We present EGS4 Monte Carlo calculations of the spatial distribution of the dose deposited by a single x-ray pencil beam, a planar microbeam, and an array of parallel planar microbeams as used in radiation therapy research. The profiles of the absorbed dose distribution in a phantom, including the peak-to-valley ratio of the dose distribution from microbeam arrays, were calculated at micrometer resolution. We determined the dependence of the findings on the main parameters of photon and electron transport. The results illustrate the dependence of the electron range and the deposited in-beam dose on the cut-off energy, of the electron transport, as well as the effects on the dose profiles of the beam energy, the array size, and the beam spacing. The effect of beam polarization also was studied for a single pencil beam and for an array of parallel planar microbeams. The results show that although the polarization effect on the dose distribution from a 3 cm x 3 cm microbeam array inside a water phantom is large enough to be measured at the outer side of the array (16% difference of the deposited dose for x-ray beams of 200 keV), it is not detectable at the array's center, thus being irrelevant for the radiation therapy purposes. Finally we show that to properly compare the dose profiles determined with a metal oxide semiconductor field emission transistor detector with the computational method predictions, it is important to simulate adequately the size and the material of the device's Si active element.

The polarization of x-rays plays an outstanding role in experimental techniques such as non-resonant magnetic x-ray scattering and resonant x-ray scattering of magnetic and multipolar order. Different instrumental methods applied to synchrotron light can transform its natural polarization into an arbitrary polarization state. Several synchrotron applications, in particular in the field of magnetic and resonant scattering rely on the improvement in the signal/noise ratio or the deeper insight into the ordered state and the scattering process made possible through these polarization techniques. Here, we present the mathematical framework for the description of fully and partially polarized x-rays, with some applications such as linear x-ray polarization analysis for the determination of the scattered beam's polarization, and the Ge K-edge resonant scattering.

Asymmetrically cut crystals are interesting for use in synchrotron radiation monochromators because of their good energy resolution characteristics and their focusing properties. Ray tracing codes, such as SHADOW, are very efficient in the design and development of new optical devices. In order to determine the convenience of using asymmetrically cut crystals for x-ray monochromators, SHADOW has been extended to include these kinds of crystals. The physical approach to ray tracing asymmetrically cut crystals is based on the coexistence of two periodic structures. One of these is the bulk periodic structure of the Bragg planes. Such a structure determines the existence of a rocking curve near the Bragg condition, and is implemented in SHADOW following the Darwin–Prins formalism of the dynamical theory of diffraction. The second periodic structure is a one-dimensional grating on the crystal surface, formed by the truncation of the lattice planes with the surface. This grating is responsible for the focusing properties of these crystals and plays an essential role in determining the trajectory of the rays. The combination of an asymmetric crystal and a nonplanar surface can be easily achieved by bending (Johann case) to provide improved properties. More complex cases such as the ground-bent crystals (i.e., Johansson geometry) can be considered as a particular case of asymmetrical crystals in which the angle between the Bragg planes and the surface change along the crystal surface. All these cases have been implemented in SHADOW.

Section topographs recorded at different spatial locations and at different rocking angles of a highly oriented pyrolytic graphite (HOPG) crystal allow three-dimensional maps of the local angular-dependent scattering power to be obtained. This is performed with a direct reconstruction from the intensity distribution on such topographs. The maps allow the extraction of information on local structural parameters such as size, form and internal mosaic spread of crystalline domains. This data analysis leads to a new method for the characterization of mosaic crystals. Perspectives and limits of applicability of this method are discussed

The performance of a diamond double-crystal monochromator for the TROIKA II station at the ESRF was studied. Two (111) oriented diamond crystals for Bragg geometry (120 µm and 500 µm thick) were combined in a nondispersive horizontal scattering geometry and characterized in the white Troika undulator beam. The observed rocking curves were slightly broadened due to nonuniform defect distributions present in the crystals. No heat-load-induced broadening was found. The measured reflectivities compared well to the calculated values, and it was shown that a doublecrystal Bragg monochromator can replace a single-reflection Laue monochromator without loss in flux.