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09 February 2012

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

Answer posted on 16 October 2006. The information and material posted on this website is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Website. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.