In order to predict and improve the performance of pixelated detectors, it is important to understand the optical
properties of the basic unit of the scintillating structure in the detector. To measure one of the essential optical properties,
reflectance, we have used a device composed of a laser and photodiode array. We have also developed an analytical
model of the optical phenomena based on Snell's law and the Fresnel equations to simply analyze measured results and
reflectance parameters at the interface. The computed and experimentally measured results typically have good
agreement, validating the analytical model and measurements. The optical parameters are used as inputs to GEANT4 .
The simulations are then leveraged to optimize an imager design before a prototype is built.
The optical reflectance was measured by using relatively inexpensive samples. A sample has scintillator, glue, and
septum (reflector) layers, and each sample has a different scintillator surface (polished/rough) and/or reflector [ESR
film/aluminum-sputtered (coated) ESR film] condition. A high-refractive-index hemisphere was attached on the top
surface of a sample to increase the maximum incidence angle at the scintillator-glue interface from 27° to 52°. The
sample including ESR film demonstrated average reflectance approximately 1.3 times higher than that from the sample
with aluminum-sputtered ESR film as a reflector, and the polished surface condition showed higher reflectance than the
rough-cut surface condition.