| Nuclear technology has been widely used in energy,industry,medical,military and other fields.However,while nuclear technology benefits mankind,it also brings enormous challenges to mankind.In recent years,powerful destructive natural disasters such as earthquakes and tsunamis have occurred frequently,seriously threatening the safety of various nuclear facilities.Radionuclide sources in various fields also have the risk of radioactive leakage or loss due to the damage of the outer shell.These unstable factors may cause tremendous damage and adverse effects on people,environment and society.When radioactive emergencies occur,it is necessary not only to detect internal contamination of personnel and quickly estimate their exposure dose,but also to detect,evaluate and deal with contaminants caused by accidents.In this paper,based on the national major scientific instrument project "Rapid Detection Instrument for Nuclear Radiation Contamination in Human Body in Large Volume",and on the basis of the study of the calibration technology for the detection efficiency of pulmonary gamma-ray contamination,the efficiency calibration of volume source and the rapid detection method of contaminants are studied.The main research contents are as follows:1)In view of the difficulty in making the activity volume standard source,it is difficult to calibrate the efficiency directly with the volume source standard.With the basis of Monte Carlo simulation method,a virtual point source method is proposed.Using MCNP5 software,a lead chamber simulation model is established based on the manufacturer's and self-measured data.The detection efficiency of different kinds of point sources at different heights and volumetric sources is simulated by Monte Carlo method,and the relationship between virtual heights of point sources with different volumetric sources energy is obtained.2)For the detection of pollutants,according to the actual existing conditions,using soil U-Ra source,Th source and K source standard samples with known activity,the actual measurement is carried out,the efficiency calibration is calculated,a variety of efficiency calibration curves are fitted,and the best formula of volume source efficiency calibration curve is selected.Cs-137 point source is used to measure different heights and calculate the efficiency.The calculation results are compared with the simulation results,and the efficiency formulas of volume source ray energy and point source height are obtained.The confidence interval of efficiency formula is 500-1500 keV.When the measuring object is equipped with standard volume source,the efficiency of different energy gamma rays is calibrated by measuring and calculating the efficiency of U-Ra body source,Th volume source and K volume source standard sample,combining with the efficiency calibration curve formula of volume source.When the measuring object is not equipped with standard volume source,combining the efficiency formula of energy of volume source ray and height of point source,the efficiency of point source is measured and calculated.The volume source efficiency of different energy gamma rays is calibrated.3)Based on the platform of MATLAB,the gamma analysis and detection software is compiled.The GUI is used to design the operation interface,which mainly includes energy calibration,efficiency scale,spectral smoothness,background subtraction,peak seeking,peak area calculation,peak analysis and so on.In particular,the peak area calculation and peak analysis are studied and analyzed in detail. |
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