I have two laboratories for the calibration of Radiation Detection, Indication and Computation (RADIAC) meters. I am trying to find out if there is a certification body that specializes in proficiency testing for radiation measurement.

I don't recall ever seeing it, I do however know that NIST has a Radiation department that does PT's. Probably not too cheap, but atleast a backup option.

It might be worthwhile sending an email to NAPT to see if they have any inputs.

Another possibility that pops to mind is to check with the American Society for Nondestructive Testing: www.asnt.org

Certification bodies typically do not provide PT though they may participate or be part of ILC. That function is accomplished by the Regional MRAs (e.g., APLAC), by the ABs, and by PT provider organizations like NAPT and MeasurePT.

NIST does have a raditation department, and you may be able to use them as a piviot lab for your own ILC, just remember to calculate the results compared to NIST using APLAC PT 001, available as no-cost download from www.aplac.org

Hope this helps.