Research On Temperature Drift Correction Technology Of NaI(Tl) Spectrometer

In today’s world,nuclear science and technology have penetrated into every aspect of our lives.It has its presence in the fields of medicine,industry,agriculture,etc.It shows that the development of nuclear science and technology plays an indispensable role in the progress of human civilization.Although nuclear science and technology continue to benefit mankind,the situation of nuclear proliferation is not optimistic,such as the illegal transfer of radioactive nuclear materials,nuclear reactor monitoring of nuclear reactor projects and their facilities,and so on for customs cargo security inspections and nuclear power plants.In various challenges,the International Atomic Energy Agency(IAEA)has also long been committed to improving the monitoring technology of radioactive nuclear materials.The monitoring of nuclear radiation is mainly based on the measurement of radioactive energy spectrum.Radioactive energy spectrum measurement technology is widely used,and γ energy spectrum detection technology is suitable for environmental monitoring,ore-seeking,and nuclear reactor decommissioning equipment monitoring.With the popularization of γ-ray spectrum detection technology,various industries have higher and higher requirements for measurement accuracy.To meet the application requirements in various fields,overcoming spectral drift and improving stability is an urgent problem in the development of spectrometers.The paper uses the NaI(Tl)spectrometer to measure the gamma ray spectrum as a target.NaI(Tl)spectrometer uses a large volume of NaI(Tl)crystal with a photomultiplier tube and other electronic components to form a probe.Due to the consistency,stability and uniformity of the crystal itself,the performance parameters are obviously affected by temperature.The magnification of the multiplier tube and the performance of other electronic components are also susceptible to temperature changes.All of the above factors can cause nonlinear drift of the line of the NaI(Tl)spectrometer system,which affects the measurement accuracy.Therefore,the thesis conducts in-depth research,analysis and summary on γ-spectrum measurement technology and γ-spectrum temperature-delay correction method technology at home and abroad.On this basis,the research on the temperature drift correction technology of NaI(Tl)spectrometer was carried out.The formation principle of the instrument spectrum of NaI(Tl)spectrometer and the cause of the drift of the instrument spectrum were analyzed in detail.The drift experiment and the study of the law of temperature drift provide theoretical and data basis for the gamma energy spectrum temperature drift correction method.A large number of experimental data show that the maximum drift of the spectral full-energy peak site of the spectrometer in the temperature range of 10 °C~40 °C can reach ±43 channels(1024 channels),which obviously cannot meet the requirements of high precision measurement.Therefore,this paper mainly summarizes the advantages and disadvantages of several kinds of temperature drift correction methods based on the existing ones,and then proposes a suitable NaI(Tl)spectrometer by analyzing the working characteristics of NaI(Tl)spectrometer and the results of specific experimental data.The temperature drift correction scheme obtains a regular curve between the temperature change amount and the spectrometer magnification.The curve is fitted by the least squares method to establish a mathematical model between temperature and magnification.The temperature acquisition and amplification calculation module is designed.The temperature acquisition is completed by DS18B20 temperature sensor and STM32F103 Z single-chip microcomputer.The temperature value is exchanged with the host computer through MODBUS-RS485 communication through the RS485 converter to complete the data exchange,and then the upper computer software performs the operations on the magnification value: reading,calculating,adjusting,etc.,to correct the spectral line that drifts due to the temperature change.The calibration scheme designed by the thesis does not need to make additional changes to the spectrometer structure,and does not affect the other performance of the spectrometer due to the adjustment of the high voltage,and reduces the damage caused by the reference source correction to the operator,and proves through experiments.This technology can reduce the maximum drift of the spectral full-energy peak address to ±4 channels(1024 channels),effectively reducing the influence of temperature changes on the spectral lines,realizing the temperature drift correction of the spectrometer system,and ensuring that the entire system is safe,stable and reliable.