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- 2015 (5) (entfernen)
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- Comptonstreuung (1)
- Computed tomography (1)
- Computertomographie (1)
- Darkfield imaging (1)
- Grating interferometry (1)
- Magnetic domains (1)
- Neutron imaging (1)
- Neutron tomography (1)
- Neutronentomographie (1)
- Shearing gratings (1)
This paper gives a brief overview on3D imaging of magnetic domains with shearing grating neutron tomography. We investigated the three-dimensional distribution of magnetic domain walls in the bulk of a wedge-shaped FeSi single crystal. The width of the magnetic domains wasanalyzed at different locations within the crystal. Magnetic domains close to the tip of the wedge are much smaller than in the bulk. Furthermore, the three-dimensional shape of individual domains wasinvestigated. We discuss prospects and limitations of the applied measurement technique.
Neutron tomography has been applied to investigate the mechanism of hydrogen assisted cracking in technical iron and supermartensitic steel. Rectangular technical iron block samples showed blistering due to intense hydrogen charging and the tomographic method revealed in situ the spatial distribution of hydrogen and cracks. Hydrogen accumulated in a small region around cracks and the cracks are filled with hydrogen gas. Cracks close to the surface contained no hydrogen. Hydrogenous tensile test samples of supermartensitic steel were pulled until rupture and showed hydrogen accumulations at the notch base and in the plastically deformed region around the fracture surface.
CONRAD-2 is an imaging instrument using low-energy (cold) neutrons. The instrument is installed at the end of a curved neutron guide which avoids the direct line of sight towards the reactor core. This ensures a very low background of high-energy neutrons and. photons at the sample position. The cold neutron beam provides a wavelength range which is suitable for phase-and diffraction-contrast imaging such as grating interferometry and Bragg edge mapping. The instrument is well suited for high resolution imaging due to the high efficiency of the very thin scintillators that can be used for the detection of cold neutrons. An instrument upgrade was performed recently as a part of an upgrade program for the cold neutron instrumentation at HZB. The parameters of the instrument as well as some research highlights will be presented.
The potentials of incoherent X-ray scattering (Compton) computed tomography (CT) are investigated. The imaging of materials of very different atomic number or density at once is generally a perpetual challenge for X-ray tomography or radiography. In a basic laboratory set-up for simultaneous perpendicular Compton scattering and direct beam attenuation tomography are conducted by single channel photon counting line scans. This results in asymmetric distortions of the projection profiles of the scattering CT data set. In a first approach, corrections of Compton scattering data by taking advantage of rotational symmetry yield tomograms without major geometric artefacts. A cylindrical sample composed of PE, PA, PVC, glass and wood demonstrates similar Compton contrast for all the substances, while the conventional absorption tomogram only reveals the two high order materials. Comparison to neutron tomography
reveals astonishing similarities except for the glass component (without hydrogen). Therefore, Compton CT offers the potential to replace neutron tomography, which requires much more efforts.
Als Alternative zur Neutronentomographie wird das Potenzial der Computertomographie (CT) mit inkohärenter Röntgen-Streustrahlung (Compton-Streuung) untersucht. Die gleichzeitige Abbildung von Materialien sehr unterschiedlicher Dichten (Ordnungszahlen) ist eine wiederkehrende Herausforderung für die Radiologie und die Computertomographie mit Röntgenstrahlung. Die Messungen ergeben asymmetrische Projektionsprofile für Sinogramme der Streuintensität. Am Beispiel verschiedener Polymere (Polyethylen, Polyamid, PVC), Glas und Holz wird in den Tomogrammen ein hochaufgelöster 'Comptonkontrast' vergleichbarer Dynamik erreicht, während der simultan gemessene 'Absorptionskontrast' ausschließlich die starken Absorber (Glas und PVC) zeigt. Der Vergleich mit ähnlich auflösender Neutronentomographie zeigt ähnliche Kontraste und eröffnet mithin die Möglichkeit, diese künftig durch Compton-Tomographie im Labormaßstab zu ersetzen.