Subjects: Nuclear Science and Technology >> Particle Accelerator submitted time 2023-06-18 Cooperative journals: 《Nuclear Science and Techniques》
Abstract： Direct demodulation method (DDM) was applied to reconstruct γ-ray spectra. Boosted Richardson-Lucy iteration was introduced into DDM. Monte Carlo method (here GEANT 4) was proposed to calibrate response function and establish response matrix. First, gauss function was regarded as total energy peak. Spectra line was simulated with nine gauss functions. And afterwards DDM was applied to reconstruct the simulated spectra line and determine peak positions and areas. Compared with original spectra, for case that peak position interval was about 1/3 full width half maximum (FWHM), the error of rebuilding peak position was 2 channels. The rest of peaks could be searched accurately. The relative errors of all peaks’ area were less than 4%. Then, three key factors, including noise, background, response matrix, were discussed. Finally, DDM was applied to calibrate the field NaI gamma spectrometer. The errors of U, Th, K were less than 5%. Comprehensive studies have shown that it is feasible to reconstruct gamma-ray spectra with DDM. DDM can significantly pseudo-improve energy resolution of gamma spectrometer, effectively decompose doublets whose peak potential interval is 1/3 FHWM, and accurately search peak and calculate areas. DDM can restrain noise strongly but is greatly influenced by background. And DDM can improve the accuracy of qualitative and quantitative analysis in combination with the conventional spectrum analysis method.
Subjects: Nuclear Science and Technology >> Particle Accelerator submitted time 2023-06-18 Cooperative journals: 《Nuclear Science and Techniques》
Abstract： In this paper, a genetic-algorithm-based artificial neural network (GAANN) model radioactivity prediction is proposed, which is verified by measuring results from Long Range Alpha Detector (LRAD). GAANN can integrate capabilities of approximation of Artificial Neural Networks (ANN) and of global optimization of Genetic Algorithms (GA) so that the hybrid model can enhance capability of generalization and prediction accuracy, theoretically. With this model, both the number of hidden nodes and connection weights matrix in ANN are optimized using genetic operation. The real data sets are applied to the introduced method and the results are discussed and compared with the traditional Back Propagation (BP) neural network, showing the feasibility and validity of the proposed approach.
Subjects: Nuclear Science and Technology >> Other Disciplines of Nuclear Science submitted time 2023-05-31
Abstract： Tomographic Gamma Scanner (TGS), an advanced γ-ray nondestructive analysis technique, can locate and analyze nuclides in radioactive nuclear waste, and TGS can be categorized into two types: e.g., transmission measurement and emission measurement). Specifically, transmission measurements provide the basis for accurate measurement of nonuniform radionuclide content in TGS scanning. The scan data were obtained using the Monte Carlo tool Geant4 simulation, and 25 voxels were divided into five lengths and five widths in a square barrel. In this study, an encoding cropping algorithm based on draped foot vector judgment was adopted to rapidly calculate the voxel trace matrix within a square bucket of nuclear waste, and the transmission images were reconstructed using ordered subset expectation maximization (OSEM). The results indicated that the cropping speed of the improved coding algorithm was significantly higher than that of the original algorithm, and the relative mean deviation (RMD) and root mean square error (RMSE) between the reconstructed attenuation coefficient and the reference standard value tended to decrease with an increase in the cropped line segments in the voxel; the Pearson correlation coefficient (PCC) tended to converge to 1.0. The image quality evaluation parameters of the high media-density materials were better than those of the low media-density materials in the above three indexes. The reconstruction effect was relatively poor for more complex filling materials. When there were more than 10 cropped line segments in the voxel, the reconstruction data generally tended to be stable. The graphical trimming algorithm can rapidly calculate the trace matrix of the scanned voxels; it exhibits the advantages of speed and efficiency and can serve as a novel method to solve the trace matrix of TGS nuclear waste transmission scans.
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