The Study Of Coincidence Measuring Method Based On Five Detector

Leakage Monitoring of reactor Primary Circuit pressure Boundary in Nuclear Power Plant is an important part of Nuclear Power Plant radiation Monitoring system.Using ¹³N nuclide as tracer,the quantitative leakage results can be obtained by using low background method to measure the water leakage at the primary pressure boundary,but there is a shortage of high detection limit.The detection limit of the system depends on the measurement background and detection efficiency of the instrument.The use of ¹³N radionuclide decay characteristics using coincidence measurement devices can effectively improve the shortcomings of the existing low background measurement methods.Because the coincidence measurement method can effectively reduce the measurement background.At the same time,because of the coincidence method,the detection efficiency of ¹³N will be reduced.Therefore,it is great significance for the coincidence measurement of¹³N detection method and how to improve the ¹³N detection efficiency forγ-γspectrum coincidence measurement technology.Based on the previous theoretical simulation,the coincidence measurement method is studied experimentally.According to the results of theoretical simulation optimization,four kinds of sampling and detecting devices with different shapes are selected.The coincidence efficiency of the sampling vessel is measured by using five NaI（TI）detectors to form a coincidence detection system.The simulation results are verified by experiments.The coincidence background count and coincidence efficiency of the coincidence detector are measured experimentally.The coincidence efficiency of the four sampling containers is 1.60%、2.66%、2.59%、5.05%.The experimental results are in agreement with the theoretical simulation results in the range of error.In this experiment,five NaI（TI）detectors are used,so it will be more difficult to use the NIM plug-in coincidence circuit.In order to improve the experiment and consider the future application in the nuclear power plant,the multiplex coincidence circuit system is designed,including circuit hardware,single-chip computer software and host computer software.The coincidence efficiency of the detecting device is measured by using the multiplex coincidence circuit system,the results is 1.62%,2.66%,2.60%,5.12%.This is consistent with the experimental results measured by the NIM plug-in,and verifies the correctness of the multiplex coincidence circuit system.Therefore,the multiplex coincidence circuit system can be used to replace the NIM plug-in coincidence circuit in the future.The experimental results in this paper are consistent with the previous theoretical simulation results.The correctness of the theoretical simulation results is verified.It is concluded that four coincidence detectors are located in the sampling container and the radius of the container is 13 cm will be obtained with higher efficiency.