Research On Key Parameters Of Seawater Gamma Spectroscopy In Situ Measurement Detector Based On Monte Carlo Simulation

After a major level 7 nuclear leak in Fukushima,Japan,it caused serious damage to the marine environment,and the social panic caused to the international community has continued to this day.my country has built a large number of nuclear power plants in recent years,and a monitoring system that can detect marine radioactive pollution in real time has become particularly important.At present,the main method of marine radioactivity monitoring in my country is to take samples in the key monitored sea areas and bring them back to the laboratory for analysis.This method has a long period and is difficult to provide early warning of radioactive pollution.In-situ gamma spectroscopy measurement of seawater will bring The detection system with detectors is directly placed in the target sea area to continuously monitor the radioactivity data of the sea water in real time.First,the Na I(Tl)detector model was established,and the corresponding Monte Carlo simulation was carried out.After comparing the simulated energy spectrum curve with the actual measured ¹³⁷Cs body source gamma energy spectrum,it can be found that the main characteristics of the simulated energy spectrum,Including the peak position of the all-powerful peak,Compton plateau,scattering peak,etc.are basically consistent with the experimental results,and the simulated detection efficiency and minimum detection activity are consistent with the experimental results.It shows that it is feasible to use Monte Carlo to simulate the in-situ gamma spectrum of seawater.On this basis,the response energy spectra of the common artificial radioactive elements¹³⁷Cs,¹³¹I and ⁶⁰Co seawater sources and point sources were simulated.Comparing the two energy spectra,it can be seen that the low energy end of 73ke V is due to the Compton scattering effect.The dominant position is lost,and a larger scattering peak appears.Secondly,a ¹³⁷Cs point source Na I(Tl)detector model was established,and the relationship between different crystal sizes,different packaging materials,minimum activity and detection efficiency was simulated by Monte Carlo.When the Na I(Tl)crystal size is 4 inches,the minimum detection activity reaches 0.046Bq/L.Any packaging material will have a certain effect on detection.The detection efficiency and minimum detection activity are linearly related to the thickness of the material.The simulation results show that polyethylene is one of the better packaging materials.Finally,in order to solve the problem that radioactive detectors placed too deep or too shallow will be affected by the background radiation of the seabed and the secondary rays of cosmic rays and cosmic rays,a measurement method based on pressurized water buoys was designed,and Build the Monte Carlo model of the buoy.By adjusting the material and thickness of the pressurized water tank,and respectively simulating the minimum detection activity and detection efficiency,it can be concluded that when the material of the pressurized water tank is 20mm tungsten-nickel alloy and the thickness of the pressurized water tank is greater than 2m,the detection efficiency is close to 0.It shows that it has a good shielding effect for ¹³⁷Cs.