Radiative neutron capture cross section from ${}^{236}\mathrm{U}$

The ${}^{236}\mathrm{U}(n,\gamma )$ reaction cross section has been measured for the incident neutron energy range from 10 eV to 800 keV by using the Detector for Advanced Neutron Capture Experiments (DANCE) $\gamma$-ray calorimeter at the Los Alamos Neutron Science Center. The cross section was determined with the ratio method, which is a technique that uses the ${}^{235}\mathrm{U}(n,f)$ reaction as a reference. The results of the experiment are reported in the resolved and unresolved resonance energy regions. Individual neutron resonance parameters were obtained below 1 keV incident energy by using the $R$-matrix code sammy. The cross section in the unresolved resonance region is determined with improved experimental uncertainty. It agrees with both ENDF/B-VII.1 and JEFF-3.2 nuclear data libraries. The results above 10 keV agree better with the JEFF-3.2 library.

Figure 1

Earlier ${}^{236}\mathrm{U}(n,\gamma )$ cross-section measurements [9, 10, 11, 12] compared with the evaluated nuclear data ENDF/B-VII.1 [16] and JEFF-3.2 [17].

Figure 2

Neutron time-of-flight spectrum of the ${}^{236}\mathrm{U}(n,\gamma )$ measurement with the highly enriched Target-1.

Figure 3

Top panel shows total $\gamma$-ray energy spectra at different multiplicities. The highlighted areas show the cut1 and cut3. Bottom panel shows ${}^{235}\mathrm{U}$ fission events. Red square shows cut2.

Figure 4

Total $\gamma$-ray spectra gated on a neutron resonance at 43.91 eV. Left column shows the total $\gamma$-ray energy spectrum at the resonance (solid line) and in the valley between the resonances (blue stippled area) used for the background subtraction. Right column shows the spectrum after the subtraction of the background (solid line) and the total $\gamma$-ray energy cut applied for the analysis. The multiplicity distribution based on the counts within the cuts are shown in the top panel of the right column.

Figure 5

Multistep cascade spectra and the multiplicity distribution of all observed strong resonances.

Figure 6

Average multiplicity of the resonances with different thresholds and coincidence windows. The resonance number corresponds to energy orderings in Table 2.

Figure 7

${}^{236}\mathrm{U}$ neutron capture cross section.

Figure 8

${}^{236}\mathrm{U}$ neutron capture cross section in unresolved resonance region compared with the theoretical calculation.