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

A measurement was performed at the white neutron source Geel Linear Accelerator (GELINA) of the Institute for Reference Materials and Measurements to determine the cross sections for the ($n$, $n^{\prime }\gamma$) and ($n$, $2n^{\prime }\gamma$) reactions on ${}^{56}\mathrm{Fe}$. The Gamma Array for Inelastic Neutron Scattering (GAINS) was used. The results are scaled to the neutron-induced fission cross section of ${}^{235}\mathrm{U}$. The paper emphasizes the multiple checks performed to assure the consistency of the results. $\gamma$ production cross sections, total inelastic cross sections, and level production cross sections were determined. A good agreement exists with previous measurements. Theoretical calculations were performed with the talys 1.6 reaction code using default parameters, but also using a microscopic approach. These calculations are discussed in comparison to the experimental data.

Figure 1

Efficiency of one of the HPGe detectors. The black points represent the experimentally measured efficiency using a calibrated ${}^{152}\mathrm{Eu}$ source. The red line shows the result of an mcnp simulation of a point-like source and the green line display the results of the mcnp simulation for an extended ${}^{56}\mathrm{Fe}$ sample.

Figure 2

Relative uncertainties and correlation matrix for the total inelastic cross section.

Figure 3

Comparison of the spectrum obtained with the iron and with a nickel sample for the energy region around the main $\gamma$ line from ${}^{56}\mathrm{Fe}$. The Ni data were scaled to compensate for a different target thickness and acquisition time.

Figure 4

(a): Comparison of the cross section of the strongest $\gamma$ transition in ${}^{206}\mathrm{Pb}$ obtained with various setups. “GAINS” denotes the result obtained with the present setup. The curves named “Digitizer” and “Conventional” were obtained with the previous setup (only 4 HPGe detectors in a horizontal plane) readout by a conventional and a digitized acquisition, respectively. (b): The $\gamma$ production cross section of the strongest transition in ${}^{56}\mathrm{Fe}$ obtained with various sample thicknesses.

Figure 5

Total neutron cross section on ${}^{56}\mathrm{Fe}$: Comparison of the talys 1.6 calculations using the default and the microscopic approach with experimental data from Refs. [41, 42].

Figure 6

Integral production cross section for the 846.8 keV $\gamma$ ray compared to several previous measurements. ORNL-1971, ANL-1976, ORNL-1990, LANL-2004, and HZDR-2014 label the results presented in Refs. [8, 9, 10, 11, 12], respectively. The gray band from panel (b) represents the uncertainties of our measurement.

Figure 7

Integral production cross section for the $\gamma$ rays from the ${}^{56}\mathrm{Fe}$($n$, $n^{\prime }\gamma$)${}^{56}\mathrm{Fe}$ reaction.

Figure 8

Integral production cross section for the $\gamma$ rays from the ${}^{56}\mathrm{Fe}$($n$, $n^{\prime }\gamma$)${}^{56}\mathrm{Fe}$ reaction.

Figure 9

Integral production cross section for the $\gamma$ rays from the ${}^{56}\mathrm{Fe}$($n$, $2n\gamma$)${}^{55}\mathrm{Fe}$ reaction.

Figure 10

The ratio between the differential cross section of the 846.8-keV $\gamma$ ray measured at ${110}^{\circ }$ and ${150}^{\circ }$ compared to the values calculated based on the angular distributions from Ref. [9].

Figure 11

Total neutron inelastic cross section of ${}^{56}\mathrm{Fe}$. Panel (b) compares the total neutron inelastic cross section obtained in the present measurement with the evaluated data and with the talys 1.6 calculations for the full energy range while panel (a) displays the corresponding uncertainties. Below 2.5 MeV the relative uncertainty peaks when the cross section is low. Panels (c) and (d) show a zoom of the $E_n<2$ MeV region. Above $E_n\approx 6$ MeV the observed fluctuations are dominated by counting statistics.

Figure 12

Level cross section for the ${}^{56}\mathrm{Fe}$($n$, $n\gamma$)${}^{56}\mathrm{Fe}$ reaction.