Cherenkov Glass Detectors with Wavelength Shifting Fibers for Neutron Measurements

Abstract

Two groups of Cherenkov glass detectors, containing six samples in total, have been produced in our laboratory with different compositions and configurations. The first group included three samples that were made of SiO2, and the other group contained three samples that were made of PbO+SiO2. All the samples were tested by using a PuBe source. Wavelength shifting (WLS) fibers were implemented in four samples (two from each group) to improve the light output of the Cherenkov detectors. Even though Cherenkov detectors have low noise due to the low-energy threshold and short decay constant (on the order of picoseconds), their light yield is low. A few hundred Cherenkov photons can be generated per mega-electron-volt. Without the WLS materials, most Cherenkov photons are likely to be absorbed within the glass sample before they can reach the photon sensor. WLS fibers do not directly increase the number of Cherenkov photons, but they can reduce the energy of Cherenkov photons and direct them toward the photon sensor. This photon energy reduction helps increase the efficiency of light collection and improves matching between photon wavelength and photon detector quantum efficiency. The objective of this work is to test Cherenkov glass detectors for the detection of neutrons by placing a 1-mm layer of Gd2O3 in front of the detectors. The focus is to increase the output light by observing the effect of the WLS fibers on the detection process with the use of different composition samples. The light output of the Cherenkov detectors was expected to increase more in the lead group than in the silicon group. Most of the Cherenkov energies are likely to be deposited within the glass sample. The approach is to direct the WLS photons to the photon sensor by allowing the energy deposition that takes place in the WLS fibers. A detailed model by Geant4 confirmed that the measured observations were reasonable. Both experimental and simulated results show an increase in light output when WLS fibers are added to the detectors.