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Linear attenuation
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When a collimated beam of monoenergetic gamma-ray photons passes through a material, the interaction processes remove gamma-rays by absorption or by scattering the gamma-rays away from the detector direction.

The linear attenuation coefficient :

  • describes the probability of absorption occurring per unit length within the absorber material;
  • it is also sometimes related to the density of the absorber material and called the mass attenuation coefficient.

Linear attenuation coefficients for certain gamma energies and absorber materials are found from linear attenuation graphs.

Have a go! This simulation demonstrates how the absorption of gamma-ray photons varies with the thickness of absorber material and the type of absorber material. To explore the relationship between these parameters go to the graph plotting exercise here.

The intensity ratio is the ratio of transmitted intensity to initial intensity (I /I0), and is expressed as a percentage.


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1999, 2000 The University of Liverpool, Department of Physics

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