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
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- explain that X-rays are produced by electron bombardment of a metal target and calculate the minimum wavelength of X-rays produced from the accelerating p.d.
- understand the use of X-rays in imaging internal body structures, including an understanding of the term contrast in X-ray imaging
- recall and use I = I0e–μx for the attenuation of X-rays in matter
- understand that computed tomography (CT) scanning produces a 3D image of an internal structure by first combining multiple X-ray images taken in the same section from different angles to obtain a 2D image of the section, then repeating this process along an axis and combining 2D images of multiple sections
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
- › Specify that the speed in the formula Z = ρc refers to the speed of ultrasound in the specific medium.
- › Consider all interfaces in a sample; a transmission percentage must be applied at every boundary where acoustic impedance changes.
- › 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.
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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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