| With the development of modern science and technology,nuclear technology has gradually been widely used.In various nuclear technology applications such as nuclear physics research,radiology and environmental monitoring,it is often required to measure the intensity and energy of gamma rays.Portable gamma spectrometers have become one of the mainstream types of modern conventional energy spectrum analyzers.The stability and accuracy of the portable gamma spectrometer used in the field environment are affected by the ambient temperature.In this context,the γ energy spectrometer based on the NaI(T1)scintillator detector is designed to stabilize the spectrum,and a portable γenergy spectrum that can accurately identify nuclides at an ambient temperature of-35℃to 60℃ is developed.instrument.This thesis first introduces the basic principle of the γ energy spectrum of the detector composed of NaI(T1)scintillator and photomultiplier tube,and analyzes the factors that cause the temperature drift of the energy spectrum curve of the γ spectrometer:the luminous efficiency of NaI(T1)crystal,photomultiplier The multiplication of the tube,high voltage and the gain of the amplifier circuit,etc.On this basis,the program of stabilizing the spectrum of the γ energy spectrometer is elaborated,and the software design and test results of the portable γ energy spectrometer are explained in detail.The main research work of the thesis is as follows:(1)Design the hardware and software circuit of the portable gamma spectrometer based on the NaI(T1)scintillator detector,and develop the nuclide identification and temperature compensation procedures.Including the detector output circuit,power supply circuit,linear amplifier circuit,peak hold circuit,ADC circuit and single chip peripheral circuit.Adopt AD7482 to carry on the analog-to-digital conversion of the peak hold signal,use STM32F446 single-chip microcomputer for data acquisition and calculation,and use the host system based on Linux system.A software interface for adjusting high voltage and adjusting gain is reserved in the circuit,and a nuclide identification program and a temperature compensation program are written in the host.By adjusting the circuit parameters through the host program,automatic spectrum stabilization can be achieved in different environments.(2)The performance of the analog multi-channel analysis circuit is optimized,the energy range of the portable gamma spectrometer is expanded,and the pulse count rate is improved.In the peak hold circuit,strictly design the timing of each part of the circuit,select low-latency devices,and increase the maximum pulse count rate of the peak hold circuit to 1MHz.The output ripple of the power module is reduced by the filter circuit,and a hysteresis comparator with strong anti-interference ability is designed to realize pulse discrimination,and the nuclide energy range of the gamma spectrometer is expanded to 30keV～3.0MeV.(3)On the basis of strictly conducting temperature experiments on the NaI(T1)scintillator portable γ-ray spectrometer,a temperature compensation scheme of high voltage and gain combined control is proposed to realize the identification of low temperature drift nuclide.Using the high and low temperature experimental device,the ambient temperature is in the range of-35℃ to 60 ℃,a large number of experimental studies of the energy spectrum curve with temperature were carried out,and it was found that the spectral drift of the γ energy spectrometer showed a nonlinear relationship with the temperature change.A temperature compensation scheme for the joint adjustment of high voltage and gain was designed,and related compensation procedures were designed to improve the spectral stability accuracy,and the drift ratio was controlled within 1%.The low-temperature drift portable gamma spectrometer based on NaI(T1)detector developed in this paper has been mass-produced,and it is stable and reliable for a long time,easy to carry,and can work in the extreme temperature environment in the field. |
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