Abstract
A new array of C6D6 detectors installed at the RPI LINAC Center has enabled the capability to measure neutron capture cross sections above the 847 keV inelastic scattering threshold of 56Fe through the use of digital post-processing filters and pulse-integral discriminators, without sacrificing the statistical quality of data at lower incident neutron energies where such filtering is unnecessary. The C6D6 detectors were used to perform time-of-flight capture cross section measurements on a sample 99.87% enriched iron-56. The total-energy method, combined with the pulse height weighting technique, were then applied to the raw data to determine the energy-dependent capture yield. Above the inelastic threshold, the data were analyzed with a pulse-integral filter to reveal the capture signal, extending the the full data set to 2 MeV.
Highlights
Background subtractionThe time-dependent photon background associated with the LINAC beam is attributable primarily to 2.2 MeV γ -rays emitted in 1H(n, γ )2H events occurring in the aqueous target moderator, as well as 1–2 MeV photons emitted in the de-excitation of 181Ta in the target itself [14]
This method, known as the pulse height weighting technique (PHWT), corrects the detectors’ response functions R(Ed, Eγ ) using a weighting function W (Ed ), which is determined via experimental measurements and MCNP simulations of the pulse height spectra for a number of different photon energies [7, 9, 10]
Because lead has a very low capture cross section, and because the detector system’s sensitivity to scattered neutrons was found to be negligible based on prior MCNP simulations and scattering measurements performed with lead and carbon [2], it was assumed that the detected signal from the lead sample was attributable solely to in-beam photons scattering into the detectors
Summary
Modern computational tools have enabled scientists and engineers to perform faster, higher-fidelity simulations of nuclear systems than ever before. The validity of these simulations is constrained by the quality of the nuclear data they incorporate. The upper energy limit for existing capture cross section evaluations in the resolved resonance region of its major isotope, iron-56, has historically been constrained by the first inelastic threshold at 847 keV. The data acquisition system is fully-digitized and saves each individual event for off-line processing and analysis. This allows one to apply energy filters and discriminators to regions of the data affected by inelastic scattering without
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