Research And Design Of Readout Electronics System For Underwater In-situ γ Detector Array

The mobile platform is equipped with nuclear radiation detectors to conduct rapid in-situ inspections of radioactively polluted water areas.However,due to the dilution of water and the diffusion of ocean currents,the content of characteristic radionuclides will decrease rapidly after the accident.At this time,it will be interfered by the strong background of natural radionuclides.The accurate identification of artificial radionuclides still has the problem that the detection efficiency and energy resolution cannot be satisfied at the same time.Therefore,based on the needs of in-situ nuclear radiation mobile surveys in water areas,based on the coupling of Silicon Photomultipliers(SiPM)and multi-channel scintillator crystals,this paper focuses on the research of multi-channel readout electronics systems,and builds a set of Miniaturized,multi-channel detector array system.On the basis of investigating the research work of related readout electronics,two key issues of large-area SiPM high signalto-noise ratio readout and accurate waveform digital acquisition are extracted.The specific research contents include the following aspects:1)Combining the historical nuclear accident data represented by the Fukushima nuclear accident and the Chernobyl accident and the measured data of radionuclides around Binhai Nuclear Power Plant in recent years,the energy measurement range and energy resolution of in-situ detectors in water areas were systematically analyzed.The overall performance requirements of these aspects have laid the foundation for the design of subsequent in-situ detectors in water areas.2)For large-area SiPM arrays,carry out research and design of front-end high signal-tonoise ratio analog readout circuits.By modeling the SiPM equivalent circuit model and the transfer function of the readout circuit,a theoretical analysis method for the signal-to-noise ratio of the analog readout circuit is established,and a transimpedance preamplifier and a second-order S-K filter are designed to realize the SiPM array readout and high-frequency Noise suppression;by using commercial multi-channel energy spectrum acquisition,the filter cut-off bandwidth corresponding to the best energy resolution is optimized.Tests show that the baseline noise of the analog readout circuit is only 2.04 m Vpp,the effective dynamic range is 67.57 d B times,and the best signal-to-noise ratio for 30 ke V pulse amplitude and baseline noise reaches 47.84.And the leading edge of the output pulse is only 382.1ns,making the detection range of the highest dose rate of the detector exceed 150μSv/h.3)Carry out research and design of multi-channel back-end waveform digital acquisition and processing circuits.Through the quantitative theoretical analysis of the front-end output signal,the ADC resolution and sampling rate index requirements are determined;combined with the mobile platform navigation speed,algorithm resources and peripheral requirements,a set of waveform digital acquisition and processing circuit system is designed.Through engineering methods such as low-pass filtering,effective digital-to-analog isolation measures,and differential transmission,the overall analog circuit signal baseline is reduced to 3.3m Vpp.4)System testing and analysis.The front-end analog readout part is packaged with a metal casing,and the back-end waveform digital acquisition and processing circuit is used for system testing.The results show that the least significant bit of the back-end waveform digital acquisition module is as high as 11.44bit@2MHz in the duration frequency band of the frontend analog output signal;the energy spectrum acquisition experiment of four channels,the best energy resolution reaches 4.71%@662ke V,in Under this gain configuration,the highest effective detection energy is 3.47 Me V.The formed multi-channel readout electronics system ensures good noise and event rate performance.In the future,it can be flexibly combined with scintillation crystals in terms of types and quantities to improve energy resolution and detection efficiency at the same time.The results obtained provide support for the improvement of the technical system in the field of nuclear radiation detection in waters in my country.