Photon flux monitor for a mono-energetic gamma ray source

A novel photon flux monitor has been designed and tested for use at the Duke University High Intensity Gamma Source. The five-scintillator-paddle system detects recoil electrons and positrons from photoelectric, Compton and pair-production processes. It is designed to be insensitive to gain and detector threshold changes and is usable for photon energies above 5 MeV. It has been calibrated using direct counting with a NaI detector, and its efficiency has been shown to be well described by a GEANT4 simulation.