A-level PHYSICS Paper 3 Section B Medical physics

Materials For this paper you must have: • a pencil and a ruler • a scientific calculator • a Data and Formulae Booklet • a protractor. Instructions • Use black ink or black ball-point pen. • Fill in the boxes at the top of this page. • Answer all questions. • You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages. • If you need extra space for your answer(s), use the lined pages at the end of this book. Write the question number against your answer(s). • Do all rough work in this book. Cross through any work you do not want to be marked. • Show all your working. Information • The marks for questions are shown in brackets. • The maximum mark for this paper is 35. • You are expected to use a scientific calculator where appropriate. • A Data and Formulae Booklet is provided as a loose insert. Please write clearly in block capitals. Centre number Candidate number Surname Forename(s) Candidate signature I declare this is my own work. A-level PHYSICS Paper 3 Section B Medical physics Time allowed: The total time for both sections of this paper is 2 hours. You are advised to spend approximately 50 minutes on this section. 2 *02* IB/M/Jun21/7408/3BB Do not write outside the Section B box Answer all questions in this section. 0 1 A hospital uses the radioactive isotope technetium-99m as a tracer. Technetium-99m is produced using a Molybdenum-Technetium generator on site at the hospital. 0 1 . 1 Explain why the value of the half-life of technetium-99m: • makes it suitable for use as a tracer • means that it must be produced in a generator on site. [4 marks] 0 1 . 2 Technetium-99m emits only gamma rays. Explain why this makes technetium-99m suitable for use as a tracer. [4 marks] 3 *03* Turn over ► IB/M/Jun21/7408/3BB Do not write outside the 0 1 box . 3 A gamma camera can be used to form images when using a tracer. Figure 1 shows a photomultiplier tube from a gamma camera. Figure 1 At the crystal scintillator, each photon of gamma radiation leads to the emission of one visible light photon. Describe how the current produced by the photocathode is amplified in the photomultiplier tube. [3 marks] Question 1 continues on the next page 4 *04* IB/M/Jun21/7408/3BB Do not write outside the 0 1 box . 4 Iodine-131 is a medical tracer that can be detected using a gamma camera. Iodine-131 has a physical half-life of 8.0 days. A patient is injected with iodine-131 that has an initial activity of 3.2 GBq. For this patient, the biological half-life is 66 days. For safety reasons, the patient cannot be discharged from hospital until the activity due to the iodine in the patient’s body drops to 1.1 GBq. Determine whether the patient can be safely released from hospital after 10 days. [4 marks