Production and use of X-rays
Cambridge A-Level Physics (9702) · Unit 24: Medical physics · 7 flashcards
Production and use of X-rays is topic 24.2 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 24 — Medical physics , alongside Production and use of ultrasound and PET scanning. In one line: Contrast in X-ray imaging is determined by the differential absorption of X-rays by different tissues or materials. Tissues with higher atomic numbers or densities absorb more X-rays, appearing brighter in the image.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 7 flashcards — 2 definitions, 4 key concepts and 1 calculation — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
What determines contrast in X-ray imaging
Contrast in X-ray imaging is determined by the differential absorption of X-rays by different tissues or materials. Tissues with higher atomic numbers or densities absorb more X-rays, appearing brighter in the image.
What the Cambridge 9702 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Explain how bombarding a metal target with electrons produces X-rays, and calculate, from the accelerating p.d., the shortest X-ray wavelength that results.
- Understand how X-rays are used to image structures inside the body, including what contrast means in an X-ray image.
- Recall I = I₀e^(−μx) and use it to describe how matter attenuates X-rays.
- Understand that computed tomography (CT) builds up a 3D image of a structure inside the body in two stages: many X-ray images of one section, taken from different angles, are combined into a 2D image of that section; this is repeated along an axis, and the 2D images of the many sections are combined.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Production and use of X-rays
- › Calculate intensity ratio I/Io = e^(-μx), then subtract from 1.0 to find the absorbed fraction.
How are X-rays produced?
X-rays are produced by the rapid deceleration of high-energy electrons when they bombard a metal target, typically tungsten. This deceleration causes the electrons to lose energy in the form of X-ray photons.
What is the relationship between accelerating potential difference (p.d.) and the minimum wavelength of produced X-rays?
The minimum wavelength (λ_min) is related to the accelerating p.d. (V) by the equation: λ_min = hc/eV, where h is Planck's constant, c is the speed of light, and e is the elementary charge. A higher p.d. results in a shorter minimum wavelength.
What determines contrast in X-ray imaging?
Contrast in X-ray imaging is determined by the differential absorption of X-rays by different tissues or materials. Tissues with higher atomic numbers or densities absorb more X-rays, appearing brighter in the image.
State the equation for the attenuation of X-rays in matter and define each term.
The equation is I = I₀e^(-μx), where: I is the intensity of the X-rays after passing through the material, I₀ is the initial intensity, μ is the linear attenuation coefficient, and x is the thickness of the material.
Explain the principle behind Computed Tomography (CT) scanning.
CT scanning involves taking multiple X-ray images of a section from different angles. These images are then processed to create a 2D image of that section. This process is repeated along an axis, and the resulting 2D images are combined to form a 3D image.
How does the linear attenuation coefficient (μ) affect the intensity of X-rays passing through a material?
A larger linear attenuation coefficient (μ) signifies that the material absorbs X-rays more readily. Therefore, a larger μ will result in a greater decrease in X-ray intensity (I) as the X-rays pass through the material.
Describe two ways to improve the contrast in X-ray imaging.
Contrast can be improved by using contrast agents, which are substances that absorb X-rays more strongly than the surrounding tissue. Contrast can also be improved by adjusting the energy (kV) of the X-ray beam; lower energy beams are absorbed more readily, enhancing differences.
Review the material
Read full revision notes on Production and use of X-rays — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 24 — Medical physics
Production and use of X-rays sits alongside these A-Level Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Production and use of X-rays deck
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