Study And Improvement Of Scintillator Detector For GPPD Of CSNS

General Purpose Powder Diffractometer(GPPD)is one of the three spectrometers of China Spallation Neutron Source(CSNS)in the first phase.The large-area position sensitive detector is a key component of GPPD.The performance and simulation research of the large area neutron position sensitive detector for GPPD was developed.A new upgrading scintillator detector with less dead area and SiPMs readout is also developed to fulfill the requirement of the upgrade of the GPPD in the near future.The scintillator neutron position sensitive detectors are consist of ~6LiF/ZnS scintillator,wavelength-shifting fiber and multi-anode photomultipliers(M-PMTs).The key parameters of the detector,such as detection efficiency,position resolution and maximum counting rate has been tested in the BL20 of CSNS.The results show that the detection efficiency for 1.4?and 2.8?neutrons is 38.5±1.7%and 56.1±1.1%respectively.In accordance with simulation results,the detection efficiency is about46.1±2.0%for 2.0?neutrons.The pixel size of the detector is 4.0mm×4.0mm.And the detector has a good 2D imaging capability.The maximum counting rate of the detector is about 78kHZ.The nonuniformity of the detect efficiency is about 19.6%,which could be reduced to 14.9%after optimizing the threshold of each readout channels.But there are still some disadvantages for this version?detector,such as the dead area in the edge is too large,and the gain difference of each channel of M-PMTs has a significant influence on the uniformity of detection efficiency.In order to solve these problems,the 90°bending technology of the fibers was developed.The bending radius of the fiber was reduced from 3cm to 2.5mm,which can reduce the dead area from 25%to less than 5%.In order to verify the feasibility of the SiPMs replacing the M-PMTs,the noise characteristics and gain uniformity of silicon photomultiplier(SiPM)were studied.The detection efficiency and the position resolution of this detector based on SiPMs readout was simulated by Geant4.A small-area scintillation neutron detector prototype(10cm×10cm)based on SiPMs readout was developed,and the performance of the detector was tested in the BL20 of CSNS.The results show that the amplitude of the neutron signal is larger than150mV and the pulse width is about 2us when the supported overvoltage is 29.5V.In contrast,the pulse width of noise signal is less than 800ns.When the threshold is greater than 75mV,the average counting rate of noise signal is less than 0.05HZ.The pixel size of the detector prototype based on SiPMs readout is 2mm×2mm.The detector prototype has the good 2D imaging capability.The peak position of time-of-flight spectrum of neutron obtained by the detector prototype is in good agreement with the results of the standard ~3He tube.The detection efficiency of the prototype for the 1.4?and 2.8?neutrons is about 35.1%and 54.3%respectively,which is close to the detection efficiency of GPPP scintillation detector.The research of this detector prototype with SiPMs readout shows that the new version scintillator detector could be a good candidate upgrading detectors for the GPPD.