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26 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B16-Test Beamline	Alanine response to low energy synchrotron x-ray radiation Peregrin Van Den Elzen , Thorsten Sander , Hugo Palmans , Michael Mcmanus , Nathaniel Woodall , Nigel Lee , Oliver J. L. Fox , Roger Michael Jones , Deepa Angal-Kalinin , Anna Subiel Physics In Medicine & Biology DOI: 10.1088/1361-6560/acb886 Open Access Show Abstract ▼ Abstract: Alanine pellets with a nominal thickness of 0.5 mm and diameter of 5 mm were irradiated with monoenergetic x-rays at the Diamond Light Source synchrotron, to quantify their response in the 8 to 20 keV range relative to 60Co radiation. The absorbed dose to graphite was measured with a small portable graphite calorimeter, and the DOSRZnrc code in the EGSnrc Monte Carlo package was used to calculate conversion factors between the measured dose to graphite and the absorbed dose to water delivered to the alanine pellets. GafChromic EBT3 films were used to measure the beam profile for modelling in the MC simulations. The relative responses measured in this energy range were found to range from 0.616 to 0.643, with a combined relative expanded uncertainty of 3.4% to 3.5% (k = 2), where the majority of the uncertainty originated from the uncertainty in the alanine readout, due to the small size of the pellets used. The measured values were in good agreement with previously published data in the overlapping region of x-ray energies, while this work extended the dataset to lower energies. By measuring the response to monoenergetic x-rays, the response to a more complex broad-spectrum x-ray source can be inferred if the spectrum is known, meaning that this work supports the establishment of alanine as a secondary standard dosimeter for low-energy x-ray sources.	Feb 2023
B16-Test Beamline Metrology Optics	Two-dimensional speckle technique for slope error measurements of weakly focusing reflective X-ray optics Lingfei Hu , Hongchang Wang , Oliver Fox , Kawal Sawhney Journal Of Synchrotron Radiation 29 DOI: 10.1107/S160057752200916X Open Access Show Abstract ▼ Abstract: Speckle-based at-wavelength metrology techniques now play an important role in X-ray wavefront measurements. However, for reflective X-ray optics, the majority of existing speckle-based methods fail to provide reliable 2D information about the optical surface being characterized. Compared with the 1D information typically output from speckled-based methods, a 2D map is more informative for understanding the overall quality of the optic being tested. In this paper, we propose a method for in situ 2D absolute metrology of weakly focusing X-ray mirrors. Importantly, the angular misalignment of the mirror can be easily corrected with the proposed 2D processing procedure. We hope the speckle pattern data processing method presented here will help to extend this technique to wider applications in the synchrotron radiation and X-ray free-electron laser communities.	Nov 2022
B16-Test Beamline Optics	Fast wavefront sensing for X-ray optics with an alternating speckle tracking technique Lingfei Hu , Hongchang Wang , Oliver Fox , Kawal Sawhney Optics Express 30 DOI: 10.1364/OE.460163 Open Access Show Abstract ▼ Abstract: Advances in accelerator technologies have enabled the continuous development of synchrotron radiation and X-ray free electron laser (XFEL) sources. At the same time, it has been critical to perform in-situ wavefront sensing to aid delivery of high-quality X-ray beams to the end users of these facilities. The speckle-based scanning technique has obtained popularity due to its high spatial resolution and superior sensitivity compared to other wavefront sensing methods. However, these advantages often come at the expense of longer data acquisition times since multiple images have to be collected to derive the necessary wavefront information. Whereas initial speckle tracking techniques could obtain wavefront information relatively quickly, the installation of additional hardware was routinely required to do so. Here, we propose a novel speckle-based approach, termed Alternating Speckle Tracking (AST), to perform fast wavefront sensing within a conventional beamline setup. The wavefront information derived from the new technique has proven to be valuable for many applications that require temporal resolution. Importantly, both horizontal and vertical wavefront information can be simultaneously derived by moving the speckle generator along the diagonal direction. We expect this method will be widely used by the synchrotron radiation and XFEL community in the future.	Aug 2022
B16-Test Beamline Optics	Two-dimensional wavefront characterization of adaptable corrective optics and Kirkpatrick–Baez mirror system using ptychography Thomas E. J. Moxham , Vishal Dhamgaye , David Laundy , Oliver J. L. Fox , Hossein Khosroabadi , Kawal Sawhney , Alexander Korsunsky Optics Express 30 DOI: 10.1364/OE.453239 Open Access Show Abstract ▼ Abstract: Aberrations introduced during fabrication degrade the performance of X-ray optics and their ability to achieve diffraction limited focusing. Corrective optics can counteract these errors by introducing wavefront perturbations prior to the optic which cancel out the distortions. Here we demonstrate two-dimensional wavefront correction of an aberrated Kirkpatrick-Baez mirror pair using adaptable refractive structures. The resulting two-dimensional wavefront is measured using hard X-ray ptychography to recover the complex probe wavefield with high spatial resolution and model the optical performance under coherent conditions. The optical performance including the beam caustic, focal profile and wavefront error is examined before and after correction with both mirrors found to be diffraction limited after correcting. The results will be applicable to a wide variety of high numerical aperture X-ray optics aiming to achieve diffraction limited focussing using low emittance sources.	May 2022
Optics	Refractive optics for modifying X-ray wavefronts David Laundy , Thomas Moxham , Vishal Dhamgaye , Hossein Khosroabadi , Oliver Fox , Kawal Sawhney Synchrotron Radiation News DOI: 10.1080/08940886.2021.2022400 Open Access	Feb 2022
B16-Test Beamline I15-Extreme Conditions	First observation of radiolytic bubble formation in unstirred nano-powder sludges and a consistent model thereof Mel O'Leary , Aliaksandr Baidak , Martyn Barnes , Thomas Donoclift , Christopher Emerson , Catarina Figueira , Oliver Fox , Annette Kleppe , Aaron Mcculloch , Darryl Messer , Robin Orr , Fred Currell Scientific Reports 11 DOI: 10.1038/s41598-021-01868-1 Diamond Proposal Number(s): [21977, 20531, 20469, 19017, 17524, 17519, 16218] Open Access Show Abstract ▼ Abstract: Experiments involving the irradiation of water contained within magnesium hydroxide and alumina nanoparticle sludges were conducted and culminated in observations of an increased yield of molecular hydrogen when compared to the yield from the irradiation of bulk water. We show that there is a relationship linking this increased yield to the direct nanoscale ionization mechanism in the nanoparticles, indicating that electron emission from the nanoparticles drives new radiative pathways in the water. Because the chemical changes in these sludges are introduced by irradiation only, we have a genuinely unstirred system. This feature allows us to determine the diffusivity of the dissolved gas. Using the measured gas production rate, we have developed a method for modelling when hydrogen bubble formation will occur within the nanoparticle sludges. This model facilitates the determination of a consistent radiolytic consumption rate coinciding with the observations of bubble formation. Thus, we demonstrate a nanoscale radiation effect directly influencing the formation of molecular hydrogen.	Nov 2021
B16-Test Beamline Detectors Optics	Improved spatial resolution in X-ray microscopy using a tilted angle detector Polad Shikhaliev , Oliver Fox , Nicola Tartoni 2020 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) DOI: 10.1109/NSS/MIC42677.2020.9507906 Show Abstract ▼ Abstract: We performed simulations and experimental tests of a new method for improving the spatial resolution of x-ray imaging detectors using tilted angle irradiation. In this method, the x-ray beam arrives at the detector surface at an angle of <90° so that the beam footprint is expanded and the spatial resolution is increased. The proposed method is applicable for imaging with x-rays in the energy range of E = 0.2-15 keV, which is widely used for x-ray microscopy. The tilted angle irradiation technique can be applied to different types of x-ray microscopy detectors, including indirect conversion detectors (which consist of a scintillator optically coupled to the imaging camera), direct conversion detectors (such as CCD- and CMOS-based soft x-ray cameras) and some other semiconductor detectors. The experimental study described here employed an indirect detector configuration where a thin scintillator was optically coupled to an imaging camera via microscope optics. The spatial resolution was improved by a factor of 2.5 by using a tilt angle of 12° for 13.5 keV x-rays. This study will be continued using different xray energies and detector configurations.	Aug 2021
B16-Test Beamline	X-ray microbeam characterisation of crystalline defects in small pixel GaAs:Cr detectors R. M. Wheater , L. Jowitt , S. Richards , M. C. Veale , M. D. Wilson , O. J. L. Fox , K. J. S. Sawhney , A. D. Lozinskaya , A. Shemeryankina , O. P. Tolbanov , A. Tyazhev , A. N. Zarubin Nuclear Instruments And Methods In Physics Research Section A: Accelerators, Spectrometers, Detectors And Associated Equipment DOI: 10.1016/j.nima.2021.165207 Diamond Proposal Number(s): [23500] Show Abstract ▼ Abstract: A newly supplied 80 × 80 chromium compensated GaAs sensor with a matrix of 80 × 80 pixels on a 250 m pixel pitch has been characterised utilising microbeam mapping techniques at the Diamond Light Source. The GaAs:Cr sensor was mounted to a HEXITEC DAQ system before raster scanning an x-ray beam with area 25 × 25 m in steps of 25 m, providing sub-pixel resolution spectroscopic imaging. Scans were performed with incident x-ray energies ranging from 12 to 45 keV. Following processing of the data in MatLab 2019b an analysis of defects previously observed in etched GaAs wafers occured. Findings indicate the presence of regions with reduced charge collection efficiency where up to 88 % of incident events show significant charge loss, and changing charge carrier lifetimes across the sensor.	Mar 2021
B16-Test Beamline Optics	Aberration characterization of x-ray optics using multi-modal ptychography and a partially coherent source Thomas E. J. Moxham , David Laundy , Vishal Dhamgaye , Oliver J. L. Fox , Kawal Sawhney , Alexander M. Korsunsky Applied Physics Letters 118 DOI: 10.1063/5.0041341 Show Abstract ▼ Abstract: Ptychography is a scanning coherent diffraction imaging technique that provides high-resolution imaging and complete spatial information of the complex probe and object transmission function. The wavefront error caused by aberrated optics has previously been recovered using ptychography when a highly coherent source is used, but has not been demonstrated with partial coherence due to the multi-modal probe required. Here, we demonstrate that partial coherence can be accounted for in ptychographic reconstructions using the multi-modal approach and assuming that decoherence arises from either the probe or the object. This equivalence recovers coherent (or single state) reconstructions of both the probe and the object even in the presence of partial coherence. We demonstrate this experimentally by using hard x-ray ptychography with a partially coherent source to image a Siemens star test object and to also recover the wavefront error from an aberrated beryllium compound refractive lens. The source properties and resolving capabilities are analyzed, and the wavefront error results are compared with another at-wavelength metrology technique. Our work demonstrates the capability of ptychography to provide high-resolution imaging and optics characterization even in the presence of partial coherence.	Mar 2021
B16-Test Beamline	Characterisation of Ge micro-strip sensors with a micro-focused X-ray beam M. Borri , C. Cohen , O. Fox , J. Groves , W. Helsby , O. Mathon , L. Mcnicholl , S. Pascarelli , K. Sawhney , R. Torchio , M. Zuvic Nuclear Instruments And Methods In Physics Research Section A: Accelerators, Spectrometers, Detectors And Associated Equipment DOI: 10.1016/j.nima.2020.164932 Diamond Proposal Number(s): [24637] Open Access Show Abstract ▼ Abstract: Germanium micro-strip sensors were selected as the sensor technology to take data in energy dispersive X-ray spectroscopy experiments at the Extremely Brilliant Source (EBS) in Grenoble (FR). It is important for this experimental technique to use sensors with a large uniform area and a fine pitch. The former determines the range of energy detectable with a single sensor. The latter improves spectral resolution. A high stopping power is also important to perform studies with hard X-rays. The device under test in this measurement was a germanium micro-strip sensor made of 1024 strips with pitch. The bulk was 1.5 mm thick. The sensor was assembled into a prototype cryostat part of the XH detector system. The device was tested at the B16 beamline at the Diamond Light Source (DLS) in Didcot (UK). The objective of the test-beam was to characterise charge-sharing between strips. In fact, this effect limits the spectral resolution of the device. To carry out this test, the sensor was scanned over a subset of strips with micro-focused X-rays under different settings. These were beam energy and intensity, sensor temperature and bias voltage. Results are presented in this paper. It was measured that the full width half maximum of the charge-sharing profile across different strips was for settings which were indicative of the experimental conditions at the EBS. This was a signal current per unit area on the sensor of 10−8 A/ , a bias voltage of -180 V and a temperature of -159 C.	Dec 2020

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