X-ray Diffraction Tomographic Imaging and Reconstruction

Material discrimination based on conventional or dual energy X-ray computed tomography (CT) imaging can be ambiguous. X-ray diffraction imaging (XDI) can be used to construct diffraction profiles of objects, providing new molecular signature information that can be used to characterize the presence of specific materials. Combining X-ray CT and diffraction imaging can lead to enhanced detection and identification of explosives in luggage screening. In this work we are investigating techniques for joint reconstruction of CT absorption and X-ray diffraction profile images of objects to achieve improved image quality and enhanced material classification. The initial results have been validated via simulation of X-ray absorption and coherent scattering in 2 dimensions.U. S. Department of Homeland Security (2008-ST-061-ED0001

Twins and their boundaries during homoepitaxy on Ir(111)

The growth and annealing behavior of strongly twinned homoepitaxial films on Ir(111) has been investigated by scanning tunneling microscopy, low energy electron diffraction and surface X-ray diffraction. In situ surface X-ray diffraction during and after film growth turned out to be an efficient tool for the determination of twin fractions in multilayer films and to uncover the nature of side twin boundaries. The annealing of the twin structures is shown to take place in a two step process, reducing first the length of the boundaries between differently stacked areas and only then the twins themselves. A model for the structure of the side twin boundaries is proposed which is consistent with both the scanning tunneling microscopy and surface X-ray diffraction data.Comment: 13 pages, 11 figure

X-ray diffraction study of cadmium hydroxyapatite

Solid solutions of cadmium and calcium hydroxyapatite [Ca10−x Cdx (PO4)6 (OH)2 (0 ≤ x ≤ 10)] were synthesized by a wet process in a basic medium. The lattice dimensions of these compounds vary linearly with the atom percent cadmium. The distribution of the calcium and cadmium ions between two non- equivalent crystallographic sites, (1) and (2), were determined by the Rietveld method. The site-occupancy factors of atoms indicate a slight preference of cadmium for site (2) in the apatite structure

X-ray powder diffraction of high-absorption materials at the XRD1 beamline off the best conditions: Application to (Gd,Nd)5Si4 compounds

Representative compounds of the new family of magnetic materials Gd5-xNdxSi4 were analyzed by X-ray diffraction at the XRD1 beamline at LNLS. To reduce X-ray absorption, thin layers of the powder samples were mounted outside the capillaries and measured in Debye-Scherrer geometry as usual. The X-ray diffraction analyses and the magnetometry results indicate that the behavior of the magnetic transition temperature as a function of Nd content may be directly related to the average of the four smallest interatomic distances between different rare earth sites of the majority phase of each compound. The quality and consistency of the results show that the XRD1 beamline is able to perform satisfactory X-ray diffraction experiments on high-absorption materials even off the best conditions.Comment: 12 pages, 3 figures, 3 table

Simulation Of X-ray Diffraction Pattern Of A Various Kinds Of Natural Zeolite Crystal Using Rietan Program

The simulation analysis of natural zeolite crystal structure have been carried out using RIETAN program. The simulation results provide diffraction pattern of some crystal structure data representing as zeolite materials. There are two sets of input data : First Global parameter : a. parameter to correct the zero-point shift of the diffraction pattern : zero-point error,Z, b. parameter to calculate the background : background parameters. Second : Phase-dependent parameters : a. parameter to adjust integrated intensities :scale factor,S, b. prefered orientation parameters, c. profile parameters :FWHM parameters,d parameters to determine peak position : lattice parameters and e.crystal structure parameters: fractional coordinates. The output data contain some information such as:profile diffraction pattern, R factor, final adjusted parameters and their estimated standard deviations, lattice parameters and unit cell volume, structure parameters, number and weight of each species in the unit cell and density,and summary of reflection such as : hkl, 2 theta, d, observation intensity, calculated intensities and structure factors. These output data provide diffraction patterns for some zeolite phases, i.e. : clinoptilolite, heulandite, mordenite, analcime, phillipsite, chabazite and erionite. Results show that was significant and the application can be used for all kind of zeolites and other crystal materials in general applications. The program can be applied easily and the resulting patterns represent all phases significandly. RIETAN simulation program is expected to help hope that helpful suggestion for all people who are identification and characterisation of zeolites qualitatively

X-ray high-resolution diffraction using refractive lenses

Refractive x-ray lenses have recently been applied for imaging and scanning microscopy with hard x rays. We report the application of refractive lenses in an optical scheme for high-resolution x-ray diffraction, performed at a high brilliance synchrotron radiation source. An experimental proof of principle and a theoretical discussion are presented. In particular, we observe the x-ray diffraction pattern from a two-dimensional photonic crystal with 4.2 µm periodicity, which normally is employed to scatter light in the infrared

X-Ray sum frequency generation; direct imaging of ultrafast electron dynamics

X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved X-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear X-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband X-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor/acceptor substituted stilbene