Answer to Question #10730 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
What is the minimal required lead thickness as suggested by the National Council on Radiation Protection and Measurements (NCRP)? I have read several books; many contradict. I want to be sure that the right information is being given to my students.
Without any additional information, I'll assume that you are referring to shielding design for medical x-ray imaging facilities.
In NCRP Report No. 147, all of the curves that represent recommended shielding thickness start at zero and go up to some maximum. The short answer is that the minimal thickness is zero. In reality, the minimal amount of lead that you could use would be the smallest thickness that is commercially available.
This, however, does not completely solve your question. The NCRP report above is the reference that many medical physicists use to calculate shielding requirements for x-ray installations. The calculations that are used in this report include a number of parameters that affect the final result and, therefore, the amount of recommended shielding in a given barrier. These factors include dose limit to adjacent area, distance from the x-ray tube to the barrier, workload (number of patients, number of images taken, and assumed technical factors for the x-ray unit), and occupancy of the adjacent area. The amount of shielding recommended for a given barrier can vary significantly based on the input values of these parameters, which means that a blanket recommendation cannot be made for shielding thickness, nor can a minimal thickness be stated without performing the calculation for each barrier for a given installation using known or expected input parameters.
In order for you to provide the best information to your students, I recommend that you work through the methodology in NCRP Report No. 147 or attend a short course on this guide or see if you can contact a local medical physicist to speak to your students.
Kennith (Duke) Lovins, CHP