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08 October 2008

Answer to Question #5839 Submitted to "Ask the Experts"

Category: Industrial Radiation — Industrial Applications

The following question was answered by an expert in the appropriate field:

We are trying to compare the radiation shielding effects of a product versus lead. The testing laboratory used the mass attenuation coefficient versus the linear attenuation coefficient to do this calculation. The research scientist claims this is an unfair calculation. Can you explain the difference?

The attenuation of x rays and gamma rays follows an exponential curve, and attenuation is dependent upon both the thickness and the density of the shielding material.

The linear attenuation coefficient (cm^-1) is multiplied by the thickness of the material (cm) to calculate the reduction in the gamma-ray intensity. The linear attenuation coefficient assumes that the shielding material has a "standard" density, for example, lead is assumed to have a standard density of 11.35 g cm^-3.

The mass attenuation coefficient does not assume the shield material's density. It is effectively the linear attenuation coefficient divided by the material's standard density and has units of cm² g^-1. To calculate the attenuation using the mass attenuation coefficient, you have to multiply it by the actual material's density and its thickness.

John P. Hageman, MS, CHP

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