Design And Implementation Of A MVT Nuclear Pulse Spectrum Measurement Circuit With Temperature Calibration Function

It is very important to obtain accurate gamma spectrum for neutron logging technology,nuclear pulse spectrum measurement circuit is the core circuit of signal processing of neutron logging instrument,in this thesis,the MVT digital method is applied to the high-speed nuclear pulse spectrum measurement circuit of neutron logging instrument,the gamma ray energy spectrum information is obtained by sampling longitudinal time information,the energy measurement problem of high speed nuclear pulse in high temperature logging environment is solved.A nuclear pulse spectrum measurement circuit based on MVT method is designed and implemented,the circuit mainly includes DAC threshold setting circuit,FPGA nuclear pulse energy measurement circuit and DSP energy spectrum processing circuit.The software function design of FPGA and DSP is completed,FPGA realizes the energy measurement method based on MVT digitization which includes the functions of multi-threshold voltage digitization,pulse reconstruction and energy calculation,the effect of pulse reconstruction and energy calculation on FPGA is tested by Model Sim function simulation.The traditional MVT method is improved,and the real-time temperature calibration function of TDC is realized.The digital temperature sensor based on the ring oscillator is used to detect the temperature change near the TDC,and then the temperature calibration of the TDC is carried out in real time through the temperature calibration circuit.The necessity of integrating the temperature sensor performance,TDC performance and real-time temperature calibration is verified through the temperature experiment.The high temperature test results show that TDC real-time temperature calibration solves the problem of inaccurate energy measurement in TDC due to the time drift of delay line with temperature at high temperature.^{1 37}C S energy spectrum test and water tank neutron shooting experiment show that the energy linearity of this circuit in the range of0?6.13Me V is great,and the energy measurement results are basically accurate.The circuit can measure the energy of high-speed nuclear pulse without using high temperature and high speed ADC,and the measurement dead time of this method is small,the pulse stacking effect is reduced,and the energy measurement accuracy is improved.This provides a new idea for the gamma spectrum spectrum measurement of neutron logging instrument.