Browsing by Author "Evans, Paul"

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    Age-related changes in femoral head trabecular microarchitecture
    (Buck Institute for Age Research, 2017-10-11) Greenwood, Charlene; Clement, John; Dicken, Anthony; Evans, Paul; Lyburn, Iain Douglas; Martin, Richard M.; Stone, Nick; Zioupos, Peter; Rogers, Keith
    Osteoporosis is a prevalent bone condition, characterised by low bone mineral density and increased fracture risk. Currently, the gold standard for identifying osteoporosis and increased fracture risk is through quantification of bone mineral density using dual energy X-ray absorption. However, many studies have shown that bone strength, and consequently the probability of fracture, is a combination of both bone mass and bone ‘quality’ (architecture and material chemistry). Although the microarchitecture of both non-fracture and osteoporotic bone has been previously investigated, many of the osteoporotic studies are constrained by factors such as limited sample number, use of ovariectomised animal models, and lack of male and female discrimination. This study reports significant differences in bone quality with respect to the microarchitecture between fractured and non-fractured human femur specimens. Micro-computed tomography was utilised to investigate the microarchitecture of femoral head trabecular bone from a relatively large cohort of non-fracture and fracture human donors. Various microarchitectural parameters have been determined for both groups, providing an understanding of the differences between fracture and non -fracture material. The microarchitecture of non-fracture and fracture bone tissue is shown to be significantly different for many parameters. Differences between sexes also exist, suggesting differences in remodelling between males and females in the fracture group. The results from this study will, in the future, be applied to develop a fracture model which encompasses bone density, architecture and material chemical properties for both female and male tissues.
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    Chapter 6: X-Ray diffraction and focal construct technology
    (CRC Press, 2018-11-02) Rogers, Keith; Evans, Paul
    This chapter examines the background and practice of X-ray diffraction (XRD) and considers this phenomenon principally in the context of X-ray-based security screening. The focus will be upon the practical aspects of XRD as many texts already provide comprehensive descriptions of the relevant theoretical background and that of the closely associated area of crystallography. X-ray diffraction and its development from simple materials identification to dynamic imaging will be considered, followed by a similar view of aviation screening. Subsequently, a new approach to the harvesting of diffraction signatures (Focal Construct Technology) will be introduced and consequent potential applications summarised.
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    Conical shell illumination incorporating a moving aperture for depth-resolved high-energy X-ray diffraction
    (Royal Society of Chemistry, 2023-01-16) Spence, Daniel; Dicken, Anthony; Downes, David; Rogers, Keith; Evans, Paul
    In many applications, the main limitation of X-ray absorption methods is that the signals measured are a function of the attenuation coefficient, which tells us almost nothing about the chemical or crystallographic nature of objects under inspection. To calculate fundamental crystallographic parameters requires the measurement of diffracted photons from a sample. Standard laboratory diffraction methods have been refined for well over a century and provide ‘gold standard’ structural models for well-prepared samples and single crystals but have little applicability for thick heterogeneous samples as demanded by many screening applications. We present a new high-energy X-ray diffraction probe, which in comparison with previous depth-resolving hollow beam techniques, requires a single beam, point detector and a simple swept aperture to resolve sample signatures at unknown locations within an inspection space. We perform Monte Carlo simulations to support experiments on both single- and multiple-material localisation and identification. The new probe is configured and tested using low-cost commercial components to provide a rapid and cost-effective solution for applications including explosives detection, process control and diagnostics.
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    Data supporting "A new parafocusing paradigm for X-ray diffraction"
    (Cranfield University, 2020-12-09 10:07) Prokopiou, Danae; McGovern, James; Davies, Gareth; Godber, Simon; Rogers, Keith; Evans, Paul; Dicken, Anthony
    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.
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    Dual conical shell illumination for volumetric high-energy x-ray diffraction imaging
    (Royal Society of Chemistry, 2018-09-13) Dicken, Anthony; Spence, Daniel; Rogers, Keith; Prokopiou, Danae; Evans, Paul
    To retrieve crystallographic information from extended sample volumes requires a high-energy probe. The use of X-rays to combine imaging with materials characterisation is well-established. However, if fundamental crystallographic parameters are required, then the collection and analysis of X-rays diffracted by the inspected samples are prerequisites. We present a new X-ray diffraction imaging architecture, which in comparison with previous depth-resolving hollow beam techniques requires significantly less X-ray power or alternatively supports significantly increased scanning speeds. Our conceptual configuration employs a pair of conical shell X-ray beams derived from a single point source to illuminate extended samples. Diffracted flux measurements would then be obtained using a pair of energy resolving point detectors. This dual beam configuration is tested using a single X-ray beam set-up employing a dual scan. The use of commercial off-the-shelf low-cost components has the potential to provide rapid and cost-effective performance in areas including industrial process control, medical imaging and explosives detection.
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    High energy transmission annular beam X-ray diffraction
    (Optical Society of America, 2015-02-02) Dicken, Anthony; Shevchuk, Alex; Rogers, Keith; Godber, Simon; Evans, Paul
    We demonstrate material phase retrieval by linearly translating extended polycrystalline samples along the symmetry axis of an annular beam of high-energy X-rays. A series of pseudo-monochromatic diffraction images are recorded from the dark region encompassed by the beam. We measure Bragg maxima from different annular gauge volumes in the form of bright spots in the X-ray diffraction intensity. We present the experiment data from three materials with different crystallographic structural properties i.e. near ideal, large grain size and preferred orientation. This technique shows great promise for analytical inspection tasks requiring highly penetrating radiation such as security screening, medicine and nondestructive testing.
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    A new parafocusing paradigm for X-ray diffraction
    (International Union of Crystallography, 2020-07-24) Prokopiou, Danae; McGovern, James; Davies, Gareth; Godber, Simon; Evans, Paul; Dicken, Anthony; Rogers, Keith
    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.
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    Position determination of scatter signatures – A novel sensor geometry
    (Elsevier, 2010-09-25) Dicken, Anthony; Rogers, Keith; Evans, Paul; Rogers, Joseph; Chan, Jer Wang; Xun, Wang
    A novel diffraction sensor geometry able to provide the diffraction pattern of a suspect material without prior knowledge of the samples location is introduced. The sensor geometry can also resolve diffraction patterns originating from multiple unknown materials overlapped along the primary X-ray beam path. This is achieved through tracking Bragg peak maxima that linearly propagate from the inspection volume at a series of X-ray detector positions. A series of simulations and experiments have been performed to verify this technique and provide an insight into its characteristics. Such a technique could have widespread appeal in the security industry. Areas of most relevance include the materials characterisation of volumes such as those prevalent in an airport screening environment or equally the rapid screening for illicit drugs trafficked through the postal system.
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    Simulations and experimental demonstrations of encoding for X-ray coherent scattering
    (International Union of Crystallography, 2017-04-01) Prokopiou, Danae; Smith, Kerrie L.; Rogers, Keith; Paula, P.; Evans, Paul; Dicken, Anthony; Godber, S.
    Diffraction data may be measured using approaches that lead to ambiguity in the interpretation of scattering distributions. Thus, the encoding and decoding of coherent scatter 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 a second regime, encoding of Debye cones is shown to enable recovery of sample position relative to the detector. The errors associated with both regimes are considered and the advantages of combining both discussed.
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    Thermally dynamic examination of local order in nanocrystalline hydroxyapatite
    (Elsevier, 2022-08-13) Arnold, Emily; Gosling, Sarah; Davies, Samantha K.; Cross, Hannah L.; Evans, Paul; Keeble, Dean S.; Greenwood, Charlene; Rogers, Keith D.
    The main mineral component of bone is hydroxyapatite, a commonly nanocrystalline material which presents many challenges for those trying to characterize it. Here, local structure is analyzed using X-ray total scattering for synthetic samples, to enable a better understanding of the nanocrystalline nature of hydroxyapatite. Two samples were measured dynamically during heat treatment from 25°C to 800°C, and were analyzed using small box modelling. Analysis of sequential measurements when dwelling at key temperatures showed a significant relationship between time and temperature, indicating a process occurring more slowly than thermal expansion. This indicates a decrease in B-type CO32- substitution between 550°C and 575°C and an increase in A-type CO32- substitution above 750°C. A greater understanding of local, intermediate, and long-range order of this complex biomineral during heat treatment can be of interest in several sectors, such as in forensic, biomedical and clinical settings for the study of implant coatings and bone diseases including osteoporosis and osteoarthritis.