Intercalibration of photomultiplier tube test benches through precision testing of their internal photodiode

The tile calorimeters of the ATLAS detector of the Large Hadron Collider at CERN will require over ten thousand photomultiplier tubes. These photomultiplier tubes will be subjected to rigorous testing in order to ensure that they fulfill their operational requirements before installation in the detector. Testing such a large volume of photo-multiplier tubes on schedule has necessitated the construction of a number of test benches. These tests are performed by comparing the performance of photomultiplier tubes to that of a large-area photodiode. Intercalibration of these test benches is required to ensure that the test results are consistent at all test sites. This will be accomplished through precise testing of the photodiodes used in each of the test benches. This necessitated the design and construction of a unit capable of performing the precision testing of these large-area photodiodes.