Investigating performance of a scintillation radiation detector design

Abstract

The Super BigBite Spectrometer project in Hall A of the Thomas Jefferson National Accelerator Facility (JLab) is finalizing the design of a required radiation detector called the Coordinate Detector (CDet) for use in electro-nuclear scattering experiments. The CDet will be composed of two planes of scintillating bars (extruded at Fermilab) containing wavelength shifting (WLS) fibers that absorb scintillation light and transport it to photomultiplier tubes (PMTs) for detection. This thesis reports on measurements made on sample scintillating bars to assist in final decisions related to the detector design. Bars with two surface finishes were tested: (1) a TiO2 coating applied during extrusion; and (2) a machined-at surface subsequently wrapped with 1/4 mm thick aluminized Mylar. Each bar contained two 1 mm WLS fibers. Measurements were made to compare scintillation light output of these two finishes. Longitudinal and transverse measurements were made to determine PMT photoelectron yield dependence. It was found that the TiO2 coating and 1/4 thick aluminized Mylar wrapping performed the same within experimental uncertainty. Longitudinal dependence was consistent with expectations from attenuation in the WLS fibers, while transverse dependence shows a maximum yield near the center of the bar and drop-off closer to the edges.