9702 · 24.2
Production and use of X-rays flashcards
Revision flashcards for Cambridge 9702 Production and use of X-rays (syllabus 24.2). Flip, recall, then mark a real past-paper question.
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What are X-rays?
X-rays are a type of high-energy, ionising electromagnetic radiation with wavelengths typically ranging from 10⁻⁸ m to 10⁻¹³ m.
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What are the two primary mechanisms by which X-rays are produced in an X-ray tube?
Bremsstrahlung (braking radiation), which produces a continuous spectrum, and Characteristic X-rays, which produce a line spectrum of discrete energies.
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What is thermionic emission and its role in X-ray production?
Thermionic emission is the release of electrons from a heated metal filament (cathode), providing the initial electron stream that is accelerated to produce X-rays.
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How does the accelerating voltage ($V_a$) in an X-ray tube relate to the maximum energy ($E_{max}$) of the emitted X-ray photons?
The maximum photon energy is directly proportional to the accelerating voltage: $E_{max} = eV_a$. This corresponds to the minimum wavelength, $\lambda_{min}$.
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Name two ways to increase the overall intensity of an X-ray beam.
1. Increase the accelerating voltage (produces more energetic, 'harder' X-rays). 2. Increase the filament current (produces more electrons and thus more photons per second).
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What is X-ray attenuation?
Attenuation is the reduction in X-ray beam intensity as it passes through matter, due to absorption (photoelectric effect) and scattering (Compton scattering).
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What is the formula for the attenuation of an X-ray beam?
$I = I_0 e^{-\mu x}$, where $I_0$ is initial intensity, $I$ is transmitted intensity, $x$ is thickness, and $\mu$ is the linear attenuation coefficient.
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What factors contribute to a sharp X-ray image?
A small focal spot, patient stillness, a close detector-to-patient distance, and a far source-to-patient distance.
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What is the purpose of an aluminium filter in an X-ray machine?
To filter out low-energy ('soft') X-rays, which would be absorbed by the patient's skin and increase radiation dose without contributing to the image.
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State one key advantage and one key disadvantage of CT scans compared to conventional X-ray imaging.
Advantage: Produces high-resolution, detailed cross-sectional or 3D images. Disadvantage: Involves a significantly higher dose of ionising radiation.
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How does a lead grid improve X-ray image quality?
It is placed between the patient and the detector to absorb scattered X-rays, preventing them from fogging the image and thus enhancing contrast.