An unfolding method for BSS (Bonner Sphere Spectrometer) measurement without using prior information

[Background] During measurement of the Multi-sphere spectrometer, solutions of the current unfolding methods depend on the prior information. However, during some special circumstances, i. e. experimental validation of the deep penetration problem calculation method, the unfolding process needs to be independent of the prior information. [Purpose] This study aims to propose an unfolding method that is independent of the prior information and adaptive to the uncertainties and illness of the unfolding problems, which is essential to validate the computational method for deep-penetration. [Methods] The iterative regularization unfolding method is based on Krylov subspace method. The Lanczos bidiagnolization was applied to calculate orthogonal basis of the Krylov subspaces, and the Tikhonov regularization was applied to suppress the uncertainties contained in the measured data. The regularization parameter was determined by the GCV (Generalized Cross Validation) principle. Therefore, uncertainties and illness of the unfolding problem can be well constrained. [Results] The established method is applied to multi-sphere spectrometer measurement of 241Am-Be neutron spectrum. The unfolded spectrums are compared with the ISO standard solution. The unfolded results with the proposed method agree well with the reference spectrum. Relative error of the unfolded results of the proposed method is 16%, while relative errors of the unfolded results with the GRAVEL and ML-EM methods are 103% and 107% respectively. [Conclusion] Comparing with the current unfolding methods, the proposed method can effectively avoid the “semi-convergence” behavior and achieve better accuracies while large fluctuations contained in the measured counting are suppressed of the ill-conditioned problem.