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The Design and Preliminary Realize of Multichannel Gamma Spectrometer Based on LaBr3(Ce) Detectors

Author: ShangGuoXu
Tutor: TangBin
School:
Course: Circuits and Systems
Keywords: LaBr3(Ce) spectrum of gamma energy analysis of the multi-channel pulse
CLC: TL817
Type: Master's thesis
Year: 2013
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Abstract


Facing the shortage of uranium resources and the rapid development of nuclear powerindustry around the world, finding and exploitation and strategic reserve of nuclear fuelresources became the new focus of competition of countries around the world. Gamma-rayspectrometer can get gamma logging curve by detecting the field site gamma-ray, it alsoknown as gamma energy spectrum diagram. We can make quantitative explanation of thecontent of uranium, thorium and potassium in the seam through analysis of the gamma-raylogging curves, and get the parameters of rock and the information of related species. Basisof these information parameters and characteristics of different geological bodies, you candirectly find uranium or other mineral resources. Therefore, the continuously explore ofnew multichannel gamma-ray spectrometer has far-reaching significance.Currently, multiple gamma-ray spectrometers that used for identification, sniffing foruranium ore deposit and other mineral resources major use of CdZnTe detectors and NaIdetectors. CdZnTe detector is a new type of semiconductor detectors, its energy resolutionof low energy is better, but its efficiency is lower and the fast recognition of site can not beachieved; NaI detectors are scintillator detectors, which have a wide range of energy, butthe energy resolution is relatively poorer and difficult to met the requirements of analysisof uranium abundance and isotope identification. Targeted at the situation of energyresolution of multi-channel gamma-ray spectrometer is relatively poor, the design selectthe high resolution gamma ray detector, while further optimizing the structure of signalprocessing circuit and device parameter to reduction electronics noise and to improveenergy resolution of multiple gamma-ray spectrometer.This paper from miniaturization, low power consumption, good signal Gaussianshaping effect, reduce the baseline drift, accurately determine the peak arrival time andafter shaping the peak signal A/D sampling and other aspects of the Gamma-ray spectrometer to research it. Write your own PC testing software supporting the use of themulti-channel information acquisition board of gamma ray spectrometry. From thesimulation experiment to the test of the real radioactive sources, the major improvementsand designs of gamma spectrometer are as follows:(1)Use the LaBr3detectors instead of the conventional NaI detectors, to improve theintrinsic energy resolution of the gamma-ray detector.(2)Design amplifier circuit with programmable amplifier chip, design amplificationcircuit use programmable amplifier chip THS7002I, this can be to set the magnificationtimes by the MCU programmed easily. THS7002I amplified the two-stage input signal, thenoise of amplification is small, magnification precise meanwhile circuit simple structure,easy to debug.(3)Select the active Gaussian shaping circuit which will produce poles of a pair ofconjugate complex through theoretical calculation reasonable configuration componentparameters of the active Gaussian shaping circuit. Compared with the traditional RCshaping circuit it have the better filter forming effect, cascading the two-stage Gaussianshaping circuit in the design, the output waveform is approximately Gaussian waveform, toachieve the better signal-to-noise ratio.(4)Use the method of DC component extraction and addition and subtractionarithmetic to deal with the fluctuation of the baseline, the baseline restorer in this design isbetter than the traditional two-diode baseline restorer which structure is simpler than thegated baseline restoration, to avoid the complexity gated and the baseline restorationachieved more satisfactory results.(5)Determining the peak by the hysteretic comparator, and respectively connected thepeak hold circuit input and output signals to the inverting and positive input of thehysteretic comparator. The hysteresis comparator output high level control signal afterreach peak. Compared with the traditional method of active differential and zero-crossingcomparative, such searching peak methods which circuit is simple, reliable, and canreduce the sensitivity of the comparator, increase the anti-interference ability and preventhysteretic comparator make wrong judgments of the peak due to interference throughsetting parameters of the hysteretic comparator.After improved, energy resolution of the new multi-channel gamma spectrometerreached3.25%(0.660MeV gamma rays of137Cs) through the test, achieved the desiredresults.

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CLC: > Industrial Technology > Nuclear technology > Particle detection,radiation detection and nuclear instrumentation > Radiation detection technology and instrumentation > Spectrometer
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