Describe the basic structure of an X-ray tube and explain how X-ray photons are produced. You may draw a labelled diagram.
[3]
A beam of X-rays is directed at tissues in a patient. The X-ray photons interact with the atoms of the tissues. Simple scatter is one of the attenuation mechanisms. Name and describe two other attenuation mechanisms.
[4]
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A high-energy X-ray photon interacts with an electron of an atom through the Compton effect.
Describe this effect.
[2]
The diagram below shows a beam of X-rays incident normally on some soft tissue.
The attenuation (absorption) constant of the soft tissue is 0.85 cm–1. The intensity of the beam is 4.6 × 103 W m–2. There is a small cyst 2.1 cm from the surface of the soft tissue. The cross-sectional area of the cyst normal to the beam is 3.4 × 10–4 m2.
The beam is switched on for 30 s.
Calculate the X-ray energy incident on the cyst in a period of 30 s.
energy = ....................................................... J [4]
The attenuation coefficients of the cyst and the soft tissues in (b) were similar. This prevented imaging the cyst using a two-dimensional X-ray image.
Name a different X-ray technique that could be used to image the cyst. Explain the advantage of this technique.
[2]
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X-ray photons interact with atoms.
The attenuation coefficient against lg(photon energy) graphs for simple scattering (S), photoelectric effect (PE), Compton effect (C) and pair production (PP) are shown below.
For the X-ray tubes used in hospital, the X-ray photons have energy of about 105 eV.
State the attenuation mechanisms for these photons.
[1]
With the help of a calculation, explain the minimum photon energy shown on the graph for pair production.
[3]
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