A direct method for unfolding the resolution function from measurements of neutron induced reactions

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2017-12, Vol.875, p.41-50
• Main Authors: Žugec, P., Colonna, N., Sabate-Gilarte, M., Vlachoudis, V., Massimi, C., Lerendegui-Marco, J., Stamatopoulos, A., Bacak, M., Warren, S.G.
• Format: Article
• Language: English
• Subjects: Cholesky decomposition; Computer Science; Data Analysis, Statistics and Probability; n_TOF facility; Neutron time of flight; Physics; Resolution function; Unfolding
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2017.09.004

The paper explores the numerical stability and the computational efficiency of a direct method for unfolding the resolution function from the measurements of the neutron induced reactions. A detailed resolution function formalism is laid out, followed by an overview of challenges present in a practical implementation of the method. A special matrix storage scheme is developed in order to facilitate both the memory management of the resolution function matrix, and to increase the computational efficiency of the matrix multiplication and decomposition procedures. Due to its admirable computational properties, a Cholesky decomposition is at the heart of the unfolding procedure. With the smallest but necessary modification of the matrix to be decomposed, the method is successfully applied to system of 105×105. However, the amplification of the uncertainties during the direct inversion procedures limits the applicability of the method to high-precision measurements of neutron induced reactions.