Simulation Of Detection Efficiency ^{13 Nβ + Decay Annihilation γ-γ Accord}

The leak of radioactive water of high temperature and pressurewithin the PWR primary circuit, will not only reduce the capacity factorand influence the normal operation of the nuclear reactors, but alsocaused the nuclear pollution to the environment, with the monitoring datato analyze the operating conditions of primary circuit pressure boundaryis very necessary.This topic is based on the National Natural Science Foundationproject "Study of nitrogen-¹³ leak monitoring energy spectrumcoincidence method of the PWR primary circuit pressure boundary"（Project Grant No.11175083）, on one of the key technologies of highcoincidence detection efficiency methods to research, proposed to takeadvantage of the energy spectrum of the γ-γ coincidence method tomeasure¹³N, with a view to effectively solve the inadequacies of existingmonitoring instruments, at the same time is also is the project smoothimplementation of the necessary protection.We used the Geant4toolkit to build the coincidence detection model,simulated the coincidence detection efficiency of γ-γ photons producedby¹³N annihilation in M-B sampling container, the affect of samplingcontainers of different sizes to the coincidence detection efficiency aswell as different energy spectrum coincidence monitoring devices modelto the coincidence detection efficiency of annihilation γ-γ photons in the same volume of sampling container, those detected by the NaI（Tl）detectors. And Origin software was used to process the calculatedsimulation data, then analyzed and discussed the detection efficiency andthe counting rate under different conditions. The results showed that, γ-γcoincidence detection technology can make the instrument detection limitto reduce two orders of magnitude, can effectively solve the deficiency ofthe existing¹³N monitoring instrument. For different sizes of thesampling containers, the detection efficiency decreases with the increaseof volume of the container, the count rate increases as the containervolume increases, so on the premise of meet the requirements ofmonitoring indicators, we should integrated design the size of thesampling containers; for different energy spectrum coincidencemonitoring device model, the detection efficiency of the coincidencedetectors external is higher than the efficiency of the built-in, whichprovides a theoretical basis for our prototype production andexperimental verification of the next.