Half Value Layer

Half Value Layer

The half-value layer expresses the thickness of absorbing material needed to reduce the incident radiation intensity by a factor of two. There are two main features of the half-value layer:

• The half-value layer decreases as the atomic number of the absorber increases. For example, 35 m of air is needed to reduce the intensity of a 100 keV gamma-ray beam by a factor of two, whereas just 0.12 mm of lead can do the same thing.
• The half-value layer for all materials increases with the energy of the gamma rays. For example, from 0.26 cm for iron at 100 keV to about 1.06 cm at 500 keV.

The half-value layer expresses the thickness of absorbing material needed to reduce the incident radiation intensity by a factor of two. With a half-value layer, it is easy to perform simple calculations.
Source: www.nde-ed.org

Table of Half Value Layers (in cm) for different materials at gamma-ray energies of 100, 200, and 500 keV.

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Pair Production

See above:

Gamma Ray Attenuation

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Mass Attenuation Coefficient