Optical Restoration of Lead Fluoride Crystals

Due to its relatively high resistance to high radiation, lead fluoride (PbF2) crystals are becoming an increasingly popular material of choice for electromagnetic calorimetry, such as for experiments requiring the measurement of high‐energy photons in Hall A of Jefferson Lab. For our studies we irradiated the PbF2 crystals using an electron linear accelerator (LINAC) followed by exposing the crystals to blue light so as to restore the nominal optical properties. This technique of optical bleaching with blue light affords an efficient and low‐cost means for reversing the deleterious effects of optical transmission loss in radiation‐damaged lead fluoride crystals. Whereas earlier experiments irradiated the PbF2 samples with 1.1 and 1.3 MeV gammas from 60Co, we used pulsed beams of energetic electrons from the tunable 25‐MeV LINAC at Idaho Accelerator Center of Idaho State University in Pocatello, Idaho. A 20‐MeV beam of electrons was targeted onto four separate 19 cm length samples of lead fluoride over per...