Separation of the inelastic and elastic scattering in time-of-flight mode on the pinhole small-angle neutron scattering diffractometer KWS-2

To study and control the incoherent inelastic background in small-angle neutron scattering, which makes a significant contribution to the detected scattering from hydrocarbon systems, the KWS-2 small-angle neutron scattering diffractometer operated by the Jülich Centre for Neutron Science (JCNS) at Heinz-Maier Leibnitz Zentrum (MLZ), Garching, Germany, was equipped with a secondary single-disc chopper that is placed in front of the sample stage. This makes it possible to record in time-of-flight mode the scattered neutrons in the high-Q regime of the instrument (i.e. short incoming wavelengths and detection distances) and to discard the inelastic component from the measured data. Examples of measurements on different materials routinely used as standard samples, sample containers and solvents in the experiments at KWS-2 are presented. When only the elastic region of the spectrum is used in the data-reduction procedure, a decrease of up to two times in the incoherent background of the experimentally measured scattering cross section may be obtained. The proof of principle is demonstrated on a solution of bovine serum albumin in D2O.

The Application of Silicon-Filtered Beam in the Validation of Iron Cross Sections by Deep Penetration Experiments

This paper summarizes the issue of the validation of the silicon-filtered neutron beam transport in the deep neutron transport penetration experiment in iron. Iron is an essential structural material important for nuclear technology. The use of a silicon-filtered beam is a very interesting method because some significant peaks occur in the spectrum, helping to study selected wide energy regions during the deep neutron transport in the iron. The detailed characterization of the silicon-filtered beam has been performed in the past as well. Therefore, the input spectrum for the penetration experiments is well-known. The character of the input spectrum is reflecting the fine structure of the silicon cross section in region 1–8 MeV. Based on the agreement between calculated and measured attenuation in groups located within the neutron flux peaks, one can reveal possible problems in neutron transport description. The results are confirming satisfactory agreement of neutron transport description in ENDF/B-VII.1 in the majority of energy regions, while in the interval 4.7–6 MeV, underprediction in attenuation can be observed. This seems to be a consequence of discrepancies in the angular distribution of scattered neutrons. These results constitute an advance to previously performed integral experiments characterizing the neutron transport in iron using 252Cf(s.f) and 235U(nth;fiss).

A detailed study of the high energy neutron flux (15-20 MeV) at NCSR “Demokritos” using a BC501A liquid scintillator

The current study was carried out for neutron beam energies ranging between 14.8 and 19.2 MeV using the 3H(d,n)4He reaction and included neutron/gamma discrimination and neutron monitoring utilizing a BC501A liquid scintillator, followed by a pulse shape discrimination-capable circuit. Tests were conducted in order to determine the characteristics and limitations of the employed experimental setup. The deconvolution of the acquired spectra was performed using the DIFBAS computer code. The algorithm is based on the Bayesian conditional probability,whilethe covariance filter method was employed to calculate the a posteriori neutron flux spectrum along with its covariance matrix.The produced neutron beam proved to be practically monoenergetic for low energy deuterons, while at higher deuteron beam energies, the strong presence of parasitic and scattered neutrons was revealed.

On the Genesis of Artifacts in Neutron Transmission Imaging of Hydrogenous Steel Specimens

Hydrogen-charged supermartensitic steel samples were used to systematically investigate imaging artifacts in neutron radiography. Cadmium stencils were placed around the samples to shield the scintillator from excessive neutron radiation and to investigate the influence of the backlight effect. The contribution of scattered neutrons to the total detected intensity was investigated by additionally varying the sample-detector distance and applying a functional correlation between distance and intensity. Furthermore, the influence of the surface roughness on the edge effect due to refraction was investigated.

Directional reflection of cold neutrons using nanodiamond particles for compact neutron sources

Nanodiamond Particles (NDP) are new candidates for neutron reflection. They have a large scattering and low absorption cross-sections for low-energy neutrons. Very Cold Neutrons (VCN) are reflected from NDP with large scattering angles while Cold Neutrons (CN) have a quasi-specular reflection at small incident angles. A new scattering process has been added in Geant4 in order to examine the directional reflection of CN in an extraction beam made of NDP layer. Impurities in NDP are responsible for the up-scattered neutrons, especially hydrogen which has a large cross-section. Other impurities are also considered in Geant4 in order to produce a more accurate model for NDP scattering. The new scattering process is used to model a possible configuration of target-moderator-reflector in Compact Neutron Sources (CNS). A 13 MeV proton beam striking a beryllium target is chosen. Parahydrogen is placed as a cold moderator in order to produce CN. NDP are placed around the extraction beam for scattering the CN toward the exit of the beam. The results show that CN exiting the extraction beam can be increased thanks to the implemented NDP layer.