Phase objects are readily imaged through Fresnel diffraction in the hard x-ray beams of third-generation synchrotron radiation sources such as the ESRF, due essentially to the very small angular size of the source. Phase objects can lead to spurious contrast in x-ray diffraction images (topographs) of crystals. It is shown that this contrast can be eliminated through random phase plates, which provide an effective way of tailoring the angular size of the source. The possibilities of this very simple technique for imaging phase objects in the hard x-ray range are explored experimentally and discussed. They appear very promising, as shown in particular by the example of a piece of human vertebra, and could be extended to phase tomography.

/pdf/phase-objects-in-synchrotron-radiation-hard-x-ray-imaging-2vvaht6a7i.pdf

Phase objects in synchrotron radiation hard x-ray imaging

X-ray computed microtomography (μCT) using synchrotron radiation (SR)

Neutron imaging can provide two- or three-dimensional, spatially resolved images of the internal structure of bulk samples that are not accessible by other techniques, making it a unique tool with many potential applications. The method is now well established and is available at neutron sources worldwide. This review will give a survey of the technique of neutron imaging with a special focus on neutron tomography; the basics of the method as well as the technology of instrumentation will be outlined, and the techniques will be illustrated by representative applications. While the first part of the paper focuses on conventional attenuation contrast imaging, the second part reviews and critically assesses recent methodical developments.

https://iopscience.iop.org/article/10.1088/0022-3727/42/24/243001/pdf

Advances in neutron radiography and tomography

Spin-polarized neutrons are sensitive to magnetic fields, and they can relatively easily penetrate through matter A new imaging technique uses these two properties for mapping the three-dimensional distribution of magnetic fields inside massive objects Neutrons are highly sensitive to magnetic fields owing to their magnetic moment, whereas their charge neutrality enables them to penetrate even massive samples The combination of these properties with radiographic and tomographic imaging1,2,3,4 enables a technique that is unique for investigations of macroscopic magnetic phenomena inside solid materials Here, we introduce a new experimental method yielding two- and three-dimensional images that represent changes of the quantum-mechanical spin state of neutrons caused by magnetic fields in and around bulk objects It opens up a way to the detection and imaging of previously inaccessible magnetic field distributions, hence closing the gap between high-resolution two-dimensional techniques for surface magnetism5,6 and scattering techniques for the investigation of bulk magnetism7,8,9 The technique was used to investigate quantum effects inside a massive sample of lead (a type-I superconductor)

/pdf/three-dimensional-imaging-of-magnetic-fields-with-polarized-5e1bj77520.pdf

Three-dimensional imaging of magnetic fields with polarized neutrons

REVIEW ARTICLE: Neutron optics

Imaging of ferromagnetic domains by neutron interferometry

Perfect crystal Laue case (n, – n) rocking curves (i.e. convoluted intrinsic reflection curves) display pronounced oscillations provided both crystals have equal thickness and are rotated exactly through their parallel orientation. It is shown that the oscillations are directly related to the oscillatory structure of the intrinsic curves known from the dynamical diffraction theory, a fact which has been overlooked so far. Experimental oscillatory rocking curves agree very well with calculated curves and can neatly be used to extract the intrinsic distributions. A special feature of the “equal thickness” rocking curves is the extremely narrow central peak. For instance, with the silicon 440 reflection and AgKα X-rays, the central peak is less than 0.05″ of are wide. A possible application is in very sensitive small angle measurements with hard X-rays or thermal neutrons.



Laue-Fall-Rockingkurven (d. h. gefaltete sog. „intrinsic” Idealkristall-Reflexionskurven) zeigen ausgepragte Oszillationen fur den Fall, das beide Kristalle exakt gleiche Dicke haben und genau durch ihre Parallelstellung hindurch gedreht werden. Es wird gezeigt, das die Oszillationen direkt von der Oszillationsstruktur der Idealkristall-Reflexionskurven der dynamischen Theorie herruhren, ein Umstand, der bisher ubersehen wurde. Oszillierende experimentelle Rockingkurven stimmen sehr gut mit berechneten uberein und gestatten, aus ihnen die „intrinsic” Kurven zu ermitteln. Eine einzigartige Eigenschaft der mit zwei gleichdicken Kristallen gewonnenen Rockingkurven ist die auserst scharfe Spitze in der Mitte der Kurve, welche z. B. beim Silizium 440-Reflex mit AgKα-Strahlung weniger als 0,05″ breit ist. Eine mogliche Anwendung ist die Messung der Kleinwinkelstreuung von Rontgenstrahlen und Neutronen mit extremer Auflosung.

W. Graeff

Papers

Imaging of ferromagnetic domains by neutron interferometry

Oscillatory structure of laue case rocking curves

Measuring angular deviations of neutrons of the order of 10−3 sec of arc

On the possibility of measuring the length of X-ray or neutron wave trains with the three-beam case interferometer