Response to what is the best way to protect film from airport x rays

Martin, I don’t believe that either of us is knowledgeable enough about the physics of x-rays to understand the context and meaning of individual statistics. Being able to do math is one thing, understanding the context of the data is another. However, I have done some research on the web and have contacted a person who is qualified in these matters.

I sent the following e-mail to Joe V. Pace III of the Oakridge National Laboratory, Nuclear Analysis and Shielding Section, Leader of the Shielding and Dosimetry Group. The Bio and Vita for Mr. Pace can be accessed at: http://nas.cped.ornl.gov/nas-staf.html

“Mr. Pace, There is a discussion going on at an internet chat site dealing with photography. One of the issues that has come up is shielding of conventional photographic film from x-rays (primarily at airport security). One person says that silver is better than lead (for a given thickness of the metal) in protecting film from x-rays. He claims that it is because silver has a higher x-ray absorption factor than lead. Are these statements accurate? Thank you for your time.”

Here is the response from Mr. Pace:

“Mike: I'm not aware of the mass absorption coefficient (MAC) for Ag [Silver] being higher than Pb [Lead], unless it's become part of the Darwin Evolutionary Theory syndrome, which so many believe in these days. If u have access to Rockwell's Reactor Shielding Design Manual, or another reference which shows MACs, u'll see that the MAC for Pb & Ag approach each other in the 1-3 MeV region, but never cross. Additionally, the mass density of Pb is greater than Ag. The absorption is proportional to the Z number, which is higher for Pb than it is for Ag. Sincerely. JOE”

In addition I have found the following information at http://www.nucleonics-online.com/622.html entitled “Calculation of Transmission and Shielding”

“For practical applications, two Total Interaction Coefficients were defined as combinations of Partial Coefficients: The Attenuation Coefficient and the Energy Absorption Coefficient. It is these two coefficients that are being used for the calculation of Transmission and Shielding of photons [x-rays].”

This means that both absorption and attenuation [reduction] coefficients need to be considered. The following charts show that with respect to the Total Interaction Coefficients (absorption and attenuation), Lead (Pb) outperforms Silver (Ag). http://www.photcoef.com/212182.html http://www.photcoef.com/212147.html Note that Pb outperforms Ag even when considering the individual factors (attenuation and absorption).

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