Paul Evans

We demonstrate interleaved sampling by multiplexing conical subshells within the tomosynthesis and raster scanning a phantom through a 150 kV shell X-ray beam. Each view comprises pixels sampled on a regular 1 mm grid, which is then upscaled by padding with null pixels before tomosynthesis. We show that upscaled views comprising 1% sample pixels and 99% null pixels increase the contrast transfer function (CTF) computed from constructed optical sections from approximately 0.6 line pairs/mm to 3 line pairs/mm. The driver of our method is to complement work concerning the application of conical shell beams to the measurement of diffracted photons for materials identification. Our approach is relevant to time-critical, and dose-sensitive analytical scanning applications in security screening, process control and medical imaging.

To retrieve crystallographic information from overlapping sample volumes requires a high-energy probe using a point detector.

A new approach to parafocusing X-ray diffraction implemented with an annular incident beam is demonstrated for the first time. The method exploits an elliptical specimen path on a flat sample to produce relatively high intensity maxima that can be measured with a point detector. It is shown that the flat-specimen approximation tolerated by conventional Bragg–Brentano geometries is not required. A theoretical framework, simulations and experimental results for both angular- and energy-dispersive measurement modes are presented and the scattering signatures compared with data obtained with a conventional pencil-beam arrangement.

To retrieve crystallographic information from extended sample volumes requires a high-energy probe.

Diffraction data may be measured using approaches that lead to ambiguity in the interpretation of scattering distributions. Thus, the encoding and decoding of coherent scattering distributions have been considered with a view to enabling unequivocal data interpretation. Two encoding regimes are considered, where encoding occurs between the X-ray source and sample, and where the encoder is placed between the sample and detector. In the first case, the successful recovery of diffraction data formed from the interrogation of powder samples with annular incident beams is presented using a coded aperture approach. In the second regime, encoding of Debye cones is shown to enable recovery of the sample position relative to the detector. The errors associated with both regimes are considered and the advantages of combining the two discussed.

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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.