Development Of The 8.5atm 2D Multi-Wire Proportional Chamber For CSNS

China Spallation Neutron Source?CSNS?has been constructed in Dongguang,China.The flux of pulsed neutron beam can reach 2.5×10¹⁶(cm^-2s^-1).As a multi-purpose reflectometer device,the neutron detector should be designed to have a more than 50%?@2??detection efficiency,better than 2 mm position resolution and a200mm×200 mm effective area.The high pressure 2D multi-wire proportional cham-ber?MWPC?neutron detector filling³He gas is used as the key detector.A gas mixture of 6atm³He+2.5atmC₃H₈was used as the working gas of the high pressure MWPC neutron detector by simulation of the neutron conversion efficiency of³He gases at different pressures and the charged particles stopping ability of different hydrocarbon gases,fluorocarbon gases and inert gases.The performance of the high pressure MWPC neutron detector is decided by the design of the multi-wire chamber.The electric field,the gas gain and the induced charge distribution of the high pressure MWPC neutron detector were simulated with the different structures of the multi-wire chamber.The performance of the detector prototype was measured with the different structures of the multi-wire chamber,using the digital readout method and the center of gravity readout method.Based on the result of the simulation and experiment,the multi-wire chamber of the the high pressure MWPC neutron detector was completed design.The linearity performance of the MWPC detector across the anode wires is modulated by the discrete anode wires.The position linearity across the anode wires was measured and analysed,and a correction method of the anode wire modulation was obtained.The high pressure chamber was sealed by the aluminous ring and the sealing capability of the high pressure chamber was tested by the leak detection of helium mass spectrometer,vacuum and pressure maintaining.To solve the outgassing effect of the detector components and keep the stable operation,the recycled device was designed to have the purification function for the working gases.The high pressure MWPC neutron detector was tested with the Am/Be neutron source and the spallation neutron source after the detector was completed assembly.The detection efficiency of the high pressure MWPC neutron detector is about58%?70%with the design of 6atm³He.The position resolution of neutron is about1.4mm with the design of 2.5atm C₃H₈and the 100?m intrinsic position resolution of the detector.The maximum deviation between of the measuring position and the real position is reduced from 0.29mm to 0.12mm after the data is modified by the correction method of the anode wire mudulation.The high pressure MWPC neutron detector shows good n/?resolution and uniform irradiation responses in the active area of the detector with the measurement of Am/Be neutron source.The detector was tested in NO.20 beam line of CSNS,obtaining about 1.4mm 2D position resolution and good2D imaging ability.The high pressure MWPC neutron detector developed to meet the design requirements and has been installed.