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A 128-channel positron detection system will be constructed at Experimental Muon Source (EMuS) of China Spallation Neutron Source (CSNS) to conduct muon spin rotation/relaxation/resonance ($\mu $ SR) measurements. Each detector channel consists of a scintillator, a light guide, and a photomultiplier tube (PMT). The long light guide is bent to an “L” shape to propagate optical photons from the scintillator to the PMT. A series of Geant4 simulations and experiments has been performed to optimize the light collection performance of the L-bent detector. Geometry deformation induced by the bending process has been well modeled. Simulation results agree with the experimental tests. Accordingly, a novel hybrid wrapping method (scintillator with polytetrafluoroethylene (PTFE) and light guide with aluminum tape) has been developed to improve the amplitude of detector signals greatly. Compared to wrapping the detector with merely PTFE tapes or aluminum tapes, this method leads to an enhancement in light collection efficiency of 73% or 14%, respectively. Two optimally manufactured prototype detectors using the novel wrapping method have been tested at the ISIS Muon Facility. The beam tests demonstrated that the L-bent detectors can precisely measure the behavior of muon spins inside samples. Therefore, the L-bent detector design is competent for $\mu $ SR applications at CSNS/EMuS. [ABSTRACT FROM AUTHOR]

A 256-channel time-of-flight electronics system has been developed for a facility called “Back-n white neutron source (WNS)” in China Spallation Neutron Source (CSNS). This paper presents the structure and performance of the electronics system and test results at CSNS-WNS. A piece of lithium glass scintillator, coupled with a 256-channel multi-anode photomultiplier tube, is placed at the center of the neutron beam line as the detector. A 256-channel readout electronics system, including one front-end board (FEB), four time-to-digital converter (TDC) cards and one clock distribution module (CDM), measures the arrival time of each signal from the detector. Signals are sent to FEB from the detector through 15-cm cables and discriminated on FEB. FEB drives differential signals over 2-m cables to the TDC cards. Each TDC card has 64 channels, using a field-programmable gate array (FPGA) to measure the arrival time of each signal. The CDM supplies clock signals to the TDC cards to make them work synchronously. The TDC cards and CDM are housed in one peripheral component interconnect (PCI) eXtensions for Instrumentation chassis. The TDC cards achieve a timing precision of 3.5 ns. The electronics system meets the requirement of the experiment and is currently being used in CSNS. [ABSTRACT FROM AUTHOR]