Research On Correction Method Of Spectrum Drift Based On State Transition

In the actual measurement process of the digital nuclear spectrometer,due to the influence of external temperature changes and the temperature effect of its own electronic components and other factors,the amplitude of nuclear pulse output by the detector changes,finally,the spectrum line formed after the pulse amplitude statistics drifted.The causes of energy spectrum drift are complex and diverse:the temperature effect of the detector medium;the instability of the high-voltage power supply of the measurement circuit;the photomultiplier tube is affected by the external measurement environment,and its magnification changes;electronic components are affected by temperature changes and eventually cause system instability and other factors will affect the measurement of energy spectrum to varying degrees,and then the phenomenon of spectrum drift occurs,which is not conducive to the qualitative and quantitative analysis of the energy spectrum.The energy spectrum measurement process is a continuous process,that is,the statistical fluctuation process of spectrum line formation.When there is a phenomenon of energy spectrum drift,the characteristic change process of the measurement system is implicit in the statistical fluctuation process.In other words,in the measurement of the energy spectrum,the process of spectrum drift caused by the test conditions is a two-layer random process:one layer is the short-term statistical fluctuation process of the energy spectrum,which shows the instantaneous characteristics of the energy spectrum;the other layer is the transition process of the transient characteristics of the energy spectrum.Therefore,if we can effectively describe the two-layer process of energy spectrum drift,we can closely track the transition process of the system state,determine each instantaneous state,and then complete the correction of drift energy spectrum.In view of the above background,this paper mainly analyzes and studies the energy spectrum drift of the digital energy spectrum measurement system.The main work and achievements are as follows:1.Starting from the working principle and composition of the digital energy spectrum measurement system,the process of nuclear pulses for Gaussian forming and trapezoidal forming,and further amplitude statistics to form an energy spectrum is discussed.The phenomenon of energy spectrum drift in the energy spectrum measurement process is analyzed,which is manifested as the difference of nuclear pulse amplitude.Using MATLAB to achieve different nuclear pulse amplitude input,its Gaussian forming and trapezoidal forming different results.2.The main causes of the energy spectrum drift phenomenon were analyzed:the temperature effect of the detection medium in the scintillator detector,the photomultiplier tube showed a change in gain due to temperature,and the change in the gain of the photomultiplier tube caused by the change in high-voltage power supply.The common correction methods of energy spectrum drift are discussed.3.Based on the Hidden Markov Model,the continuous drift energy spectrum measurement process is discretized into the state transition process of multiple instantaneous energy spectrum,and a state transition model of energy spectrum drift is established.The particle swarm optimization algorithm is used to search for the transition parameters of each transition state to complete the correction of the energy spectrum drift.The temperature drift experimental data is used as an application example to verify the energy spectrum drift correction method based on state transition.4.According to the statistical fluctuation characteristics in the measurement process of the energy spectrum measurement system,MATLAB is used to realize the simulation of the energy spectrum.According to the characteristics of different spectrum drift causes,the drift energy spectrum in the case of linear drift and nonlinear drift are simulated,and the drift energy spectra in different situations are corrected.5.Designed and developed spectrum drift simulation and correction software,written an algorithm program for energy spectrum drift process and energy spectrum drift correction,designed a human-computer interaction interface for energy spectrum drift simulation and energy spectrum drift correction,realized energy spectrum data import,The derivation and adjustment of system parameters simulate the dynamic process of drift energy spectrum formation under various drift conditions.The drift spectrum of ¹³⁷Cs,²²⁶Ra,²³²Th with linear drift and nonlinear drift is corrected by software.