5. (a) Positrons are antiparticles of electrons - Edexcel - GCSE Physics - Question 5 - 2014 - Paper 1
Question 5
5. (a) 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 ... show full transcript
Worked Solution & Example Answer:5. (a) Positrons are antiparticles of electrons - Edexcel - GCSE Physics - Question 5 - 2014 - Paper 1
Step 1
1. Advantage
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Answer
Using fluorine-18, which has a short half-life, minimizes the patient’s exposure to radioactivity. This means that the radioactive substance will decay quickly after the scan, reducing any potential long-term radiation effects.
Step 2
2. Disadvantage
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The main disadvantage is that the substance must be used close to the place and time of use due to its rapid decay. This can create logistical challenges in terms of availability and timing, particularly in emergency medical situations.
Step 3
ii) Explain how this enables the site of the tumour to be located.
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When a positron emitted from the fluorine-18 encounters an electron in the body, they annihilate each other, leading to the production of gamma rays. These gamma rays are emitted in opposite directions, creating a pair of photons that travel at 180° to one another. By placing detectors or sensors around the patient, the PET scanner can simultaneously detect these gamma rays. Because the momentum of the gamma rays is conserved, their detection allows for triangulation, enabling the precise location of the glucose that has accumulated at the tumour site to be identified.
