Research On Key Technologies Of On-line Measurement Of Radioactive Soil Gamma Spectrum

With the application and development of nuclear energy and nuclear technology,a large amount of radioactive waste is generated,which poses a great threat to the environment on which humans depend.Among these radioactive wastes,radioactive contaminated soil has the characteristics of large polluted volume,varying degrees of pollution,and great potential harm.Therefore,the rapid measurement of radioactive soil,which separates out the parts with extremely low radioactivity and little harm to humans,is particularly important to reduce the amount of contaminated soil.Most of the radioactive soil testing instruments are laboratory testing instruments,and the measurement time are long,which cannot meet the requirements of rapid on-site measurement of a large amount of contaminated soil.In response to this phenomenon,this paper conducts a study on the online measurement technology of radioactive soil.The research mainly focused on the theoretical calculation of the detection limit of low radioactive soil,the accuracy analysis of the measurement data,and the technical study of online measurement methods.Research on energy spectrum pretreatment,online measurement influencing factors analysis,nuclide identification and quantitative analysis.?1?The detection limit theoretical calculation obtained the law that the detection limit changes with the background,detection efficiency and measurement time.In order to meet the detection limit of ¹³⁷Cs?100Bq/kg?,methods and techniques for reducing background,joint measurement mode,and improving detection efficiency were studied.Among them,the purpose of reducing the background is achieved by shielding the lead chamber;the joint measurement mode measurement mode is realized by the combined probe of the sodium iodide detector?Na I??size:40cm*10cm*5cm?&high-purity germanium detector?HPGe?(Compared with 1.33Me V⁶⁰Co,the detection efficiency is 40%,the diameter is 67.7mm and the length is 65.2mm)and the energy spectrum inversion.MCNP simulation obtained the energy response function required for energy spectrum deconvolution,and completed the inversion of the measured energy spectrum by directly modulation method,which improved the accuracy of nuclide identification;by increasing the number of detectors,the detection efficiency of the device was improved.Therefore,the existing spectral line synthesis algorithm is analyzed,and the energy spectra measured by multiple sodium iodide detectors?Na I?are synthesized by the adjacent channel interpolation method.After the synthesis,the peak area of the spectrum full-energy peak is counted.The deviation from the theoretical value is within±1%,and the detection limit of three 2L sodium iodide detectors?Na I?measured in the lead chamber is calculated to be 93.87Bq/kg(@¹³⁷Cs,Gamma spectrum accumulation time is 2s).?2?Combined with the above research,the design and verification experiments of the radioactive soil measurement instrument were completed.Through the combination of physical experiments and MCNP simulation,the accuracy of the energy response function was verified,and the effect of the measured soil thickness and humidity on the detection efficiency was determined.According to the result,the optimal thickness of the tested soil is 5cm from the analysis of experimental data.When the amount of water added to the soil is within 5%,the detection efficiency of⁴⁰K changes within 5%and the correction factor of the effect of soil thickness and humidity on ⁴⁰K detection efficiency a_h and a_w.The radioactive soil measuring device designed in this paper?The whole detector is made up of four 2L Na I detectors and one HPGe detector?is determined when the soil treatment is 10t/h,the soil size is40cm×40cm×5cm,the speed of the soil conveyed by the conveyor belt is9.26cm/s,and the detection limit is calculated to be 74.22Bq/kg(@¹³⁷Cs,,Gamma spectrum accumulation time is 2s),which meets the detection limit of ¹³⁷Cs in the"Classification of Radioactive Waste"Claim.