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Absorption of X-Rays

Physics: AQA A Level, topic 10.5.3

Absorption of X-Rays

Absorption of X-rays is analogous to that of gamma radiation. The absorption follows an exponential pattern.

Half thickness

Half thickness

  • A 'half thickness' can be quoted for the thickness of material required to reduce the intensity of an X-ray beam by a half.
Intensity of x-ray radiation

Intensity of x-ray radiation

  • So:
  • I=I0e−μxI = I_0 e^{-μx}
    • I and I0 are the final and original intensities.
    • μ is the linear (absorption) coefficient.
    • x is the thickness of the material being penetrated.
  • The density of the absorbing material is a major factor in the value of μ, so that regions of similar material of different density will absorb at different rates.
Mass attenuation coefficient

Mass attenuation coefficient

  • Mass attenuation coefficient =μρ= \frac{μ}{ρ}
  • ρ is the density of the material.
  • Examples are:
  • Lung tissue = 6 cm²/g
  • Breast tissue = 4 cm²/g
    • These values are true at a photon energy of 10 keV.

Test yourself on Absorption of X-Rays

  • Which of these affects the absorption coefficient, μ?

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