Development and Verification of the Method for b-Spectrum Decomposition of Radionuclides’ Mixtures Based on Piecewise-Combined Functions with Polynomial or Piecewise-Linear Approximation of their Parameters

Abstract

Development and verification of own method of b-spectrum processing of ultra-low background radiometer-spectrometer Quantulus-1220 with minimal or no sample preparation, with H-3, K-40 and Sr-90+Y-90 presence in liquid sample at various ratio by activity considering quenching. Development of software Aspect-SUBI which implements the method. Materials and Methods. The method is based on deconvolution of the measured b-spectrum in the form of a superposition of model spectra of several radionuclides. b-spectra, obtained from standard radioactive solutions H-3, K-40 and Sr-90+Y-90 mixed with liquid scintillator Optiphase Hisafe 3 in volume ratio 8 ml : 12 ml were used. Methyl orange was used as a quencher. A sum of piecewisecombined functions was used for radionuclide libraries building. The lest squares method was used to determine radionuclide activities in the sample. Computer software Microsoft Excel, Sigma Plot 2000 and R version 4.0.2 was used for statistical processing of findings, their visualization as well as verification of the developed method. Results. Libraries of model b-spectra were built as a sum of piecewise-combined functions with polynomial approximation (library «P») or approximation by piecewise linear functions of their parameters (library «L») depending on quench parameter SQP(E). Verification of interpretation method on paired samples proved its capacity for simultaneous measurement of activity: 1) H-3 (library «P», with relative error ±9%) and K-40 (library «L», with relative error ±20%); 2) H-3 (library «P», with relative error ±11%) and Sr-90+Y-90 (library «L», with relative error ±21%) with limitations due to the levels of activities ratio and strong quenching. At simultaneous measurement of activity K-40 (library «L») and Sr-90+Y-90 (library «L») only correct measurement of activity Sr-90+Y-90 is possible with the error level ±10% taken quench parameter SQP(E) is in the range from 600 to 706. Conclusion. The developed method can be used for simultaneous measurement of volume activity of H-3 and K-40 in urine samples of Ozyorsk population and Mayak PA workers, as well as volume activity of H-3 and Sr-90+Y-90 in samples from Lake Kyzyltash located in the Mayak PA affected area. The developed software Aspect-SUBI can be used not only with Quantulus-1220 but also with any other liquid scintillation spectrometer with logarithmic type of intensification and automatic quench detection.