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Catalytic Surfaces and Catalyst Characterization Methods
Published in James J. Carberry, Arvind Varma, Chemical Reaction and Reactor Engineering, 2020
W. Nicholas Delgass, Eduardo E. Wolf
The alternative approaches mentioned above may eventually provide routine access to EXAFS-type information. X-ray absorption measurements can be made with conventional x-ray sources (Knapp et al., 1978; del Cueto and Shevchik, 1977) but counting times are generally long compared to those obtained with the intense beams available from synchroton radiation (Hayes and Boyce, 1982). Since absorption must be scanned as a function of energy, a broad continuous band of radiation is needed and the sharp emission lines of the conventional x-ray source must be avoided. A synchrotron or storage ring produces this radiation by the curved orbit of a beam of high-energy electrons. This, or the Bremstrahlung background radiation of an x-ray tube, is passed through a monochromator and then through an incident flux detector, the sample, and a transmitted flux detector. X-ray energy is scanned with the monochromator. The raw data, transmitted intensity ratio as a function of energy, are then treated as described in the preceding section. As with any work on catalysts, proper cells for pretreating the sample and maintaining its environment during the measurement are essential (Via et al., 1979). Samples are often maintained at low temperatures (80 to 100 K) to decrease the mean-square displacement of the atoms and improve resolution.
Fundamentals
Published in Stuart R. Stock, MicroComputed Tomography, 2019
Several types of devices produce the intense magnetic fields required to produce synchrotron radiation (Fig. 2.3). Bending magnets situated periodically around the storage ring deflect the electrons and force them to circulate within the ring (which is a polygon and not a circle). Insertion devices placed between the bending magnets and consisting of a number of closely spaced magnets are another way synchrotron radiation is delivered to experiments. Each bending magnet or insertion device line at a given synchrotron is optimized for certain operating characteristics, and it is beyond the scope of this section to discuss specifics of x-ray imaging stations at a particular ring. Storage rings for synchrotron radiation are typically very large facilities and are found around the world. Because the characteristics of each differ so markedly and change from time to time, the interested reader is advised to do an internet search for further details. Recent development of tabletop synchrotron radiation sources offers another option for x-ray brightness imaging (Hirai, Yamada et al. 2006).
Fundamentals
Published in Stuart R. Stock, MicroComputed Tomography, 2018
Several types of devices produce the intense magnetic fields required to produce synchrotron radiation (Figure 2.3). Bending magnets situated periodically around the storage ring deflect the electrons and force them to circulate within the ring (which is a polygon and not a circle). Insertion devices placed between the bending magnets and consisting of a number of closely spaced magnets are another way synchrotron radiation is delivered to experiments. Each bending magnet or insertion device line at a given synchrotron is optimized for certain operating characteristics, and it is beyond the scope of this section to discuss specifics of x-ray imaging stations at a particular ring. Storage rings for synchrotron radiation are typically very large facilities and are found around the world. The characteristics of each differ markedly and change from time to time, the interested reader is advised to do an Internet search for further details. Recent development of tabletop synchrotron radiation sources offers another option for x-ray brightness imaging (Hirai et al., 2006).
Standard variable short period microwave-plasma undulator
Published in Waves in Random and Complex Media, 2023
Mansour Hadad, Sirous Yousefnejad, Farhad Saeidi, Javad Rahighi, Babak Shokri
The Lorentz force states that an electron beam undergoes oscillations and wiggles while moving through electromagnetic fields. The deflection parameter (K) of an undulator is defined as the maximum deflection angle of electron beam. This parameter governs the properties of synchrotron radiation such as energy, flux, and brilliance. To calculate the deflection parameter of an undulator, an electron beam with the initial movement along z-axis under the influence of the Lorentz force and its component along x-direction in the form of is considered. It should be mentioned that electron beam energy in the storage ring is assumed to be constant. Since the electron beam energy reduction due to synchrotron radiation generation is negligible, and a Linac in the storage ring compensates for electron beam energy reduction. So in a good approximation in Equation (15), .
A study of thickness dependent microstructure of poly (3-hexylthiophene) thin films using grazing incidence x-ray diffraction
Published in Soft Materials, 2022
Manoj Kumar, Srihari Velaga, Amarjeet Singh
Δβ is the vertical angular acceptance of the detector slit, I0 is incident beam intensity and t is thickness of the given film. N is the normalization constant so that the highest DOC is normalized to unity. Isig(q) and Ibkg(q) are diffraction signal and background signal. 1D-GID measurement is sensitive to only perfectly oriented (with angular resolution ~ 0.1°) crystallites parallel to the substrate (dark gray bars in Figure 3) so that lamellar stacking alkyl chains is along vertical direction. Integration of equation 1 corresponds to the area under a given peak from starting point of peak to the end point of the peak. At first diffraction signal was obtained using standard background correction procedure where wave vector dependence of background was fitted and subtracted from the original data as provided in supporting information. The diffraction intensity was normalized with film thickness for all 1D-GID measurements. Normalization with incident beam intensity is also required since it changes due to decay of storage current in the storage ring of synchrotron radiation. The normalization with incident intensity and film thickness is provided in supporting information. Factor Δβ in equation 1 has no effect on DOC as angular acceptance remains same for all samples.
Effect of size and surface chemistry of gold nanoparticles on their retention in a sediment-water system and Lumbriculus variegatus
Published in Journal of Environmental Science and Health, Part A, 2021
Ping Luo, Guibin Ma, Agnieszka Dudkiewicz, Zhen Mao, Lizhang Wang, Jiachao Jiang
Au mapping in L. variegatus exposed to different AuENPs for 14 days without depuration was performed at the ANKA synchrotron test facility, Karlsruhe Institute of Technology (KIT, Karlsruhe, Germany) using tomographic X-ray fluorescence (XRF). The synchrotron radiation (6.2 keV) was produced by a 2.5 GeV second-generation storage ring and accelerated in the magnetic field (1.5 T bending magnets) with 5.6 m radius curvature. After initial monitoring, low energy filtration and collimation, the primary emitted beam was split by a W/BC4 multilayer monochromator (3 nm layer period, 2.5–24.7 keV) to allow the capture of Au and Fe spectra.[31] Fe is an essential element of haemerythrin in L. variegatus plasma, which transforms from the ferrous (Fe2+) to the ferric state (Fe3+) to bind oxygen.[32] Therefore, Fe elemental mapping can be used to visualize the body shape of L. variegatus. The elemental maps of Au and Fe were then overlaid to visualize the locations at which Au was present.[33]