Design of Large Scale Detectors Based on Polystyrene Solid State Scintillators Made of Granulated Polystyrene with WLS Fibers Light Collection
Test results of parameters of $~50\times 50 ~cm^2$ area scintillation detectors, produced of the commercial polystyrene granules with a technic of melting in a polished molding box are presented in a paper. The scintillators maximum emission spectrum is 425 nm and in comparison with block polymerized scintillators they have the same light yield in small samples, but significantly smaller volume transparency. The efficient scintillation light collection is realized with the help of 1 mm WLS fibers glued in grooves on the surface of the scintillator. An avalanche multipixel photodiode (SiPM) with $~2.5\times 2.5 ~mm^2$ sensitive area is used as a photo receiver.
The counter light yield for MIP detection reaches 60 photoelectrons, light collection nonuniformity not exceed 30%. For example, calculated MIP detection efficiency is 99.9% at 15 pe discriminator threshold and in this case the peak-value ratio in an amplitude spectrum is equal to 1.2 and event rate is about 1000 1/s. The noise counts created by only SiPM do not observed at this threshold.
The small sizes of SiPM and preamplifier allow one to create detectors without geometrical inefficiency zones and to cover by them areas of any size. Such detectors may be used in cosmic ray researches, guard systems and other applications.