Papers by Wolfgang Treimer
Journal of Applied Crystallography, Apr 16, 2015
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
Neutrons and Synchrotron Radiation in Engineering Materials Science, 2017
Nature Communications, 2019
The intrinsic magnetic moment of a neutron, combined with its charge neutrality, is a unique prop... more The intrinsic magnetic moment of a neutron, combined with its charge neutrality, is a unique property which allows the investigation of magnetic phenomena in matter. Here we present how the utilization of a cold polarized neutron beam in neutron grating interferometry enables the visualization and characterization of magnetic properties on a microscopic scale in macroscopic samples. The measured signal originates from the phase shift induced by the magnetic potential. Our method enables the detection of previously inaccessible magnetic field gradients, in the order of T cm −1 , extending the probed range by an order of magnitude. We visualize and quantify the phase shift induced by a well-defined square shaped uniaxial magnetic field and validate our experimental findings with theoretical calculations based on Hall probe measurements of the magnetic field distribution. This allows us to further extend our studies to investigations of inhomogeneous and anisotropic magnetic field distribution.
Applied Physics Letters, 2020
Increased electrical conduction with high hole mobility in anti-ThCr 2 Si 2-type La 2 O 2 Bi via ... more Increased electrical conduction with high hole mobility in anti-ThCr 2 Si 2-type La 2 O 2 Bi via oxygen intercalation adjacent to Bi square net
Journal of Applied Crystallography, 2010
The reflectivity functions calculated by Bonse and Hart for a multi-bounce channel-cut single cry... more The reflectivity functions calculated by Bonse and Hart for a multi-bounce channel-cut single crystal, following the 90-year-old theories of Darwin and Ewald, exhibit extremely narrow nearly rectangular profiles. This feature provides ultra-high angular resolution and sensitivity for the double-crystal diffractometers now widely used for the observation of large-scale structures in condensed matter. However, the experimental results are several orders of magnitude poorer than the theoretical prediction, the `wings problem'. The reason for this discrepancy has remained unidentified for more than 40 years, creating problems for both theory and practice. A solution to this problem for neutron diffraction in Si channel-cut crystals is presented here. The results enable nearly theoretical functions of multiple reflectivity to be obtained, demonstrate the remarkable precision of the Darwin and Ewald theories in the range of the wings, and give rise to much improved sensitivity for the...
International Journal of Materials Research, 2010
Using X-ray and neutron radiography and tomography, images of material and component inhomogeneit... more Using X-ray and neutron radiography and tomography, images of material and component inhomogeneities and their development with time can be obtained. Due to their non-destructiveness and non-invasive nature both methods give insight into the function of devices and their decay processes. Fundamentals of X-ray and neutron radiography and tomography are briefly outlined, examples for both techniques are given, their complementarities are highlighted and emerging techniques and frontiers are discussed.
IEEE Transactions on Nuclear Science, 2005
Neutron tomographies were performed in a double crystal diffractometer (DCD) of bent crystal type... more Neutron tomographies were performed in a double crystal diffractometer (DCD) of bent crystal type. The recorded data from this DCD include much more information about the object than in common absorption tomography. This is due to the additional simultaneous registration of absorption, refraction, and small angle scattering of the neutron beam. The information especially of the small angle scattering data was used to reconstruct the two-dimensional image of the sample from its projections and to compare to the results of common absorption data images. For the first time, it was possible to reconstruct images of samples using USANS data only. This new imaging signal offers a number of new possibilities in high resolution non destructive testing.
Applied Sciences
This Special Issue of Applied Sciences, “Advances in Neutron Imaging”, is published at a time whe... more This Special Issue of Applied Sciences, “Advances in Neutron Imaging”, is published at a time when the COVID-19 epidemic is emerging worldwide [...]
Handbook of Advanced Non-Destructive Evaluation
Physics Procedia, 2015
Abstract The evolution of flux trap behavior at low temperature (the intermediate state) in high ... more Abstract The evolution of flux trap behavior at low temperature (the intermediate state) in high purity Lead samples, both in single crystal with orientation and polycrystalline form, is investigated using field cooled (FC) neutron tomography measurements. Reported measurements are carried out for 0∘ and 90∘ sample axis orientation with respect to the external magnetic field. For both Pb single crystal as well as polycrystalline sample development of fringe pattern below T T c (at 5K) is observed. This shows magnetic field trapped within the sample. On increasing the temperature to 7.5 K for T > T c, fringe pattern inside the sample disappears, indicating that the sample attains a normal state. Further comparison of mosaic spread values for Pb crystal and our previously reported Pb crystal indicate the feeble role played by dislocations and / or defects [Phys. Rev. B 85 184522 (2012)]. Interestingly, not only the field cooled superconducting state appears distinct for each sample, dependent on the crystal structure - single crystal or polycrystalline, but also on the applied magnetic field orientation with respect to the crystallographic sample axis.
Fullerenes, Nanotubes and Carbon Nanostructures, 2005
ABSTRACT Poly(styrene) stars (PS)(6)C-60,C- twin-cores (PS)(6)C-60-[Si-(CH3)(2)]-C-60(PS)(6) and ... more ABSTRACT Poly(styrene) stars (PS)(6)C-60,C- twin-cores (PS)(6)C-60-[Si-(CH3)(2)]-C-60(PS)(6) and hybrids (PS)(6)C-60(PTBMA)(6) with paired arms of PS + poly(tertbutylmethacrylate) have been studied in toluene (20degreesC, concentration C = 1-6 wt.%) by small-angle neutron scattering (SANS) at momentum transfer q = 0.001-5 nm(-1). The C-60 stabilize arms' stretched conformation and intensify stars' ordering. While the (PS)(6)C-60 and hybrids formed tiny clusters (particles' number N similar to 10-80, size R-C similar to 50- 100nm), the dimers created massive structures (N similar to 1.10(3), R-C similar to 300 nm) that can be induced by dipolar interaction of C-60 twin-cores.
One of the most important parameters characterizing imaging systems (neutrons, X-rays, etc.) is t... more One of the most important parameters characterizing imaging systems (neutrons, X-rays, etc.) is their spatial resolution. In magnetic field imaging, the spatial resolution depends on the (magnetic) resolution of the depolarization of spin-polarized neutrons. This should be realized by different methods, but they all have in common that a spin-polarizing and spin-analyzing system is part of the resolution function. First a simple and useful method for determining the spatial resolution for unpolarized neutrons is presented, and then methods in the case of imaging with polarized neutrons. Spatial resolution in the case of polarized neutron imaging is fundamentally different from ‘classical’ spatial resolution. Because of π-periodicity, the shortest path along which a spin-flip can occur is a measure of ‘magnetic’ spatial resolution. Conversely, the largest detectable magnetic field (B-field) within a given path length is also a measure of magnetic spatial resolution. This refers to th...
Neutron News Volume 25 • Number 2 • 2014 15 Introduction Neutron radiography and tomography with ... more Neutron News Volume 25 • Number 2 • 2014 15 Introduction Neutron radiography and tomography with polarized neutrons are one of the “hot topics” in the fi eld of neutron research. For fundamental and applied physics, neutron imaging with polarized neutrons has become an important tool for the investigation of the bulk magnetism in materials and especially in the fi eld of superconductivity where a number of new exciting results show the potential of radiography and tomography with polarized neutrons. The fi rst 2D reconstruction of a magnetic stray fi eld of a small permanent magnet using polarized neutrons for imaging was already performed in 1996 at BER II research reactor at Helmholtz Zentrum Berlin [1]. The set up did not differ principally from modern instruments such as “PONTO II.” Present-day instruments use a white beam and polarize neutrons with He3 fi lters, but a spin analysis of transmitted and depolarized neutrons is diffi cult and only a 2D-depolarization behind the sam...
Improving the spatial resolution conditions in a neutron imaging experiment enables the detection... more Improving the spatial resolution conditions in a neutron imaging experiment enables the detection of phase-based contrast in addition to attenuation contrast. Addressing not only the amplitude but also the phase of radiation in an imaging experiment allows for obtaining additional information about the sample. The so-called neutron phase contrast method improves imaging results mainly by edge enhancement which increases the visibility of sub-resolution structures and of low attenuation contrast materials. These effects have been found at high intensity synchrotron X-ray sources before and have been applied to neutron imaging recently. However, the excellent coherence conditions and spatial resolution of imaging instruments at state-of-the-art synchrotron sources can hardly be compared to neutron imaging. Nevertheless, edge enhancement has been found for increased resolution (coherence) conditions in neutron experiments as well. As for X-ray instruments the effects have been explaine...
Applied Sciences
Reducing the size of ambient magnetic flux trapping during cooldown in superconducting radio-freq... more Reducing the size of ambient magnetic flux trapping during cooldown in superconducting radio-frequency niobium cavities is essential to reaching the lowest power dissipation as required for continuous wave application. Here, it is suggested that applying an alternating magnetic field superimposed to the external DC field can potentially reduce the size of trapped flux by supporting flux line movement. This hypothesis is tested for the first time systematically on a buffered chemically polished (BCP) niobium sample before and after high temperature annealing, a procedure which is known to reduce flux pinning. External low-frequency (Hz-range) magnetic fields were applied to the samples during their superconducting transition and the effect of varying their amplitude, frequency and offset was investigated. A few results can be highlighted: The influence of the frequency and magnitude of the AC fields on the flux trapping in the untreated Nb sample cannot be neglected. The trapped flux...
Journal of Imaging
The neutron imaging instrument CONRAD was operated as a part of the user program of the research ... more The neutron imaging instrument CONRAD was operated as a part of the user program of the research reactor BER-II at Helmholtz-Zentrum Berlin (HZB) from 2005 to 2020. The instrument was designed to use the neutron flux from the cold source of the reactor, transported by a curved neutron guide. The pure cold neutron spectrum provided a great advantage in the use of different neutron optical components such as focusing lenses and guides, solid-state polarizers, monochromators and phase gratings. The flexible setup of the instrument allowed for implementation of new methods including wavelength-selective, dark-field, phase-contrast and imaging with polarized neutrons. In summary, these developments helped to attract a large number of scientists and industrial customers, who were introduced to neutron imaging and subsequently contributed to the expansion of the neutron imaging community.
Measurement Science and Technology
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
For several neutron tomography methods, the use of monochromatic radiation is important. In order... more For several neutron tomography methods, the use of monochromatic radiation is important. In order to select a wavelength band from a white spectrum commonly used devices are velocity selectors, choppers and crystal monochromators. We show how a crystal monochromator changes the wellknown L/D-ratio in CT instruments and how it determines the spatial resolution. We calculate the L/D-ratio as convolution integral and prove the results by the experimental determination of the modulation transfer function (MTF) of the used tomography system.
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Papers by Wolfgang Treimer