Energy-selective Neutron Imaging Research Articles

Spectral Characterization of a Velocity Selector Type Monochromator for Energy-Selective Neutron Imaging

The mechanical velocity selector is a device that can be used as wavelength monochromator for energy-selective neutron imaging applications. Its use is desirable in case of moderate wavelength resolution and short exposure times. The resulting beam wavelength distribution is, however, not uniform over the imaging field of view. The effect is inherent to the use of a velocity selector and generated by the change in incident beam's horizontal divergence over the field of view. In this work, the incident beam wavelength change was characterized thoroughly using wavelength scans of iron and vanadium plates and time of flight measurements. Suggestions are made about possible corrections and/or exploitation of this phenomenon-.

Quantification of the material composition of historical copper alloys by means of neutron transmission measurements

Neutron transmission measurements using polychromatic and energy-selective neutron imaging methods were performed with plates of different reconstructed historic copper alloys containing Cu–Sn, Cu–Pb and Cu–Zn. Through comparison with tabulated cross-section values, the alloy component weight fraction could in an accurate quantitative and non-destructive way be retrieved. The results show a good agreement for most of the investigated compositions while the discussion about the remaining discrepancies hints at material inhomogeneities. With this study the way is paved to determine quantitatively in a non-invasive way the composition of unknown historical bronze alloy objects.

Investigation of phase transfer properties of light and heavy water by means of energy selective neutron imaging

We report an investigation of the phase transitions between water and ice using neutron imaging as a research tool. Because of the high scattering cross section of hydrogen for slow neutrons, very small amounts of water can easily be quantified by this technique. However, it is not easy to determine the aggregate state (liquid or solid) if the sample does not have a well defined size, as might happen in the case of water produced in PEM fuel cells. It is important to be able to judge the state of the water (or ice), particularly when it is not easily accessible or hidden by the surrounding structure.The neutron interaction properties of the two aggregates (water and ice) were investigated in dynamic series, in which light water and heavy water were frozen under controlled conditions; transmission images were taken continuously during the phase transition. In addition to the expected density reduction of the ice, some other features were also observed in the images, causing the derived neutron transmission data to differ from the tabulated nuclear data.Energy-selective experiments with thermally stabilized water (+10°C) and ice (−10°C) showed different interaction behaviors for the two aggregates in the neutron wavelength range of 2–6Å. We found clear differences in the absolute values of the attenuation cross-sections and the slopes of their energy dependencies. This result might be used in the future as a criterion to distinguish between the aggregate states in arbitrary water or ice assemblies.

Neutron Visual Sensing Techniques Using the High Intensity Neutron Sources

In this manuscript, the fundamentals and merits of neutron visual sensing techniques, high-speed consecutive visual sensing technique, high-speed-scanning dynamic 3D visualization technique, multi-beam 3D velocimetry technique and energy-selective neutron imaging technique are summarized. These techniques have been developed mainly for the R&D of the nuclear energy system using the high-flux research reactors, JRR-3 and JRR-4, and a high-intensity pulsed neutron source, J-PARC. Very unique visualization and measurement, e.g. dynamic 3D velosimetry in JRR-4 were successfully carried out by these neutron visual sensing techniques. An energy-selective neutron imaging, e.g. the neutron resonance absorption imaging in J-PARC is extremely unique and newly developed visualization and measurement technique. Analytical investigation for the feasibility of multiphase flow experiment in J-PARC was also reported using a Monte Carlo neutron simulation code. It was confirmed from the analytical work that the measurement error of the void fraction of two-phase flow can be reduced by the energy-selective neutron imaging technique.

Energy selective neutron imaging in solid state materials science

Abstract In neutron radiography and tomography, the image contrast is caused by a variation of the effective macroscopic cross-section over the sample volume. Narrowing the energy band of the polychromatic neutron beam in the cold energy range increases the image contrast significantly and opens an access to the crystallographic structure of the sample. Here, we show that crystallographic microstructures of welded stainless steel samples can be visualized and quantified in two and three dimensions by the energy selective neutron imaging. The energy selective neutron radiography maps preferred crystallite orientations over the sample and provides energy values of the highest image contrast. Furthermore, a high contrast neutron tomography visualizes preferred crystallite orientations over the whole macroscopic sample volume.

Energy selective neutron radiography in material research

Energy selective neutron radiography was performed to describe a complex structure in polycrystalline materials. Experiments were performed with currently the highest energy and spatial resolutions achieved simultaneously, by employing a double crystal monochromator for selecting narrow energy bands from the initially polychromatic neutron beam and the neutron absorbing scintillator screen coupled with the cooled CCD camera as a detection system. It was shown that the detailed structure of the welded steel sample can be visualized and quantified by performing energy selective neutron imaging in the cold energy range, where elastic coherent scattering dominates the total cross section of the sample, showing characteristic Bragg edges. With the maps of crystallographic orientations over the sample area of ∼2×2 cm2 and thickness ∼11.2 mm, obtained directly from radiographs, the complex structure was energy resolved with a spatial resolution of ∼50 μm.

Recent improvements in the methodology of neutron imaging

The focus of this article is on further improvements of methods in neutron imaging: the increased spatial resolution for microtomography and options for energy-selective neutron imaging. Before going into details, some common statements are given in respect to the state-of-the-art in neutron imaging. A relation to the X-ray methods is mentioned, where complementary results are obtained. The potential for the energy selection is of particular interest for future installations at the new pulsed sources, based on spallation (SNS, J-PARC, ISIS-TS2). First results from preliminary studies look very promising for future material and industrial research. Therefore, statements about the set-up of the best possible imaging systems are included in the article.

CNR—the new beamline for cold neutron imaging at the Swiss spallation neutron source SINQ

Based on the very good experience and knowledge gained with thermal neutron radiography at NEUTRA, novel capabilities can be predicted for a new beamline with cold neutrons: Micro tomography, neutron phase contrast imaging, contrast enhanced radiography, improved quantification of tracer elements and energy selective neutron imaging. The two main conditions for high-quality neutron imaging—radiography, tomography and especially for neutron phase contrast imaging—are a high beam collimation and a sufficiently high neutron flux. In order to obtain as many cold neutrons as possible from the source, neutron guides are normally used. We have examined whether guides in the accessible parts of the beam channel for CNR could enhance the performance of the instrument. Our findings are (1) that the enhanced divergence provided by the guide is not matched to the collimation or L / D ratio planned for the instrument and (2) the extended image size provided by the guide is not homogeneously illuminated. It has therefore been decided not to use guides inside the target block. The new radiography beam line CNR for imaging with cold neutrons will be installed at channel 52 of the spallation neutron source SINQ. It will have a direct view onto the liquid deuterium cold source. The installation is planned for the annual shutdown period—spring 2005. When operational, the CNR facility will be available for the NR community in the same way as the NEUTRA station.