

This question is about radioactive isotopes used for medical imaging.

Question (a)

(a)

lodine-131 is represented by this symbol.

53131I{ }_{53}^{131} \mathrm{I}
[ 5 ]

Question (i)

(i)

The cross ( x ) on the graph shows the initial number of atoms in a sample of iodine-131.

Draw three more crosses ( × ) on the graph to show how the number of atoms of iodine-131 in the sample changes during three half-lives.
[iodine-131 half-life =8 days]

Figure for Question (i) — Edexcel IGCSE Physics
[ 3 ]

Question (ii)

(ii)

Use a curve of best fit on the graph to estimate the time taken for the number of atoms in the sample to decrease to 5000.
time taken = days

[ 2 ]
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