Neutron capture cross section measurement ofU238at the CERN n_TOF facility in the energy region from 1 eV to 700 keV

Abstract

F. MINGRONE et al.PHYSICAL REVIEW C 95, 034604 (2017) The aim of this work is to provide a precise and accurate measurement of the 238 U(n,γ ) reaction cross section in the energy region from 1 eV to 700 keV. This reaction is of fundamental importance for the design calculations of nuclear reactors, governing the behavior of the reactor core. In particular, fast reactors, which are experiencing a growing interest for their ability to burn radioactive waste, operate in the high energy region of the neutron spectrum. In this energy region most recent evaluations disagree due to inconsistencies in the existing measurements of up to 15%. In addition, the assessment of nuclear data uncertainty performed for innovative reactor systems shows that the uncertainty in the radiative capture cross section of 238 U should be further reduced to 1-3% in the energy region from 20 eV to 25 keV. To this purpose, addressed by the Nuclear Energy Agency as a priority nuclear data need, complementary experiments, one at the GELINA and two at the n_TOF facility, were proposed and carried out within the 7th Framework Project ANDES of the European Commission. The results of one of these 238 U(n,γ ) measurements performed at the n_TOF CERN facility are presented in this work. The γ -ray cascade following the radiative neutron capture has been detected exploiting a setup of two C 6 D 6 liquid scintillators. Resonance parameters obtained from this work are on average in excellent agreement with the ones reported in evaluated libraries. In the unresolved resonance region, this work yields a cross section in agreement with evaluated libraries up to 80 keV, while for higher energies our results are significantly higher.

Evaluation of cross sections for neutron interactions with 238U in the energy region between 5 keV and 150 keV

“…The average capture cross section σ γ was derived by combining the capture data used by Carlson et al [4] with those of Ullmann et al [9], Kim et al [10], Mingrone et al [11] and Wright et al [12].…”

“…The 238 U(n, γ) cross section data of Ullmann et al [9] and Wright et al [12] result from measurements with a total absorption detector. Kim et al [10] and Mingrone et al [11] applied the total energy detection principle using a set of C 6 D 6 liquid scintillators in combination with the pulse height weighting technique.…”

“…Figure 2 compares this cross section with the one of Carlson et al [4], the data of refs. [9][10][11][12] and the cross section derived from the JEF-2.2 library. The present results are very close to the cross section derived from the JEF-2.2 library.…”

“…This shows the need of a new evaluation based on well documented experimental data. The present evaluation includes the results of Derrien et al [8], as well as the capture data obtained from TOF experiments at the LANSCE [9], GELINA [10] and n TOF [11,12] facilities, which were not available for previous evaluation projects.…”

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

“…covering 8 orders of magnitude in energy. Considering that the binning used for these data often reaches 5000 bins per decade [16], we need to solve systems of the size (4×10 4 )×(4×10 4 ), at the very least. Furthermore, the method should be of sufficient generality to make the transition between the spectra N E and N X not only of differently distributed bins, but also of the different number of bins, implying that P should not necessarily be a square matrix.…”