Neutron capture cross section measurements for 238U in the resonance region at GELINA

Abstract

Abstract. Measurements were performed at the time-of-flight facility GELINA to determine the 238 U(n, γ) cross section in the resonance region. Experiments were carried out at a 12.5 and 60 m measurement station. The total energy detection principle in combination with the pulse height weighting technique was applied using C 6D6 liquid scintillators as prompt γ-ray detectors. The energy dependence of the neutron flux was measured with ionisation chambers based on the 10 B(n, α) reaction. The data were normalised to the isolated and saturated 238 U resonance at 6.67 eV. Special procedures were applied to reduce bias effects due to the weighting function, normalization, dead time and background corrections, and corrections related to the sample properties. The total uncertainty due to the weighting function, normalization, neutron flux and sample characteristics is about 1.5%. Resonance parameters were derived from a simultaneous resonance shape analysis of the GELINA capture data and transmission data obtained previously at a 42 m and 150 m station of ORELA. The parameters of resonances below 500 eV are in good agreement with those resulting from an evaluation that was adopted in the main data libraries. Between 500 eV and 1200 eV a systematic difference in the neutron width is observed. Average capture cross section data were derived from the experimental capture yield in the energy region between 3.5 keV and 90 keV. The results are in good agreement with an evaluated cross section resulting from a least squares fit to experimental data available in the literature prior to this work. The average cross section data derived in this work were parameterised in terms of average resonance parameters and included in a least squares analysis together with other experimental data reported in the literature.

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

“…9 with a resolution of 50 bin/decade (i.e., dE/E = 2%). As can be seen, up to 20 keV they substantially agree with the recently published data by Ullmann et al [46] and Kim et al [47], and with the cross section recommended by Carlson et al [12] and by both 034604-11 TABLE IV. Average capture cross section (σ γ ) and total uncertainty from this work, for neutron energy bins between E l and E h .…”

“…238 U(n,γ ) cross section from this work (red dots) compared to the recently published data by Ullmann et al [46] (green triangles) and Kim et al [47] (blue squares), and to the cross section recommended by Carlson et al [12] (blue circles connected by dotted blue line). The evaluated cross sections from JEFF-3.2 (dark green line) and ENDF/B-VII.1 (cyan line) are plotted for comparison.…”

Critical review of CIELO evaluations of n+ 235U, 238U using differential experiments

“…IAEA CIELO 238 U (n,g) cross sections were adopted from Neutron Standards fit [19] and are shown in Figure 4b compared to evaluated JEFF-3.3 cross section. Evaluated reference 238 U (n,g) cross sections within the Neutron Standards are in excellent agreement with newest highaccuracy measurement at JRC Geel [32,33], while the evaluated JEFF-3.3 cross sections are lower in the whole energy range. The difference between both evaluations reaches about 7% around 45 keV.…”

Trends on Major Actinides from an Integral Data Assimilation

“…Assimilation results for 238 U capture are compared with differential measurements 15 and with the "a priori" JEFF-3.1.1, CIELO and JEFF-3.3 evaluation (Figure 2). Posterior uncertainties for assimilation results are in dotted line.…”