Cross-section measurements for the ${}^{57}\mathrm{Fe}(n,n\gamma ){}^{57}\mathrm{Fe}$ and ${}^{57}\mathrm{Fe}(n,2n\gamma ){}^{56}\mathrm{Fe}$ reactions

A neutron inelastic scattering experiment was performed on an enriched ${}^{57}\mathrm{Fe}$ sample at the Geel Electron Linear Accelerator neutron source using the Gamma Array for Neutron Inelastic Scattering spectrometer. Several $\gamma$-production cross sections were determined, but the first transition (14.4 keV) could not be detected owing to the steadily increased $\gamma$ background at low energies. Consequently, we use an interplay between experimental data and carefully tuned theoretical calculations to generate the total inelastic cross section.

Figure 1

GAINS, the HPGe-based spectrometer used in the current experiment.

Figure 2

Low-excitation-energy level scheme of ${}^{57}\mathrm{Fe}$ according to Ref. [6]. $\gamma$-production cross sections were determined for the transitions drawn with continuous lines.

Figure 3

Background level in $\gamma$ spectra around 14 keV.

Figure 4

Production cross sections for the $\gamma$ rays emitted following the ${}^{57}\mathrm{Fe}(n,n\gamma )$ reaction. The gray bands in panels (a) and (b) represent total uncertainty limits. Data are compared with the results of a previous measurement [8] and with talys and empire calculations using default parameters.

Figure 5

Production cross sections for the 122.1-keV $\gamma$ ray: comparison of the results obtained using the present ${}^{57}\mathrm{Fe}$-enriched sample (black line), the one obtained in a previous experiment using a ${}^{\text{nat}}\mathrm{Fe}$ target (green line) [3], and the result from Ref. [8] (blue dots). The cross sections obtained with the ${}^{\text{nat}}\mathrm{Fe}$ target are only relative values.

Figure 6

Neutron nonelastic cross section on ${}^{57}\mathrm{Fe}$ calculated with empire, compared to the values from the evaluated libraries JEFF-3.2 and ENDF/B-VII.1.

Figure 7

The impact of the number of discrete levels on the empire calculated production cross sections of the (a) 122.1- and (b) 692.0-keV $\gamma$ transitions. The continuous lines correspond to $N_d=25$ levels, while the dashed ones are obtained using $N_d=100$.

Figure 8

Production cross sections for the $\gamma$ rays emitted following the ${}^{57}\mathrm{Fe}(n,n\gamma )$ reaction. Comparison of the tuned empire calculations with our experimental results. The dashed lines display the calculation results after adjusting the nonelastic cross section but before adjusting the level population cross sections while the continuous lines represent the best-tuned calculations. See the text for details.

Figure 9

846.8-keV $\gamma$-production cross sections from the ${}^{57}\mathrm{Fe}(n,2n){}^{56}\mathrm{Fe}$ reaction. The blue curve displays the raw cross section we measured. The purple line is the ${}^{56}\mathrm{Fe}(n,n\gamma )$ cross section from Ref. [3] scaled for the relative abundance of ${}^{56}\mathrm{Fe}$ and ${}^{57}\mathrm{Fe}$ in our target. The black line represents our final result (together with the gray uncertainty band) compared with the talys default calculation displayed in green and the tuned empire calculations in red.

Figure 10

Level cross sections in the ${}^{57}\mathrm{Fe}(n,n^{\prime })$ reaction. The ranges where our values are strictly correct are listed in Table 2. Above the specified ranges our values represent higher limits of the level cross sections. The experimental results are compared with the evaluated cross sections from ENDF/B-VII.1 and JEFF-3.2 but also with the tuned empire calculations. We note that the JEFF-3.2 evaluation overlaps perfectly with the default talys calculations (not shown here), and the ENDF/B-VII.1 evaluation overlaps with JENDL-4.0 (also not shown).

Figure 11

Total inelastic cross section for the ${}^{57}\mathrm{Fe}(n,n^{\prime })$ reaction (black points), calculated based on the theoretically determined contribution of the 14.4-keV $\gamma$-production cross section (orange line), and the experimental results for the 136.5- (blue line), 366.8- (violet line), 692.0-, and 898.4-keV $\gamma$-production cross sections. The red line shows the total inelastic cross section calculated by empire using the tuned parameters.

Figure 12

Theoretically calculated total inelastic cross section for the ${}^{57}\mathrm{Fe}(n,n^{\prime })$ reaction compared to various evaluations. Both default empire and talys calculations overlap almost completely with the JEFF-3.2 evaluation.