HalfValue Layer Calculation
The thickness of any given material where 50% of the incident energy has been attenuated is know as the halfvalue layer (HVL). The HVL is inversely proportional to the attenuation coefficient (m) and the two values are related by the following equation. Since m is normally given in units of cm^{1}, the HVL is commonly expressed in units of cm.
This relationship comes from the intensity attenuation equation.
It can be seen that if an incident energy of 1 and a transmitted energy is 0.5 (1/2 the incident energy) is plugged into the equation, the thickness (x) multiplied by m must equal 0.693 (since the number 0.693 is the exponent value that give a value of 0.5). X in this case is the halfvalue layer.
Example Calculation
What is the HVL for a material with a attenuation coefficient of 0.4/cm?
