In the past decades several authors have demonstrated the ability of X-Ray Diffraction Imaging (XDI) in providing spatial and material specific information about the object under investigation [I]. Energy Dispersive X-Ray Diffraction (EDXRD) systems detect diffraction patterns by using a polychromatic spectrum and measuring the coherently scattered beam at a specific angle. This type of molecular-specific information plays a key role in security screening modalities providing high detection as well as low false alarm rates [2]. In the past, one of the main limitations to the widespread use of this technology in airport screening was the slow scanning rate compared to conventional systems. With the advent of novel system topologies such as the 3rd Generation energy-dispersive XDI configurations [3], this issue can be overcome [4].In the present work a simulation tool accounting for molecular interference and providing multiple collimation configuration options has been validated with a single source dual-channel geometry. The primary-scatter and cross-scatter signals generated by two neighboring voxels have been studied here, analyzing both coherent and incoherent scatter contributions; and a method for a first order material independent cross-scatter correction has been evaluated. The tool has then been applied for first investigations of a Multiple Inverse Fan Beam (MIFB) concept.
X-ray diffraction imaging (XDi) refers to the volumetric analysis of extended, inhomogenous objects by spatially-resolved x-ray diffraction. Following a brief description of some of the areas in which x-ray diffraction (XRD) is currently impacting on the detection of materials of interest in the security environment, the principles of energy-dispersive x-ray diffraction tomographic systems of the 1 st , 2 nd and 3 rd generation are described. The Multiple Inverse Fan Beam (MIFB) topology for 3rd Generation XDi, in which the XRD properties of a 2-D spatial array of volume elements are investigated in parallel without mechanical scanning, is described. 3rd Generation XDi is being driven among other things by technological developments taking place in the field of Multi-Focus X-ray Sources (MFXS) from which representative results are presented. MFXS source requirements for Next-Generation MIFB XDi are summarized and the potential of 3rd Generation XDi for rapid, accurate and affordable screening in the Checkpoint and Hold Baggage environments is summarized.
SALOME (an acronym for Small Angle Lab Operation Measuring Equipment) is a versatile, energy-dispersive x-ray diffraction imaging (XDi) test-bed facility; commissioned, funded and supported by the Transportation Security Laboratory, Atlantic City, USA. In work presented here, SALOME has been used to investigate the photon collection efficiency of three beam topologies that have been proposed for Next-Generation XDi, namely: Direct Fan-beam (DFB); Parallel Beam (PB); and Inverse Fan-beam (IFB).The single channel replication unit for each of the three topologies was implemented on SALOME. The apertures defining each topology were varied in width, influencing both the detector scatter signal and the momentum resolution. A small powder graphite sample was used as reference object for these measurements, as it provided simultaneous data on counting rate as well as peak resolution for the selected Bragg peak. The photon collection efficiencies at constant momentum peak width for the DFB, PB and IFB topologies were found to follow the trend (from lowest to highest, respectively) conjectured elsewhere in the scientific literature.The basic structure of SALOME is illustrated in Figure 1. The x-ray source is a commercially-available rotating anode electron impact x-ray source operable up to 160 kV and 12 kW DC. The source is supported on a demountable table that is accurately aligned relative to the apertures defining the primary and scatter x-ray beams; thus enabling the radiation source to be exchanged without affecting system alignment. The two primary beam apertures P1 and P2 define a primary beam propagating in the XY plane. The object to be analyzed is mounted on a table whose position in the YZ plane can be moved under computer control. The secondary collimators and spectroscopic detector are mounted on a cantilever table whose angle relative to the primary beam plane can be varied from 0° to 10°. The secondary collimators S1 and S2 define a scatter beam that intersects the primary beam in the sensitive region of the device, where the scatter voxel is located. The fulcrum of the cantilever table is designed to intersect the object table at the scatter voxel so that a change in angle of scatter does not affect the location of the material under investigation. A variety of spectroscopic detectors, including cryostatically cooled germanium as well as room temperature semiconductors such as CdTe and CdZnTe can be mounted on the cantilever table for the purpose of recording energy-dispersive XRD profiles. SALOME was designed to enable spatially resolved, energy-dispersive XRD profiles to be acquired under controlled, variable conditions including: angle of scatter, θ; x-ray source accelerating potential; dimensions of apertures defining the primary and scatter beams; attenuation characteristics; and multiple scatter degradation. In order to minimize the time taken for data acquisition a measurement topology was sought that maximized the photon throughput. As will be seen below, the photon throughput can be increased by t...
A description is given of the principle of operation, design and technical realization of a Compton spectrometer. In contrast to many other devices that have been discussed in the literature, the Compton spectrometer described here combines an electron-impact x-ray source with a room-temperature semiconductor detector.It is shown that the momentum resolution of the Compton spectrometer for the K characteristic lines emitted by the tube anode is adequate to resolve the Doppler broadening originating in electron momentum distributions of low atomic number elements, such as carbon, nitrogen and oxygen. Experimental Compton-broadened spectra from a range of common materials are presented. Methods to extract Compton profiles from the experimental spectra, by accounting for the continuous component of the x-ray tube emission and the multiplet nature of the characteristic lines, are illustrated. The application of this Compton spectrometer to material characterization is briefly discussed.
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