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Attenuation Coefficients

For X-rays the attenuation is proportional

• to the electro density of the material
• (approximately linear proportional)
• to length of the travelled distance
• (inverse exponentially proportional)

Attenuation per distance is expressed via attenuation coefficient $\mu$

• Electron density $\approx$ atomic number (in the periodic system of elements)
• $\mu$ is linear proportional to the atomic number

For water the attenuation coefficient is about $0.15cm^{-1}$.

Example:

• Lead $Pb$ → atomic number 82
• Water $H_2O$ → atomic number ca. 8+1+1
• Thus, lead has a 10 times higher attenuation than water.