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Example Attenuation Coefficients
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Water has the attenuation coefficient $\approx 0.15cm^{-1}$.
Meaning that $D_{\frac12_{H_2O}}=\frac{ln 2}{0.15cm^{-1}} \approx 46mm$.
Strictly speaking, the attenuation coefficient is not constant but rather dependent on the energy of the gamma radiation. In the following the attenuation coefficient (in $cm^{-1}$) given for a selection of materials and gamma-energies ranging from 100 over 200 to 500 keV:
| Absorber | 100 keV | 200 keV | 500 keV |
|---|---|---|---|
| Air | 0,000195 | 0,000159 | 0,000112 |
| Water | 0,167 | 0,136 | 0,097 |
| Carbon | 0,335 | 0,274 | 0,196 |
| Aluminum | 0,435 | 0,324 | 0,227 |
| Iron | 2,72 | 1,09 | 0,655 |
| Copper | 3,8 | 1,309 | 0,73 |
| Lead | 59,7 | 10,15 | 1,64 |
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