Fabrication and testing of a 3D double-stack RPC with 30 gas gaps for detection of high energy gammas

Abstract

Multigap Resistive Plate Chambers (MRPCs) are cost-effective detectors with a high-performance. They are easy to build and offer the possibility to cover large areas. They provide excellent time resolution and potentially good spatial resolution. In this context, a 3D RPC with 15 double-stack layers (30 gas gaps) free of parallax error is fabricated. The designed RPC has a 2D pixelated readout and the induced charge on the ground electrodes, gives the position in the third dimension. The simulation results show that in the X–Y plane the Full Width Half Maximum (FWHM) resolution is around 70 μm for 511 keV gammas, while for the Z-axis, which is perpendicular to the detector plane, a spatial resolution of around 560 μm can be achieved. The fill factor of the proposed detector with a pitch of 6.25 mm for SNR of 17 is around 0.13%, and the maximum achievable fill factor for the same setup and SNR of 42.5 is around 23%. The measured spatial resolution of the detector for a collimated Cs-137 point source is in good agreement with the simulation results. For an isotropic 511 keV gamma source at 0.95 cm distance of RPC detector, the experimental detection efficiency of constructed RPC at 1900V applied voltage is around 2.1%, which with a relative error of 7% is in good agreement with the simulation result obtained by GEANT4 (2.25%). With the same detector, at larger distances of the gamma source from the detector (clinical PET camera) a detection efficiency of around 5.09% is achievable. For small animal PET (100 mm radius) with ¹⁸F point source, the spatial resolution (Γ) of a PET system composed by 3D MRPC detectors with 2.25∗2.25 mm² and 1∗1 mm² pixel sizes, fabricated by commercial PCB technology (pitch = 6.25 mm) and Microlithography technology (pitch = 1.25 mm), would be 1.64 mm and 0.91 mm, respectively.