CAIE IGCSE Physics Half-Life with Background Radiation

Practise extracting half-life from count-rate tables and decay curves by separating background from source count before applying repeated halving.

Exam points

subtract the background count from each detector reading before testing for a halving
find two times where the corrected source count halves and read their interval as the half-life
after repeated halving, add background back when the question asks for the detector reading

[Maximum number: 3]

Strontium-90 $\left({ }_{38}^{90} \mathrm{Sr}\right)$ is a radioactive isotope that contains 38 protons and 52 neutrons. Strontium-90 decays to form an isotope of yttrium (Y) by emitting beta ( $\beta$ ) particles.

Yttrium is also unstable. A scientist places a sample of yttrium near a radiation detector. Table 9.1 shows the count rate recorded by the detector as the sample decays.

Table 9.1

Fig. 9.1

Use Fig. 9.1 to determine the half-life of yttrium. Show your working.
half-life = h [3]

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5.2.4.2—Half-life from data or decay curves question 1