International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators

4-8 May 2009, Vienna

Optical Restoration of Irradiated Lead Fluoride Crystals

A. Spilker¹, P.L. Cole¹, P. Bertin², T.A. Forest¹, M. Mestari¹, S. Naeem¹, J. Roche³, C. Muñoz Camacho², and N. LeBaron¹

¹Idaho State University, Dept. of Physics, Pocatello, Idaho, United States of America
²Université Blaise Pascal, Clermont-Ferrand, France
³Ohio University, Dept. of Physics, Ohio, United States of American

Corresponding Author: colephil@isu.edu

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 γs 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 periods of 1, 2, and 4 hours yielding doses between 7 kGy and 35 kGy. Samples were then bleached with blue light of wavelength 410 - 450 nm for periods between 19.5 and 24 hours. We performed this process twice – radiation, bleaching, radiation, and then followed by bleaching again – for each of these four PbF₂ samples. We shall discuss the efficacy of blue light curing on samples that have undergone two cycles of electron irradiation and optical bleaching.