Research On Readout Method Of Boron-coated MWPC For Thermal Neutron Detection

Research on neutron, especially on neutron scattering, is a hotspot in contemporary science and technology. Neutron can penetrate deeply into a sample without being scattered or absorbed, which makes it an important experimental technique used in crystallography, physics, physical chemistry, biophysics, and materials research. Mostly, neutron scattering experiments are equipped with position sensitive detectors.3He is one of the best choices in gas proportional detectors for thermal neutron’s detection, for its huge neutron capture cross section. However, the limited production restricts further development of 3He as material of neutron detectors. Therefore,10B coated detectors, as a powerful alternative for this purpose, have attracted much more attention nowadays. This thesis targets a specific boron coated M WPC with an effective area of 20cm*20cm. To get a proper position resolution, delay-line readout method matched with TDC based on FPGA is adopted.The research contents of the dissertation consists of 4 parts:1. Research on readout methods. Establishing a readout model for analyzing how to read MWPC signal out with delay lines. This method can be a guidance for the design of frontend electronics.2. Implementing a FPGA based TDC with high resolution and density.3. Flexible system architecture for MWPC readout, with high performance and expansion capability.4. Pointing out basic ideas of judgement, rejection and recovery of pile-up events.The dissertation is organized as follows:Chapter 1 starts with the introduction of neutron’s basic property and several light nucleus reactions with thermal neutrons, which induces the feasibility and necessity of 10B coated gas detectors. Common position sensitive detectors for thermal neutron detection are listed, among which MWPC is emphatically introduced, including corresponding electronic readout methods.Chapter 2 concerns with running detector and electronic systems of some neutron scattering spectrometers. Most detectors are still based on 3He other than 10B, while the similarity of basic thoughts provides references to current study.In Chapter 3, parameters of 10B coated MWPC for this dissertation are described in detail, and a function model of the. original signal is established. Based on this, the network model of delay-line method for MWPC is analyzed, which finally guides the parameter selection and specific design of delay-line module.Chapter 4 and Chapter 5 respectively introduces frontend and backend electronics. Frontend electronics includes amplifier and discriminator, and backend electronics is mainly composed by high-resolution TDC based on FPGA and gigabit Ethernet interface based on FPGA SOC. The overall system architecture is summarized in the end of Chpater 5.Chapter 6 is the discussion of pile-up events handling in MWPC detection. Except for processing method in FPGA matched with this frontend electronics, further possible ideas are summarized and introduced for applications with larger scale or higher events rate.In Chapter 7, independent test of each electronic module and system test including all components are discussed. Test purpose, procedures and results are all listed, to testify the validity of designing readout method.In the final one, Chapter 8, conclusions of this dissertation is drawn and outlooks for next research is introduced. Further improvement of structure and performance can be benefit for adopting achievements of this dissertation to applications of the thermal neutron scattering.