Positrons are antiparticles of electrons - Edexcel - GCSE Physics - Question 5 - 2014 - Paper 1
Question 5
Positrons are antiparticles of electrons.
The photograph shows a PET scanner that uses positrons to locate the site of a brain tumour.
Positrons are emitted by the ... show full transcript
Worked Solution & Example Answer:Positrons are antiparticles of electrons - Edexcel - GCSE Physics - Question 5 - 2014 - Paper 1
Step 1
1. Advantage
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Answer
An advantage of using fluorine-18, which has a short half-life, is that it minimizes the patient's exposure to radioactivity. As the radioactive substance decays quickly, the amount of time the patient is exposed to harmful radiation is reduced.
Step 2
2. Disadvantage
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Answer
A disadvantage of using a substance with a short half-life is that it has to be produced close to the place of use. This can limit the availability and logistical planning necessary for accessing the radioactive isotope in time for the scan.
Step 3
ii) Explain how this enables the site of the tumour to be located.
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Answer
When a positron emitted by fluorine-18 encounters an electron in the body, they annihilate each other, producing two gamma rays that travel in opposite directions. This annihilation event occurs at the location of the positron-electron interaction, which is likely near the tumour. Gamma cameras, positioned around the patient, detect these gamma rays simultaneously. By analyzing the timing and direction from which the gamma rays are detected, it is possible to triangulate the exact position of the tumour within the body, thereby facilitating precise imaging of the affected area.
