Experiments in the EXFOR library for evaluation of thermal neutron constants

Abstract

Abstract. E.J. Axton's experimental database adopted in evaluation of thermal neutron constants by himself and also by a recent project to update the IAEA Neutron Standard was checked against the experimental literature and EXFOR library. We discovered that many data are found neither in the EXFOR library nor in the articles quoted by Axton due to various reasons. This paper summarizes the status of the experimental data cited by Axton in the experimental literature as well as in the EXFOR library.Cross sections for thermal (2200 m/s) neutrons are fundamental neutron-induced reaction data, which have been evaluated at the IAEA since the pioneering works by Westcott [1], Hanna [2] and Lemmel [3,4]. In a typical evaluation of the thermal neutron constants (TNC) within the current IAEA Neutron Standards [5], 25 constants (elastic, fission and capture cross sections, absorption and fission g-factors, and total fission neutron multiplicities of 233 U, 235 U, 239 Pu and 241 Pu at the thermal energy as well as 252 Cf spontaneous total fission neutron multiplicity) measured both in differential (monoenergetic) and integral (broad spectrum) experiments are included in a simultaneous generalized least-squares analysis by the GMA code [5]. Recent TNC evaluations for update of the IAEA Neutron Standard are based on the comprehensive work by Axton [6][7][8]. However, Axton's experimental database (Table 1 of [8]) contains many data not available in the EXFOR library [9]. We have reviewed Axton's experimental database to identify the data missing in EXFOR and possible experimental corrections.The results are summarized in Table 1, where• "Quantity" gives the quantity given in the Axton's database, where (1) a, f, s, sm and γ stand for absorption, fission, scattering, scattering for rolled metal and capture; (2) 9, 0, 1, 2, 3, 4, 5, 52 for 239,240,241,242 Pu, 233,234,235 U and 252 Cf; (3) σ and η for 2200 m/s cross section and eta,ν for total fission neutron multiplicity,σ andη for Maxwellian spectrum averaged σ and η at T = 20 • C), g is the Westcott a

The joint evaluated fission and fusion nuclear data library, JEFF-3.3

“…2.2.14, 2.2.15). The change implied replacing the data for inelastic scattering to the first level up to 4.5 MeV, to levels 2, 3, 4, 5 and 9 up to 4 MeV and to levels 6, 7 and 8 up to 3.9 MeV with the renormalized experimental data as available in EXFOR [179]. The cross sections above these energies were smoothly matched to the existing evaluated cross sections at 20 MeV by a multiplicative factor depending linearly on the energy (Fig.…”

“…The publications (or, if not available, the EXFOR entries [179]) of thermal cross section experiments are studied in some detail, and the evaluators try to identify experimental uncertainty components which are not included in the experimenters' analyses. Seemingly missing uncertainties are added using assumed default values, which are intended to be somewhat conservative.…”

“…[208]. The unresolved resonance parameters and the neutron cross sections In contrast, the ENDF/B-VII.1 resonance region data is taken from JEFF-3.1 for 174,176,178,180 Hf and JENDL-3.3 for 177,179 Hf, with some adjustments to bound levels, RRR upper limits and URR average parameters. ENDF/B-VIII.0 [180] uses the ENDF/B-VII.1 resonance region data with cross sections and energy spectra above the resonance region produced by Kawano (LANL) using the CoH3 code in 2016.…”

Investigation of Photonuclear Experiments Systematic Uncertainties Using the International Nuclear Reactions Database

“…Они играют большую важную роль в процессах возбуждения и распада гигантского дипольного резонанса (ГДР) ядер, образования элементов во Вселенной, мониторирования сталкивающихся частиц в современных коллайдерах, при решении многих химических, биологических, технических, медицинских и многих других проблем. В этой связи фотоядерные данные занимают заметное место в международной базе данных (БД) системы (EXFOR) по ядерным реакциям [1][2][3][4], созданной и поддерживаемой Сетью Центров данных по ядерным реакциям Международного агентства по атомной энергии (МАГАТЭ) [5].…”

“…Зачастую, даже относительно простая системная обработка известных результатов выявляет принципиально новую физическую информацию, которая ранее отсутствовала (по крайней мере, в явном виде), поскольку для ее выявления не было никаких оснований [8,9]. Настоящий доклад посвящен использованию возможностей международной БД по ядерным реакциям [1][2][3][4] для решения давно и широко известной проблемы существенных расхождений результатов разных фотоядерных экспериментов, обусловленных проявляющимися в них неизвестными систематическими погрешностями. Наличие таких погрешностей и расхождений ставит под сомнение достоверность экспериментальных данных и, по существу, не позволяет использовать один из основных философских принципов («критерий истины -практика»).…”