Confocal energy-dispersive X-ray diffraction tomography employing a conical shell beam.

A J Dicken,D Prokopiou,K D Rogers,M Wilson,S X Godber,F Elarnaut,A Shevchuk,J P O Evans,D Downes

doi:10.1364/oe.27.019834

Abstract

We introduce a new high-energy X-ray diffraction tomography technique for volumetric materials characterization. In this method, a conical shell beam is raster scanned through the samples. A central aperture optically couples the diffracted flux from the samples onto a pixelated energy-resolving detector. Snapshot measurements taken during the scan enable the construction of depth-resolved dark-field section images. The calculation of d-spacing values enables the mapping of material phase in a volumetric image. We demonstrate our technique using five ~15 mm thick, axially separated samples placed within a polymer tray of the type used routinely in airport security stations. Our method has broad analytical utility due to scalability in both scan size and X-ray energy. Additional application areas include medical diagnostics, materials science, and process control.

Highlights

The high penetration power of X-rays is the basis for projection radiography and X-ray computed tomography
These modalities are highly developed and deployed routinely within security screening, industrial inspection, and medical diagnostics. Within this broad application space, there are many critical spatial imaging tasks, which would benefit from the identification of material phase attributed to components within a volume
This paper describes a tomographic method in which a raster scanning snapshot Focal construct geometry (FCG) probe directly measures XRD sections to enable material specific volumetric visualizations

Summary

Introduction

The high penetration power of X-rays is the basis for projection radiography and X-ray computed tomography These modalities are highly developed and deployed routinely within security screening, industrial inspection, and medical diagnostics. The spectroscopic analysis of transmitted X-rays can provide some useful materials discrimination information [1]. Such methods are limited fundamentally, as the image forming Xrays incident on a detector have propagated along linear paths without interacting with the sample. Traditional XRD instruments or diffractometers may be categorized into either angular [2] or energy dispersive [3,4,5,6] modalities The former employs monochromatic radiation to measure the diffraction angle, 2θ, subtended by the diffracted flux (from a sample) and the primary beam, while the latter measures the energy or wavelength, λ, at a fixed, known diffraction angle. Even with the use of a bright source and carefully prepared samples, the measurement time can range from minutes to hours

Methods

Results

Conclusion