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Attenuation Calculation

The linear attenuation coefficient (m) describes the fraction of a beam of x-rays or gamma rays that is absorbed or scattered per unit thickness of the absorber.  m basically accounts for the number of atoms in a cubic cm volume of material and the probability of a photon being scattered or absorbed from the nucleolus or an electron of one of these atoms.  m is used in the following equation to calculate the intensity of a narrow beam of penetrating radiation after it has traveled a given distance in a material. 

Where: Ix = the intensity of photons transmitted across some distance x
  I0 = the initial intensity of photons
  m = the linear attenuation coefficient
  x = distance traveled

Using the transmitted intensity equation above, linear attenuation coefficients can be used to make a number of calculations.  These include:

  • the intensity of the energy transmitted through a material when the incident x-ray intensity, the material and the material thickness are known.
  • the intensity of the incident x-ray energy when the transmitted x-ray intensity, material, and material thickness are known.
  • the thickness of the material when the incident and transmitted intensity, and the material are known.
  • and the material can be determined be determined from the value of m when the incident and transmitted intensity, and the material thickness are known.