Development Of Current Pulse Type Digital Spectrometer

With the development and deepening of socio-economic,scientific and technological research and application,the scope and practice of nuclear technology applications are increasingly diverse,and the range of doses and types of radiation required for radiation detection are becoming increasingly complex.In the past,amplifiers and spectrometers designed for specific types of detectors may have the limitation of losing pulse data at high count rate in the application,and the inability to obtain the information of the original pulse signal.Only the energy information of the radionuclide can be obtained.However,in some research applications,the need to extract the information of the original signal cannot be realized.At this time,it is necessary to develop a reliable nuclear signal analysis that can analyze various types of information carried by the nuclear pulse signal under high counting rate.The instrument should use the designed current pulse type digital spectrometer to solve the limitations of the current spectrometer.The acquisition of the original current pulse signal by the high-speed ADC,and the digital signal analysis and processing to obtain various types of information represented by it.The current pulse type digital spectrometer has the characteristics of high pulse pass rate,high count pass rate,and simultaneous acquisition of a plurality of original pulse information.This paper designs and implements a current pulse type digital spectrometer.This project is derived from the national key research and development project “Highresolution aerial gamma spectroscopy and airborne imaging spectroscopy”(2017YFC0602100).The main research results at this stage are as follows:Designed and developed a current pulse type digital spectrometer hardware system with a sampling rate of 500 MSPS,including high-speed analog pre-processing circuit,high-speed digital circuit,high-speed parallel real-time digital processing logic and multi-rail low-noise and high-load capability power system;The digital multi-channel board of the produced spectrometer is only 5cm×8cm.It adopts six-layer board design,including three signal layers,two ground layers,one power layer,small footprint,good signal integrity and power supply stability.Strong,the circuit has good heat dissipation performance.The digital multi-channel sub-board of the spectrometer can be multi-channel extended by multiplexing,and the spectrum base of the spectrometer adopts FPGA to control the USB architecture,and the highspeed transmission unit can fully utilize the high-speed parallel characteristics of the digital processing unit;For the complex design features of high circuit running speed,high current demand and relatively long data transmission distance,after the printed circuit board design is completed,the board-level printed circuit board signal integrity simulation,printed circuit board power integrity simulation and PCB thermal design simulation and other measures have helped improve the preliminary design,which makes the hardware function further perfect and the operation is more stable.The maximum stable supply current of the digital logic power supply reaches 3.5A,and the input signal noise is tested and controlled to 2.07 mV.Aiming at the high pass rate and the high speed characteristics of the current pulse signal,a fast full dual channel digital logic with an equivalent running speed of 500 MHz is designed.The real-time high count rate particle event trigger and particle event are based on the deconvolution fast channel.Acquisition,and based on the digital constant ratio timing slow channel to ensure accurate extraction of energy information;For the requirement of information analysis after the original current pulse signal acquisition,a high-speed real-time pulse time information acquisition,current pulse signal rise time acquisition,and a digital logic function realization module for current pulse signal fall time acquisition are designed.Each particle pulse extracts time information,and at the same time,for the circuit coupling detector output signal,when the impedance mismatch is likely to cause the input signal to generate jitter,a special logic anti-jitter design is performed,particle pulse is used to extract time information,and the time extraction precision reaches 2 ns;In view of the large logic operation amount,high logic operation rate and relatively tight timing in the logic chip,some auxiliary logic processing measures and units are used to ensure the stable operation of the versatility spectrometer logic.In the case of multiple digital logical clock domains working together in digital logic,a variety of forms of cross-clock domain processing are performed to reduce the probability of logical stability in digital logic due to competitive risks;For the transmission of high-speed information,the need for real-time analysis after large-capacity pulse information extraction,the development of scalable baseboard for energy spectrum synthesis and high-speed data transmission.Finally,the current pulse type digital spectrometer with extended capability is completed.The digital spectrometer is based on a pure FPGA structure,in which the analog input bandwidth is 190 MHz,and the continuous signal generated by the input signal generator can reach the pulse of 29 MHz at 99.9% pass rate.Input frequency,using NaI detector can achieve 95% of the live time and 7.69% resolution at the input pulse frequency of 99 Kcps,using LaBr3 detector,the resolution of the test can reach 3.0%,the second coincidence peak and main peak The ratio of counts is reduced to 0.13%.When the five sources are tested simultaneously,all five radioactive sources can be accurately obtained by peak finding.The analysis of the ray energy and the output peak position indicate that the linearity of the spectrometer reaches 0.9997.The current pulse signals of NaI and LaBr3 can also obtain the information of the rising edge and falling edge time of the signal more accurately,and achieve the design purpose of the current pulse type digital spectrometer.The spectrometer can be used for the measurement of products in spallation neutron source experiments and other energy spectrum measurements under high-activity activity conditions,as well as for the study of the response of various scintillators to different energy and species.