A LevelPhysicsOCRTopic Questions6. Particles & Medical Physics6.11 X-rays

X-rays (OCR A Level Physics)

Topic Questions

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1a3 marks
a)
Describe the basic structure of an X-ray tube and explain how X-ray photons are produced.
You may draw a labelled diagram.
[3]

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1b4 marks
b)
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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1a1 mark

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.

q25-paper-2-nov-2020-ocr-a-level-physics

a)
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]

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1b3 marks
b)
With the help of a calculation, explain the minimum photon energy shown on the graph for pair production.

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1a2 marks
a)
A high-energy X-ray photon interacts with an electron of an atom through the Compton effect.

Describe this effect.

[2]

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1b4 marks
b)
The diagram below shows a beam of X-rays incident normally on some soft tissue.

q21b-paper-2-nov-2021-ocr-a-level-physics

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]

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1c2 marks
c)
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.

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