Research On Digital Energy Spectroscopy Measurement System

As the great advantages of digital energy spectroscopy system on the measurementof energy spectrum, signal processing algorithm and system implementation have beendeeply studied over the past three decades abroad. Now, digital nuclear detection systemhas been used in all aspects of nuclear detection. However, domestic digitizedspectroscopy system is studied in terms of processing algorithm and systemimplementation in recent decade, and the technology is not very mature. According tothe paper arrangement, Gaussian shaping algorithm and trapezoidal shaping algorithmare simulated and compared by creating a simple simulation model from the nuclearsignal characteristics. The real-time processing system is implied by using FPGA. ARMcontrols FPGA configuration and parameter settings. Data is transferred to computer byUSB cable. Finally, spectroscopy curve is displayed on the computer and the system istested.Algorithm simulation chapter analysis the Gaussian shaping and the trapezoidalshaping theory and create a model to simulate and compare. The influence of Ray countrates to the preamplifier output signal amplitude and ballistic loss caused bypreamplifier decay time constant or the sampling rate are analyzed. Then the realizationof the two kinds of shaping algorithm and shaping shapes are analyzed. The output peakvariation of shaping algorithm in different preamplifier decay time constant orionization depth, sampling rate, shaping time are analyzed. FPGA real-time processingsystem is implied by using EP2C8Q208C8N chip of Altera. It includes a control module,Clock module, slowly shaping module, pulse pile-up and discrimination module,spectroscopy storage and output module. Trapezoidal shaping algorithm is realized bypipeline. Algorithm order is reasonably adjusted. The accuracy of shaping output isachieved by using fixed-point decimal multiplication operation. The pulse signal isdiscriminated by smoothing filter, hysteretic comparator, forward and afterward pile.Data stores and outputs by using dual-port RAM. All of module function and timingwaveform are verified by function simulation and gate-level simulation. ARM controlsFPGA configuration and parameter setting by a character device driver andcommunicates with computer by USB human interface device. PC window programachieves spectrum curve and the device’s control parameters setting by using dialog.The window regularly updates spectrum curve by timer and avoids graphics flicker by using memory buffer. Then the functions of device program and PC program areverified properly by debugging. Finally the PCB is designed by using PADS9.5and itssignal integrity and power integrity are simulated. At last the system is tested, includeboard noise, FPGA real-time processing system, the square wave spectrum curve indifferent shaping time, linearity of spectrum and Am241α-ray spectroscopy. The resultsshow system all modules’ functions are correct and system has good linearity ofspectrum, it is able to complete the spectrum measurement and display functions.