Answer to Question #5099 Submitted to "Ask the Experts"

Q

In my building, there exists an old x-ray room. New shielding is required to bring this room up to code. I have been told by the state that certain walls need 1/32-inch lead shielding or the equivalent. Where can I find a list of materials and their lead equivalence? For instance, how much drywall would equal 1/32-inch of lead? Also, should I be concerned about the age of the lead-glass window? Does it lose shielding power over time? (It is probably 10 to 15 years old). Any help would be most appreciated. I am a physician and would like to operate the x ray machine in this space.

A

Answering the question from the inside out, information on shielding materials can be found in Report 147 of the National Council on Radiation Protection and Measurements, Structural Shielding Design for Medical X-Ray Imaging Facilities.

Regarding the shielding equivalence, the exact equivalence depends on the use of the room. I assume that this old room is a general-purpose room and that the walls under discussion are secondary barriers. From that report, the graph in Figure C2 indicates that the transmission of 1/32-inch of lead is about 0.008. To get that same transmission from wallboard, Figure C4 suggests, would take 220 mm, or eight inches and 11/16. Figure C3 gives the value for concrete as 125 mm, or approximately five inches. A contractor could tell you the cost of each. The lead is likely to be the easiest to do since a layer of 1/32-inch lead sandwiched between wallboard is available and simply mounted. No additional shielding cover is necessary for the nail or screws that hold the wallboard in place.

I have never heard of problems with old leaded glass. The lead does not defuse out of the glass over time. As long as it is not cracked, it should be fine.

Bruce Thomadsen, CHP