Research On ? Spectrum Analysis Method For NaI-type Whole Body Counter

Whole Body Counter?WBC?is an important equipment to quantitatively evaluate the in-vivo pollution of human body after the intake of radionuclides.NaI-type WBC is the most commonly used WBC,however,its measuring result—the?spectrum—is usually very complex,and difficult to be accurately analyzed by existing methods.To this end,this article carried out the relevant research,not only to improve the existing methods,but also developed two new methods.The specific process and results are as follows:1)Carried out on-site measurement and?spectrum collection in 10domestic nuclear power plants,and also completed a fine digital modeling of one WBC.Based on the collected measured?spectra,the characteristics of NaI-type WBC?spectrum are studied which discovered the forming reason of Low Energy Scattering Peak and the shape of the continuum under full-energy peaks generated by 3 typical inner-contamination nuclides:⁵⁷Co?¹³⁷Cs?⁶⁰Co.2)The method of calculating the continuum under full-energy peaks is improved.the conventional linear or polynomial fitting method is no longer used.the fitting method based on Residual Error function and the non-fitting method based on recursive formula are proposed.The results show that the fitting method is applicable to the single peak condition and the non-fitting method is suitable for the case of multiplets and high continuum count,and the performance is obviously better than the previous method.Not only that,with this fruit and the existing full-energy peak analysis algorithms,the first domestic NaI-type WBC dedicated gamma spectrum analysis software NASAS is also developed,and the experiment found that,compared with Canberra's comme rcial software Genie2000,NASAS's analysis result for low energy nuclides are better.3)The study of?spectrum analysis method using the response matrix is carried out.The response matrix from?-ray being released to be detected is established,and for the first time,the sparseness of the energy spectrum is considered,so the inverse of the spectrum is solved by sparse algorithm.The results show that the bias of the estimated nuclide activity value given by response matrix method is less than 6%compared to the actual value,which is significantly better than the full-energy peak analysis method.4)In addition to quantitative analysis,the anomalous qualitative identification method for NaI type WBC?spectrum is also studied based on the machine learning algorithm.In this part,a large number of measured energy spectrum collected in the field is used as the learning object,and the method,which uses Principle Component Analysis for feature extraction with the Mahalanobis distance as the classifier,is established.The results show that this method is more sensitive with less misidentification compared to these quantitative analysis methods above.The work of this paper makes it possible to improve the accuracy of the NaI-type WBC measurement,and thus to ensure the reliability of this type of equipment to be used in nuclear industry as well as in nuclear accident emergency situations.