Study On High Speed Acquisition And Digital Filtering Of Nuclear Pulse Signals

As one of the most important methods in the nuclear analysis method,nuclear energy spectrum analysis in nuclear instrumentation can obtain important information such as the structure of the material,the type and content of the constituent elements directly or indirectly through the acquisition and analysis of the energy spectrum of the subject.And its advantages such as high sensitivity,good accuracy,low destruction make it has been widely used in industry,agriculture,medicine,aerospace,environmental,energy,national security and other fields.The acquisition of the spectrum information requires the use of the nuclear spectrometer system to analyze and extract the amplitude information of the nuclear pulse signal.The traditional realization of acquisition of the spectrum,mainly use the electronic device to realize the amplification and simulation filter forming of nuclear signals in the simulated nuclear spectrometer system.In recent years,with the rapid development of high-speed,high-resolution ADC devices,various digital devices(such as FPGA,DSP,CPLD,etc.),it lays a solid foundation for the birth of new generation of high-performance,digital spectrometer system.Based on the high-speed ADC sampling,the realization of the all-digital nuclear spectrometer system which is characterized by digital filter forming technology for nuclear pulse signal is realistic.Based on this,the paper mainly studies the following problems in the acquisition and processing of the nuclear pulse signals in the digital nuclear spectrometer system.(1)It develops a set of FPGA-based nuclear pulse signals high-speed acquisition system.Taking the AD9226 and EP2C8 as the core,a set of high-speed acquisition system of nuclear pulse signals is designed.By means of full sampling and triggering sampling,the NaI detector is used to measure the Cs-137 and Co-60 sources,the Si-PIN detector is used to measure the Fe source in the sampling rate at 5MHz,10 MHz,20MHz and 50 MHz under the high-speed acquisition.(2)It builds a set of nuclear pulse signal digital filter forming processing platform.Through the study and analysis of the digital convolution theory of the nuclear pulse signals,the function convolution method and the digital Sallen-Key method are used to realize the trapezoidal(triangle)forming and Gaussian forming of the nuclear pulse signal.On the platform,the simulation results of the simulated nuclear signal and the actual sampled nuclear signal are sampled at different filtering forming schemes and different filter forming parameters respectively.Through the study of forming results and pulse accumulation identification.A platform with several sets of digital filtering forming algorithm is constructed.(3)It develops the performance evaluation of digital pulse forming method for nuclear pulse signals.After the digital pulse forming process,the nuclear signals have been further dealt such as baseline recovery,stacking identification and energy spectrum construction.Under the sample rate at 20 MHz,The same series of digital nuclear pulse signals are obtained by NaI detector(measured Cs-137)and the Si-PIN detector(measured Fe)respectively.Under the same filter forming parameters,using trapezoidal forming,triangle forming and Gaussian forming methods to deal with the obtained digital nuclear pulse signals respectively.The energy resolution and maximum pulse count rate of the obtained ? spectrum are: trapezoidal forming(7.5%,126),triangle forming(7.7%,127)and Gaussian forming(7.2%,123).The energy resolution and the maximum pulse count rate in the X-ray fluorescence spectrum are: trapezoidal forming(185eV,369),triangle forming(189eV,393),Gaussian Forming(183eV,346).Under the same filter forming method,different filter forming parameters are adopted.The larger the filter forming parameters are set in the acquired energy spectrum,the higher the energy resolution and the lower counting rate are obtained.