Neutron total cross section measurements of gold and tantalum at the nELBE photoneutron source

Abstract

Neutron total cross sections of 197 Au and nat Ta have been measured at the nELBE photoneutron source in the energy range from 0.1 -10 MeV with a statistical uncertainty of up to 2 % and a total systematic uncertainty of 1 %. This facility is optimized for the fast neutron energy range and combines an excellent time structure of the neutron pulses (electron bunch width 5 ps) with a short flight path of 7 m. Because of the low instantaneous neutron flux transmission measurements of neutron total cross sections are possible, that exhibit very different beam and background conditions than found at other neutron sources. IntroductionExperimental neutron total cross sections as a function of neutron energy are a fundamental data set for the evaluation of nuclear data libraries. With increasing neutron energy the compound nucleus resonances cannot be resolved anymore and will start to overlap. In the energy range of fast neutrons, which is especially important for innovative nuclear applications, like accelerator driven systems for the transmutation of nuclear waste, the neutron total cross section can be described by optical model calculations (e.g. Au(n,) is an activation standard in dosimetric applications [4]. Precise total cross section data with a targeted uncertainty < 5 % will have a direct impact on future evaluations of neutron induced reactions on Au. Also an overlapping measurement from 200 keV to 2.5 MeV is of interest to check consistency.Tantalum is a non-corrosive metal of importance as a structural material in many nuclear and high-temperature applications, e.g. it is also a component in Reduced Activation Ferritic / Martensitic steels [5]. The fast neutron cross section of tantalum has been evaluated recently [6]. In that work, a careful measurement of the neutron total cross section from several tens of keV to several MeV with an accuracy goal of  1 % has been recommended.

Neutron transmission measurements at nELBE

“…The energy resolution ∆E/E increases in this energy range from 2 • 10 −3 to 8 • 10 −3 (FWHM). The resolution has been improved by reducing the scintillation detector thickness as compared to previous measurements [1,2]. This resolution is sufficient to resolve low lying resonances in light nuclei and for average cross sections that can be compared with optical model calculations.…”

“…The random background can be described by a constant value in time-of-flight. It is mostly dominated by random coincidences due to ambient natural radioactivity whereas the room return background of neutrons is relatively low [1]. Fig.…”

The dispersion in spherical statistical optical potential (SOM) from the interaction of fast neutrons with197Au nucle

“…The present calculated total Integral Cross-Section using SOM for neutron energy scattering on 197 Au nuclei at different energies compared with experimental data[26,27].…”