The Research On The Readout Electronics For A Cosmic Ray Muon Tomography System Of High-Z Materials

Cosmic-ray Moun Tomography is a novel technology for high-Z material detection and monitoring. Traditional nuclear material detection technology based on the radioactive source, and it is difficult to detect shielded nuclear material. Penetrating cosmic-ray Mouns are a natural radiation background on the Earth, and they can easily penetrate a thick protective layer. When they traverse an object, such particles undergo Coulombian multiple scattering processes, which depend on the material atomic number Z and density. The measurement of the multiple scattering angles can be used to detect and image an object containing high-Z material without the use of artificial radiation and in a nondestructive way. And this technology can detect shielded high-Z material and discriminate it from low-Z background material.Cosmic-ray Moun Tomography technology has great advantages in the monitoring of the illegal transport of nuclear materials. A number of domestic and foreign research institutions have carried out numerous studies of this technology. The Northwest Institute of Nuclear Technology (NINT) plans to build a cosmic ray muon imaging system based on the drift chamber, and the entire system consists of the drift chamber detector and its preamplifier, readout electronics, data acquisition and image reconstruction. The position resolution of the imaging system is expected to reach50μm, and the pixel size is expected to reach millimeter or even sub-millimeter. The prototype of the imaging system includes eight drift chamber detectors adding up to208signal wires.According to the design objective of the imaging system, the electronics system must meet the following technical requirements:1、With the measurement range of0to500ns, the time measurement accuracy should be less than100ps.2、With the measurement range of15fC to1800fC, the quantity of electric charge measurement accuracy should be less than15fC.Therefore, the readout of multi-channel signal, high-precision time and charge measurement are the difficulties of the design.After analysing the signal characteristics of drift chamber detector and the requirement of readout electronics system, we decided to use following technology routes in the design of circuit board:the board is divided into two parts, time measurement and charge measurements; the time measurement part uses a TDC (Time-to-Digital Converter) chip to achieve high-precision time measurement, after determining the timing point of the input analog signal; the charge measurement part uses an ADC (Analog-to-Digital Converter) chip to do an accuracy sample, and uses the numerical integration method to calculate the quantity of the electronic charge; after processing in the FPGA (Field-Programmable Gate Array) and the CPLD (Complex Programmable Logic Device), the data is sent to the computer via the VME interface (the Versa Module Eurocard) for further analysis processing; the data processing and the control functions are done by the FPGA. The dissertation introduces the design of the readout electronics prototype in details, including the technology route and the implementation methods mentioned above. The Time Measurement Evaluation Board (TMEB), which is designed in the pre-research stage, is also introduced in the dissertation.Aiming at the imaging system of high-Z material with cosmic rays, which is based on the drift chamber detector, the dissertation designed its readout electronics prototype. The detection system using cosmic-ray moun is a hot topic recently, and the research on this type of detection system based on the drift chamber has not been reported in China. In the course of the design of readout electronics, the dissertation made the following innovative works:1、A TDC-GP2is used to achieve low-cost high-precision time measurement, and the accuracy of the electronics system is better than100ps.2、A FPGA with embedded DSP core is used to achieve real-time charge calculation through the numerical integration method, and a soft-core is used to achieve high-speed data reception.3、The TMEB is designed and tested, and it provides a basis for the technical scheme selection of the readout electronics prototype.Up to now, the design of the TMEB has been completed, and a series of electronics tests have been done. The test results demonstrate that the time measurement chip and the timing method fulfill the design requirements. The design and manufacture of the readout electronics prototype has finished, and the electronics tests are already underway. Future work will include a further test combined with the drift chamber detector.