Michael Drakopoulos

Imaging by parabolic refractive lenses in the hard X-ray range

The manufacture and properties of compound refractive lenses (CRLs) for hard X-rays with parabolic profile are described. These novel lenses can be used up to ∼60 keV. A typical focal length is 1 m. They have a geometrical aperture of 1 mm and are best adapted to undulator beams at synchrotron radiation sources. The transmission ranges from a few % in aluminium CRLs up to about 30% expected in beryllium CRLs. The gain (ratio of the intensity in the focal spot relative to the intensity behind a pinhole of equal size) is larger than 100 for aluminium and larger than 1000 for beryllium CRLs. Due to their parabolic profile they are free of spherical aberration and are genuine imaging devices. The theory for imaging an X-ray source and an object illuminated by it has been developed, including the effects of attenuation (photoabsorption and Compton scattering) and of the roughness at the lens surface. Excellent agreement between theory and experiment has been found. With aluminium CRLs a lateral resolution in imaging of 0.3 µm has been achieved and a resolution below 0.1 µm can be expected for beryllium CRLs. The main fields of application of the refractive X-ray lenses are (i) microanalysis with a beam in the micrometre range for diffraction, fluorescence, absorption, scattering; (ii) imaging in absorption and phase contrast of opaque objects which cannot tolerate sample preparation; (iii) coherent X-ray scattering.

A MICROSCOPE FOR HARD X RAYS BASED ON PARABOLIC COMPOUND REFRACTIVE LENSES

We describe refractive x-ray lenses with a parabolic profile that are genuine imaging devices, similar to glass lenses for visible light. They open considerable possibilities in x-ray microscopy, tomography, microanalysis, and coherent scattering. Based on these lenses a microscope for hard x rays is described, that can operate in the range from 2 to 50 keV, allowing for magnifications up to 50. At present, it is possible to image an area of about 300 μm in diameter with a resolving power of 0.3 μm that can be increased to 0.1 μm. This microscope is especially suited for opaque samples, up to 1 cm in thickness, which do not tolerate sample preparation, like many biological and soil specimens.

Nanofocusing parabolic refractive X-ray lenses

Parabolic refractive x-ray lenses with short focal distance can generate intensive hard x-ray microbeams with lateral extensions in the 100 nm range even at a short distance from a synchrotron radiation source. We have fabricated planar parabolic lenses made of silicon that have a focal distance in the range of a few millimeters at hard x-ray energies. In a crossed geometry, two lenses were used to generate a microbeam with a lateral size of 380 nm by 210 nm at 25 keV in a distance of 42 m from the synchrotron radiation source. Using diamond as the lens material, microbeams with a lateral size down to 20 nm and below are conceivable in the energy range from 10 to 100 keV.

High energy X-ray microscopy for characterisation of fuel particles

Abstract For the first time different high energy microanalysis techniques were combined to characterise individual micrometer sized radioactive particles. It was shown that particle characteristics including weathering rates and mobilisation of associated radionuclides are source specific and release-scenario dependent. Fuel particles released during the explosion are characterised by UO 2 -cores with surrounding layer of reduced U with low weathering rates. In contrast, fuel particles released during the subsequent fire show UO 2 -core with surrounding layers of oxidised U 2 O 5 /U 3 O 8 with high weathering rates

I12: the Joint Engineering, Environment and Processing (JEEP) beamline at Diamond Light Source

JEEP is a high-energy (50–150 keV) multi-purpose beamline offering polychromatic and monochromatic modes. It can accommodate large samples and experimental rigs, enabling in situ studies using radiography, tomography, energy-dispersive diffraction, monochromatic and white-beam two-dimensional diffraction/scattering and small-angle X-ray scattering.

The Use of Small‐Angle X‐Ray Diffraction Studies for the Analysis of Structural Features in Archaeological Samples

X-ray diffraction or scattering analysis provides a powerful non-destructive technique capable of providing important information about the state of archaeological samples in the nanometer length scale, Small-angle diffraction facilities are usually found at synchrotron sources, although the potential of a laboratory source is also described. Specific examples of analysis using X-ray diffraction of historic parchment, archaeological bone, a Central Mexico style pictograph and microdiffraction of calcified tissues are used to show the scope and versatility of the technique, Diffraction data is capable of giving fundamental structural information as well as quantifying the remodelling of structures influenced by environmental factors.

Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves

Zeolites are microporous crystalline materials that find wide application in industry, for example, as catalysts and gas separators, and in our daily life, for example, as adsorbents or as ion exchangers in laundry detergents. The tetrahedrally coordinated silicon and aluminium atoms in the zeolite unit cell occupy the so-called crystallographic T-sites. Besides their pore size, the occupation of specific T-sites by the aluminium atoms determines the performance of the zeolites. Despite its importance, the distribution of aluminium over the crystallographic T-sites remains one of the most challenging, unresolved issues in zeolite science. Here, we report how to determine unambiguously and directly the distribution of aluminium in zeolites by means of the X-ray standing wave technique using brilliant, focused X-rays from a third-generation synchrotron source. We report in detail the analysis of the aluminium distribution in scolecite, which demonstrates how the aluminium occupancy in zeolites can systematically be determined.

Microfocus small angle x-ray scattering reveals structural features in archaeological bone samples: Detection of changes in bone mineral habit and size

Microfocus X-ray scattering provides a powerful nondestructive technique capable of providing important information about the size, habit, and arrangement of mineral crystals in bone. The technique is capable of probing textural differences in a sample at a micron scale resolution. The study presented here involved the analysis of a number of archaeological bones by microfocus X-ray scattering at the ESRF Grenoble in order to determine local changes in mineral durability. The results showed that regions of bone with a modified microscopic morphology contained a greater dispersion of crystal shape when compared with more intact regions and control contemporary bone samples, but the crystal thickness values showed similar consistency. We speculate that the persistence of collagen in the archaeological bone may allow diagenetic remodeling of bone in terms of crystallite shape but defines the size of remodelled crystallites. The ability to detect such local changes in texture has wide potential for determining crystal characteristics in healthy and diseased bone samples.

Ammonia-rich high-temperature superconducting intercalates of iron selenide revealed through time-resolved in situ X-ray and neutron diffraction.

The development of a technique for following in situ the reactions of solids with alkali metal/ammonia solutions, using time-resolved X-ray diffraction methods, reveals high-temperature superconducting ammonia-rich intercalates of iron selenide which reversibly absorb and desorb ammonia around ambient temperatures.

Micro-heterogeneity study of trace elements in USGS, MPI-DING and NIST glass reference materials by means of synchrotron micro-XRF

Synchrotron μ-XRF (X-ray fluorescence analysis), a trace level micro analytical method, allows the quantitative study of the nature and degree of heterogeneity of inorganic trace constituents in reference materials with a homogeneous matrix. In the present study, glass materials of NIST, MPI-DING and USGS containing trace levels of heavy metals are considered. The measurements involve an extensive series of local analyses, performed in identical conditions at different locations on the material. This procedure is employed to measure the degree of micro-heterogeneity of several existing reference materials and to evaluate their suitability for calibration of trace-level micro-analytical methods. For a number of the trace elements present in the various reference materials, a minimum representative mass for homogeneous measurements is calculated.