2022 · Specimen · 9702/04 | Q11

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Question (11 of 12)8 marks · Practise this topic →

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Available practice: 77 of 100 marks. Parts 1(b), 4(b)(i), 4(c), 6(a)(ii), 6(b)(ii), 7(a)(i), 7(a)(ii), 9(b)(i), 9(c), 10(b)(ii) await marking support. Scores cover available parts only.

Positron emission tomography (PET scanning) makes use of a tracer containing a radioactive material that decays by positron emission.

(a)(i)State what is meant by a tracer.

Answer guidance

State A short answer. No explanation is needed, and adding one cannot earn extra marks.

[2 marks]

(a)(ii)State the name of the particles that are emitted from the body and detected by the detectors during PET scanning.

Answer guidance

State A short answer. No explanation is needed, and adding one cannot earn extra marks.

[1 mark]

In PET scanning a tracer containing a radioactive material that decays by positron emission is used, and particles (gamma-ray photons) are emitted from the body and detected by the detectors.

(b)Explain how these particles are created from positrons.

Answer guidance

Explain Give reasons, not just what happens. Each distinct reason is usually worth a mark.

[3 marks]

In PET scanning, gamma-ray photons emitted from the body are detected. Positrons can be artificially created by a process in the laboratory that is the reverse of annihilation. This process creates both a positron and an electron moving at the same speed in opposite directions.

(c)Suggest why two of these photons are needed to create one positron.

Answer guidance

Suggest More than one answer may be acceptable, so long as it is consistent with the physics.

[2 marks]

9702/04/SP/22Cambridge International AS & A Level Physics 9702 · Specimen 2022 · Paper 4 · Question 11