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Poisson's spot is a diffraction phenomenon producing an intensity maximum at the center of the geometric shadow of circular opaque objects. In an analog of the Poisson spot experiment, we show that a tubular cone of x-rays incident upon a crystalline sample produces diffraction spots or foci, corresponding to Bragg maxima within a transmission shadow. We discuss the beam geometry and the intensity gain recorded at the foci in transmission mode. We describe the geometric growth and decay of the foci over a linear axis with the aid of a movie sequence synchronized with the plotting of a diffractogram. The mean signal of a small central area in each successive camera image provides the intensity data for the diffractogram. © 2010 American Institute of Physics. ͓doi:10.1063/1.3514235͔The characterization and measurement of crystallographic structure are of fundamental importance in many branches of science. Angular dispersive x-ray diffraction 1 employed routinely for such analysis dominates this field. However, the coherently scattered or diffracted x-ray signatures are weaker, by orders of magnitude, in comparison with the interrogating x-ray beam. State of the art commercially available powder diffractometers may employ highly sensitive large-area detectors with high quantum efficiency and low noise operating over relatively long integration periods. 2This conventional approach is not ideal for the development of scanning techniques and direct imaging applications, which would benefit from higher intensity signals, reduced integration periods, and converging diffracted beams. In this paper we report examples of diffraction image sequences, which demonstrate the growth and collapse of x-ray foci along the symmetry axis of a tubular interrogating x-ray beam.3 Our approach embodies an analog, employing x-rays, of the optical phenomenon that produces an intensity maximum, known as Poisson's spot, 4 at the center of the geometric shadow of circular opaque objects. In common with short wavelength Poisson spot techniques employing x-ray zone plates 5 or molecular beams 6 we measure the relative intensity of diffraction maxima at the center of a circular geometric shadow. Unlike these techniques, we employ an annular zone, defined at the intersection of a tubular cone of x-rays and a crystalline sample, enabling constructive on-axis interference to form intense spots or foci. The relative intensity and distribution of the foci correspond to the Bragg maxima determined by the crystalline structure of the sample.Consideration of diffraction patterns composed of individual Debye ring contributions hypothesizes the formation of a Poisson spot analog in Fig. 1. A tubular cone of x-rays with its symmetry axis incident normally upon a planar polycrystalline sample and image plane ͑positioned on the transmission side of the sample͒ will produce a continuum of relatively inclined Debye cones resulting in planar patterns composed of elliptical rings. The resultant circular termini and spot intensity fluctuations are due to rotatio...

We demonstrate depth-resolved materials characterization by scanning a sample through an annular beam of X-rays. We measure Bragg X-ray diffraction from a sample with a planar detector positioned centrally in a circular dark field defined by the annular beam. The diffraction maxima are optically encoded with the position of crystalline phases along this beam. Depth-resolved material phase images are recovered via tomosynthesis. We demonstrate our technique using a heterogeneous three-dimensional object comprising three different phases; cyclotetramethylene - tetranitramine, copper and nickel, distributed in a low density medium. Our technique has wide applicability in analytical imaging and is scalable with respect to both scan size and X-ray energy.

Osteoporosis is clinically assessed from bone mineral density measurements using dual energy X-ray absorption (DXA). However, these measurements do not always provide an accurate fracture prediction, arguably because DXA does not grapple with ‘bone quality’, which is a combined result of microarchitecture, texture, bone tissue properties, past loading history, material chemistry and bone physiology in reaction to disease. Studies addressing bone quality are comparatively few if one considers the potential importance of this factor. They suffer due to low number of human osteoporotic specimens, use of animal proxies and/or the lack of differentiation between confounding parameters such as gender and state of diseased bone. The present study considers bone samples donated from patients (n = 37) who suffered a femoral neck fracture and in this very well defined cohort we have produced in previous work fracture toughness measurements (FT) which quantify its ability to resist crack growth which reflects directly the structural integrity of the cancellous bone tissue. We investigated correlations between BV/TV and other microarchitectural parameters; we examined effects that may suggest differences in bone remodelling between males and females and compared the relationships with the FT properties. The data crucially has shown that TbTh, TbSp, SMI and TbN may provide a proxy or surrogate for BV/TV. Correlations between FT critical stress intensity values and microarchitecture parameters (BV/TV, BS/TV, TbN, BS/BV and SMI) for osteoporotic cancellous tissue were observed and are for the first time reported in this study. Overall, this study has not only highlighted that the fracture model based upon BMD could potentially be improved with inclusion of other microarchitecture parameters, but has also given us clear clues as to which of them are more influential in this role.

This paper presents the first use of a simple novel geometry that enables the measurement of diffractograms from polycrystalline materials through linear translation of a point detector. The geometry is such that intensities from all points around any Debye ring are summed to a single point, and thus coherently scattered X‐rays are harvested efficiently. Data from initial experimental verification of the approach used in transmission mode are presented and the diffractograms compared with their equivalent measured using a pencil beam. Brief discussions of potential modifications in reflection geometry and applications for fibre samples are also provided.