The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
R F Egerton - One of the best experts on this subject based on the ideXlab platform.
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Radiation Damage to organic and inorganic specimens in the tem
Micron, 2019Co-Authors: R F EgertonAbstract:Symptoms of Radiation Damage are reviewed, followed by a brief description of the three main Damage mechanisms: knock-on displacement (predominant in electrically conducting specimens), ionization Damage (radiolysis), and electrostatic charging effects in poorly conducting specimens. Measurements of characteristic dose and Damage cross section are considered, together with direct and inverse dose-rate effects. Dose limited resolution is defined in terms of a characteristic dose and instrumental parameters. Damage control is discussed in terms of low-dose technique, choice of imaging mode, specimen temperature, specimen environment and TEM accelerating voltage. We examine the possibility of performing electron cryomicroscopy in STEM mode, with a judicious choice of probe current and probe diameter.
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control of Radiation Damage in the tem
Ultramicroscopy, 2013Co-Authors: R F EgertonAbstract:The problem of electron-beam Damage in the transmission electron microscope is reviewed, with an emphasis on radiolysis processes in soft materials and organic specimens. Factors that determine the dose-limited resolution are identified for three different operational modes: bright-field scattering-contrast, phase-contrast and dark-field microscopy. Methods of reducing Radiation Damage are discussed, including low-dose techniques, cooling or encapsulating the specimen, and the choice of imaging mode, incident-beam diameter and incident-electron energy. Further experiments are suggested as a means of obtaining a better understanding and control of electron-beam Damage.
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Radiation Damage in the tem and sem
Micron, 2004Co-Authors: R F Egerton, Marek MalacAbstract:We review the various ways in which an electron beam can adversely affect an organic or inorganic sample during examination in an electron microscope. The effects considered are: heating, electrostatic charging, ionization Damage (radiolysis), displacement Damage, sputtering and hydrocarbon contamination. In each case, strategies to minimise the Damage are identified. In the light of recent experimental evidence, we re-examine two common assumptions: that the amount of Radiation Damage is proportional to the electron dose and is independent of beam diameter; and that the extent of the Damage is proportional to the amount of energy deposited in the specimen.
David J Flannigan - One of the best experts on this subject based on the ideXlab platform.
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reducing Radiation Damage in soft matter with femtosecond timed single electron packets
Nano Letters, 2019Co-Authors: Elisah J Vandenbussche, David J FlanniganAbstract:Despite the development of a myriad of mitigation methods, Radiation Damage continues to be a major limiting factor in transmission electron microscopy. Intriguing results have been reported using ...
Robert L Shoeman - One of the best experts on this subject based on the ideXlab platform.
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Radiation Damage in protein serial femtosecond crystallography using an x ray free electron laser
Physical Review B, 2011Co-Authors: Lukas Lomb, T R M Barends, Stephan Kassemeyer, Andrew Aquila, L Foucar, Robert Hartmann, Benedikt Rudek, Daniel Rolles, A Rudenko, Robert L ShoemanAbstract:X-ray free-electron lasers deliver intense femtosecond pulses that promise to yield high resolution diffraction data of nanocrystals before the destruction of the sample by Radiation Damage. Diffraction intensities of lysozyme nanocrystals collected at the Linac Coherent Light Source using 2 keV photons were used for structure determination by molecular replacement and analyzed for Radiation Damage as a function of pulse length and fluence. Signatures of Radiation Damage are observed for pulses as short as 70 fs. Parametric scaling used in conventional crystallography does not account for the observed effects.
Elspeth F Garman - One of the best experts on this subject based on the ideXlab platform.
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Radiation Damage in macromolecular crystallography what is it and why should we care
Acta Crystallographica Section D-biological Crystallography, 2010Co-Authors: Elspeth F GarmanAbstract:Radiation Damage inflicted during diffraction data collection in macromolecular crystallography has re-emerged in the last decade as a major experimental and computational challenge, as even for crystals held at 100 K it can result in severe data-quality degradation and the appearance in solved structures of artefacts which affect biological interpretations. Here, the observable symptoms and basic physical processes involved in Radiation Damage are described and the concept of absorbed dose as the basic metric against which to monitor the experimentally observed changes is outlined. Investigations into Radiation Damage in macromolecular crystallography are ongoing and the number of studies is rapidly increasing. The current literature on the subject is compiled as a resource for the interested researcher.
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Radiation Damage in macromolecular cryocrystallography
Current Opinion in Structural Biology, 2006Co-Authors: Raimond B. G. Ravelli, Elspeth F GarmanAbstract:X-ray Radiation Damage to cryocooled (∼100 K) macromolecular crystals has emerged as a general problem, especially since the advent of third generation synchrotron undulator sources. Interest in understanding the physical and chemical phenomena behind the observed effects is growing rapidly. The specific structural Damage seen in electron density maps has to be accounted for when studying intermediates, and can sometimes be related to biological function. Radiation Damage induces non-isomorphism, thus hampering traditional phasing methods. However, specific Damage can also be used to obtain phases. With an increased knowledge of expected crystal lifetime, beamline characteristics and types of Damage, macromolecular crystallographers might soon be able to account for Radiation Damage in data collection, processing and phasing.
Venugopalan Nagarajan - One of the best experts on this subject based on the ideXlab platform.
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Radiation Damage in protein crystals is reduced with a micron sized x ray beam
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Ruslan Sanishvili, Derek W Yoder, Sudhir Babu Pothineni, Gerd Rosenbaum, Stefan Vogt, Sergey Stepanov, O Makarov, Stephen Corcoran, R Benn, Venugopalan NagarajanAbstract:Radiation Damage is a major limitation in crystallography of biological macromolecules, even for cryocooled samples, and is particularly acute in microdiffraction. For the X-ray energies most commonly used for protein crystallography at synchrotron sources, photoelectrons are the predominant source of Radiation Damage. If the beam size is small relative to the photoelectron path length, then the photoelectron may escape the beam footprint, resulting in less Damage in the illuminated volume. Thus, it may be possible to exploit this phenomenon to reduce Radiation-induced Damage during data measurement for techniques such as diffraction, spectroscopy, and imaging that use X-rays to probe both crystalline and noncrystalline biological samples. In a systematic and direct experimental demonstration of reduced Radiation Damage in protein crystals with small beams, Damage was measured as a function of micron-sized X-ray beams of decreasing dimensions. The Damage rate normalized for dose was reduced by a factor of three from the largest (15.6 μm) to the smallest (0.84 μm) X-ray beam used. Radiation-induced Damage to protein crystals was also mapped parallel and perpendicular to the polarization direction of an incident 1-μm X-ray beam. Damage was greatest at the beam center and decreased monotonically to zero at a distance of about 4 μm, establishing the range of photoelectrons. The observed Damage is less anisotropic than photoelectron emission probability, consistent with photoelectron trajectory simulations. These experimental results provide the basis for data collection protocols to mitigate with micron-sized X-ray beams the effects of Radiation Damage.
