# Topic Questions: 1 understand that a tracer is a substance containing radioactive nuclei that can be introduced into the body and is then absorbed by the tissue being studied — 9702 P4 PET scanning > 1 9702 P4 PET scanning topic questions (2 marks) on 1 understand that a tracer is a substance… — 1 papers, 2025. Open the exact question in the original… - Canonical HTML: https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/1-understand-that-a-tracer-is-a-substance-containing-radioactive-nuclei-that-can-be/ - Markdown mirror: https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/1-understand-that-a-tracer-is-a-substance-containing-radioactive-nuclei-that-can-be/index.md --- CIE IAL · Physics · 9702 P4 · PET scanning 1 9702 P4 PET scanning topic questions are tagged to this syllabus point across 1 papers (2025). Only the parts whose knowledge graph matches this syllabus statement are counted, and the table shows which parts of each question are involved. - 1 topic questions - 1 papers - 2 tagged marks - 6.3% of topic questions - 7.4% of topic marks - 2025 - Syllabus 2025–2027 - [All 9702 P4 PET scanning topic questions](https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/) - [All paper codes](https://www.examsci.com/topics/) Core finding **This PET scanning syllabus point appears in 1 9702 P4 papers across 2025, contributing 1 topic questions and 2 marks.** The most recent appearance is 9702/44 October/November 2025. That equals 6.3% of the 16 topic questions and 7.4% of the 27 marks tagged to PET scanning. Only parts tagged to this subtopic are counted, so a four-part question can contribute one item and one part's marks. The table lists every matching question, its tagged parts and marks, with a link back to the paper page. Sessions are newest first, so the statement can be traced back through the full paper history. ## Topic questions by session Newest sessions first. Parts and marks count only the parts tagged to this subtopic; “x of y parts” shows how much of the question is tagged elsewhere. Select the paper cell to open the matching question on the paper page, or use **Go to Practice Hub** to answer that exact question in the Interactive Practice Hub. | Paper | Question | Type | Parts | Marks | Difficulty | Practice | | --- | --- | --- | --- | --- | --- | --- | | [**9702/44** October/November 2025 · CIE IAL](https://www.examsci.com/past-papers/cie-ial/physics/9702-paper-4/2025-october-november-9702-44/#q-8) | **Q8** PET Scanning and Radioactive Decay of Oxygen-15 - CIE A Level Physics 2025 Nov Paper 44 Q8 | FRQ | 1 of 8 parts ((a)) | 2 of 15 on the paper | Easy | [Go to Practice Hub](https://www.examsci.com/practice?set_id=188bcbde-77c7-4443-9dec-bdf3fb0f0df1&question_id=1a1cf776-459e-4292-895f-dfe9d984a990&source_detail=9702%2F44+October%2FNovember+2025) | ## Related topic questions in PET scanning - [2 recall that a tracer that decays by $\beta^+$ decay is used in positron emission tomography (PET scanning)](https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/2-recall-that-a-tracer-that-decays-by-beta-decay-is-used-in-positron-emission/) — 2 question items · 1 papers — 3 marks · 2025 - [3 understand that annihilation occurs when a particle interacts with its antiparticle and that mass–energy and momentum are conserved in the process](https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/3-understand-that-annihilation-occurs-when-a-particle-interacts-with-its-antiparticle/) — 9 question items · 3 papers — 14 marks · 2025 - [4 explain that, in PET scanning, positrons emitted by the decay of the tracer annihilate when they interact with electrons in the tissue, producing a pair of gamma-ray photons travelling in opposite directions](https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/4-explain-that-in-pet-scanning-positrons-emitted-by-the-decay-of-the-tracer/) — 5 question items · 3 papers — 7 marks · 2025 - [5 calculate the energy of the gamma-ray photons emitted during the annihilation of an electron-positron pair](https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/5-calculate-the-energy-of-the-gamma-ray-photons-emitted-during-the-annihilation-of-an/) — 3 question items · 2 papers — 7 marks · 2025 - [6 understand that the gamma-ray photons from an annihilation event travel outside the body and can be detected, and an image of the tracer concentration in the tissue can be created by processing the arrival times of the gamma-ray photons](https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/6-understand-that-the-gamma-ray-photons-from-an-annihilation-event-travel-outside-the/) — 1 question items · 1 papers — 1 marks · 2025 ## Topic question rules and edge cases **How many topic questions cover this syllabus point?** 1 question stems cover this subtopic across 1 papers, but only 1 tagged parts and 2 marks belong to it. Other parts of the same questions are assessed under different statements and are excluded from this page. **Which papers include this subtopic?** The table lists every matching session from 2025. Each row links to the question anchor on the paper page, where the full paper context and practice entry point are available. **Why can one question appear under several subtopics?** The parts of one question can assess different syllabus statements. Each part is counted under its own subtopics, so the same question stem can appear on several subtopic pages while each page lists only the parts and marks tagged to that statement. **Can I practise these questions with AI marking?** Yes. Open a paper from the table and use the Interactive Practice Hub entry point. The page itself is static HTML so search engines and retrieval agents can read the full question list without executing JavaScript. --- Full page with native tables, bar charts and Practice Hub links: https://www.examsci.com/topics/cie-ial/physics/9702-paper-4/pet-scanning/1-understand-that-a-tracer-is-a-substance-containing-radioactive-nuclei-that-can-be/