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

Abstract

International audienceThe 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

Study of the 240Pu(n,f) and 237Np(n,f) reaction cross sections at the new experimental area (EAR2) of the CERN n_TOF facility

“…Two exceptions are seen though, for 6 Li and 208 Pb. In the former case, the absorption of a neutron results in the formation of 7 Li which is much more abundant than 6 Li (92.5% as opposed to 7.5%) hence the extremely high cross section, while in the latter case the closed-shell configuration results in a stable nucleus, difficult to be perturbed, hence the small cross section.…”

“…Η λειτουργία των εν λόγω νέου τύπου αντιδραστήρων (4ης γενιάς [2,3] και Σύστημα Οδηγούμενο από Επιταχυντή-ADS [4,5]) ϑα επιτυγχάνεται με την χρήση φάσματος ταχέων νετρονίων, συνεπώς η ακριβής γνώση των ενεργών διατομών σχάσης είναι ύψιστης σημασίας και προτεραιότητας, όπως αντικατοπτρίζεται στην Λίστα Αιτημάτων Υψηλής Προτεραιότητας (High Priority Request List [6]) που έχει ϑεσπιστεί από την Υπηρεσία Πυρηνικής Ενέργειας (The Nuclear Energy Agency-NEA, [7])και τον Οργανισμό Οικονομικής Συνεργασίας και Ανάπτυξης (Organisation for Economic Co-operation and Development-OECD, [8])…”

“…For the reasons and concerns discussed previously, it is of vital importance for the feasibility and sensitivity studies of next generation nuclear reactors to obtain accurate nuclear data on a variety of actinide isotopes, for various neutron-induced reactions at neutron incident energies that range from thermal up to tens of MeV [36]. As an example of the importance of accurate nuclear data, the Nuclear Energy Agency (NEA) [7], a specialised agency within the Organisation for Economic Cooperation and Development (OECD) [8] has introduced the High Priority Request List (HPRL) [6] in which numerous neutron-induced cross-sections are listed for various applications along with their target accuracies.…”