Dual response of RE-doped sol-gel silica fibers to high energy electrons

Rare-earth doped sol-gel glasses were proven to be suitable materials for scintillating optical fiber sensors, to be employed in real-time medical dosimetry. To exploit the high granularity and flexibility of calorimeters made of fibers, their use as the active scintillating material in a sampling electromagnetic Spaghetti Calorimeter (SpaCal) or as the scintillating component in a dual-readout calorimeter, coupled with undoped fibers acting as Cherenkov radiators, has also been recently proposed. Besides crystalline fibers, active research on silica fibers is also being carried on. An extremely good radiation hardness is a crucial property for high-energy physics applications: previous results of irradiation tests on Ce-doped silica fibers with X- and gamma -rays up to 10 kGy pointed out the formation of radiation-induced defects, however an improvement of radiation resistance by reducing Ce content inside the fiber core was achieved, paving the way for further material development. Here we present an in depth characterization of Ce-doped sol-gel silica fibers under GeV electron beam exposure: silica fibers were tested in a SpaCal prototype and the analysis of their response suggests the possibility of a dual readout of Cherenkov and scintillation light simultaneously with the same doped silica fiber. An event by event pulse shape-based discrimination of Cherenkov and scintillation signals permits a separate study of linearity as a function of energy and attenuation length, taking advantage of the double side readout technique. The investigation of various mechanisms of interaction between radiation and sol-gel silica fibers as well as of their scintillation properties represents the goal of this work. An accurate comparison with their photoluminescence and radioluminescence response has been carried out, in order to optimize silica fibers performances as both scintillators and Cherenkov radiators.