Magnetic X-ray circular dichroism (MXCD) has been measured in a ferromagnetic uranium monosulphide crystal by monitoring the fluorescence signal over the uranium M4.5 edges. Despite sizeable absorption corrections, we have obtained a precise value of the dichroic branching ratio, which is compared with sum-rule predictions. We find that, in contrast to the case of cubic 3d transition metals where the magnetic dipole term (Tz) can be neglected, its contribution to the dichroism signal in the present case is larger than that of the spin polarization, (Sz). The dichroism spectrum is shown to exhibit considerably more structure than those of resonant magnetic diffraction from antiferromagnetic actinide compounds, and is found to be in good qualitative agreement with atomic calculations of 5f2 and 5f3 configurations.

The topic of calcite and aragonite polymorphism attracts enormous interest from fields including biomineralization and paleogeochemistry. While aragonite is only slightly less thermodynamically stable than calcite under ambient conditions, it typically only forms as a minor product in additive-free solutions at room temperature. However, aragonite is an abundant biomineral, and certain organisms can selectively generate calcite and aragonite. This fascinating behavior has been the focus of decades of research, where this has been driven by a search for specific organic macromolecules that can generate these polymorphs. However, despite these efforts, we still have a poor understanding of how organisms achieve such selectivity. In this work, we consider an alternative possibility and explore whether the confined volumes in which all biomineralization occurs could also influence polymorph. Calcium carbonate was precipitated within the cylindrical pores of track-etched membranes, where these enabled us to systematically investigate the relationship between the membrane pore diameter and polymorph formation. Aragonite was obtained in increasing quantities as the pore size was reduced, such that oriented single crystals of aragonite were the sole product from additive-free solutions in 25-nm pores and significant quantities of aragonite formed in pores as large as 200 nm in the presence of low concentrations of magnesium and sulfate ions. This effect can be attributed to the effect of the pore size on the ion distribution, which becomes of increasing importance in small pores. These intriguing results suggest that organisms may exploit confinement effects to gain control over crystal polymorph.

The beamline, which is situated on a bending magnet at ESRF, comprises a unique combination of instrumentation for high-resolution and magnetic single-crystal diffraction. White-beam operation is possible, as well as focused and unfocused monochromatic modes. In addition to an eleven-axis Huber diffractometer, which facilitates simple operation in both vertical and horizontal scattering geometries, there is an in-vacuum polarization analyser and slit system, mirrors for harmonic rejection, sub 4.2 K and 1 Tesla magnetic field sample environment, plus a diamond phase plate for polarization conditioning. The instrumentation developed specifically for this beamline is described, and its use illustrated by recent scientific results.

We have measured the resonance spectrum of glide-plane forbidden x-ray diffraction in hexagonal ZnO as a function of temperature. This is the only method to observe deformations of the electronic states caused by thermal atomic motion. The results provide the first evidence for a complex line shape in the spectrum of thermal-motion-induced scattering and the first observation of a dramatic change in resonance spectrum with temperature. The measurements are in agreement with a phenomenological model, based on a combination of constant ͑most probably dipole-quadrupole͒ and temperature-dependent amplitudes. This model provides a means of separating the two components, including their relative phase.

X-ray imaging techniques that capture variations in the x-ray phase can yield higher contrast images with lower x-ray dose than is possible with conventional absorption radiography. However, the extraction of phase information is often more difficult than the extraction of absorption information and requires a more sophisticated experimental arrangement. We here report a method for three-dimensional (3D) X-ray phase contrast computed tomography (CT) which gives quantitative volumetric information on the real part of the refractive index. The method is based on the recently developed X-ray speckle tracking technique in which the displacement of near field speckle is tracked using a digital image correlation algorithm. In addition to differential phase contrast projection images, the method allows the dark-field images to be simultaneously extracted. After reconstruction, compared to conventional absorption CT images, the 3D phase CT images show greatly enhanced contrast. This new imaging method has advantages compared to other X-ray imaging methods in simplicity of experimental arrangement, speed of measurement and relative insensitivity to beam movements. These features make the technique an attractive candidate for material imaging such as in-vivo imaging of biological systems containing soft tissue.