The Development Of On-line Neutron Incidence Vertex Correction Detection System Based On GEM Detector

With the development of neutron source technology,the performance requirements of neutron detectors are higher in various research fields.The price of ³He gas used for neutron detection has increased year by year,the research of new neutron detection technology to replace ³He neutron detector has become a hot spot in the field of particle detection.Neutron Gas Electron Multiplier（GEM）detectors based on the Polyethylene conversion layer and boron-coated drift are considered to be one kind of detector replacement for ³He neutron detectors due to their good position resolution,high detection efficiency,good plasticity and good time response in the future.The thesis proposes the idea of using time information and FPGA technology to optimize the position resolution of neutron sensitive GEM detectors on-line and developes a DAQ system,trying to solve the dilemma that the position resolution of the GEM detector neutron are greater than 1 mm using traditional detection method and the large raw data flux for Large sensitive area detection system.Time extrapolation based on the time information can improve the position resolution of thermal neutrons to 0.37mm compared to the position resolution of 2.27 mm obtained by the traditional centroid method.The online compression technology based on FPGA has a compression ratio of up to 85.32 for x-ray data.This thesis completed a data acquisition system based on GEM detector and APV-25 chip with multi-channel waveform sampling function.The feasibility of online data compression technology is developed and verified by x-ray data.Using the simulation data,alpha particle source experiment and thermal neutron source experiment to test the detection system and verify the correctness of the time extrapolation method.The specific research content includes the following four aspects:First,Geant4 and Garfield++software are used to simulate the energy deposition behavior of fast neutrons in Micro Pattern Gas Detectors.According to the electronic parameters,using 25 ns sampling period to digital simulation data,the motion behavior of ionized electrons and the sensing process of the readout board signal are studied scientific.The simulation results show that the center of gravity of the sampling period moves toward the incident direction with the evolution of time,but until the signal disappeared,the sampling center of gravity is still a distance from the incident point.The distance should be extrapolated from the direction of the heart to determine the point of incidence,the time extrapolation method is proposed.The simulation results show that the center of gravity of the recoil proton track is positively correlated with the movement of the center of gravity of each cycle,and the coefficient is only related to the experimental conditions.Second:the software and hardware design,processing and testing of the data acquisition system for the APV-25 integrated preamplifier chip is completed.The system used the I2C protocol to configure the APV-25 chip,and use the Ethernet protocol to transmit the digitized data of the APV-25 chip,a data acquisition system can control 16 APV-25 chips,a total of 2048 channels.In addition to completing the configuration of the basic parameters,the system also implements the function of reading 30 consecutive samples.The test results showe that the data transmission rate of Ethernet can reach 120 MB/s,and the linear range of the system is close to 100 k electrons.Ethernet-based acquisition software is written using Sockets and C++language,which can be easily ported to any complete Linux system.Third:The readout plate design assembly and basic performance measurement of the two-dimensional sensitive GEM detector s completed.The position resolution of the ⁵⁵Fe x-ray source is 127 um and the energy resolution is 18.7%.The cluster screening technology based on FPGA technology is realized,and the discriminating algorithm is verified by using x-ray experimental data and FPGA development board,the first layer algorithm of online track correction is implemented.Finally,the position resolution ofαparticle is measured using three ²⁴¹Amαsources and three slits.The position resolution obtained by the conventional centroid method is 9.10 mm,and the position resolution obtained by the time extrapolation method is 0.45 mm.The correctness of the time extrapolation method is verified.The results show that all tracks ofαparticles under the same experimental conditions can be corrected with one parameter,which greatly simplifies the online track vertex correction algorithm and lays the foundation for online vertex correction and data compression.The thermal neutron position resolution is tested using ²⁵²Cf and boron-coated drift poles.The positional resolution obtained by time extrapolation is 0.37 mm,which was much better than the 2.27 mm of conventional center-of-gravity.It is also found that the detection system has a certain n/γdiscrimination capability.The detection system and method are not only suitable for GEM detector,but also for gas detector with drift region and time resolution,such as MicroMegas detector and grid ionization chamber.