| This paper in the overall goal is in overseas investigation Na I seawater gamma energy spectrum measurement system research and Application on the basis of, the comparative study of new LaBr3 detector and Na I detectors for artificial seawater radioactivity measurements of in situ gamma energy spectrum instrument is feasible and can achieve the performance index and its application technology. In this paper, the use of MCNP program simulation, to determine whether the performance of the sea in our country is able to meet the nuclear power plant in the sea of radioactive conventional measurements and nuclear accident rapid response to the needs of the rescue. The main work of this paper includes the following parts:(1) the 137 Cs and 131 I body source energy spectrum analysis, the simulation results are analyzed, and based on the radioactive source of the body, the study of the law of the radioactive gamma rays, etc., to provide a basis for the detection of gamma rays.(2) the detection efficiency and the minimum detection activity of different sizes of crystal, MCNP simulation of different size of the crystal, the analysis of their detection efficiency and the minimum detection activity.(3) the influence of the thickness of different packaging materials on the detection efficiency and the minimum detection activity, the thickness of the different packaging materials were simulated by MCNP, and the effect of the thickness of the material on the detection efficiency and the minimum detection activity was analyzed.(4) the effect of the other elements in the sea water on the detection results, mainly 40 K.In this paper, the MCNP program is used to set up several models, MCNP simulation for different target species, and finally come to the following conclusions:(1) the detection efficiency of the gamma ray spectrometer is analyzed, and the detection efficiency changes with the change of the energy, and the maximum value is obtained when the energy of the gamma ray is about 216 keV. Obtained by fitting: a=2.746, b=2.329, c=7.743×105, d=2.744, fitting coefficient R2=0.994. The fitting results of empirical expression and simulation results are good.(2) the minimum detection activity of the minimum detectable activity of NaI detectors and LaBr3 detectors have bigger difference, NaI detector of the minimum detectable activity than LaBr3 detectors. This is due to the NaI detector background mainly from seawater 40 K, and LaBr3 detectors in the bottom of the mainly from radiation from its own. There is a certain difference in the minimum detectable activity of the different volume detectors, and the minimum detectable activity decreases with the increase of the volume of the detector.(3) the influence of different packaging materials of the minimum detectable activity, effects of different types of packaging materials on the minimum detectable activity is not the same, so had the greatest influence on the minimum detectable activity, aluminum alloy is bigger than the polyvinyl chloride, polyethylene minimum. The density of the 4 kinds of materials are stainless steel, aluminum alloy, polyvinyl chloride and polyethylene in turn from large to small. Along with the increase of the density of the packing material, the shielding of the material to the gamma ray is stronger, and the influence of the minimum detection activity is bigger. |
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