A series of cameras for tomography on the Alcator C-Mod Tokamak (https://dspace.mit.edu/bitstream/handle/1721.1/95108/91ja002_full.pdf?sequence=1) required calibrated relative sensitivies They were over 20 years old at the time, and the wear and tear to the system made the relative sensities questionable. One theory was that exposure to thousands of plasmas and deposition of Boron or other materials had changed the foild transmission. Using an Amptek XR-100 (http://amptek.com/products/xr-100cr-si-pin-x-ray-detector/) a series of data was taken with a known X-ray source. Differences in the transmission were caclulated, to see if the sensitivity change was due to a deposit on the foil. Results showed that it was not the foil, but degradation in the amplifier circuit.