Determination of Radiation Damage Ages on Parts of Zircon Grains by Raman Microprobe: Implications for Annealing History and U-Pb Stability

1998 ◽  
Vol 62A (2) ◽  
pp. 1174-1175 ◽  
Author(s):  
R. T. Pidgeon
Keyword(s):  
Radiation Damage ◽  
Raman Microprobe

A Raman microprobe study of natural micas

1989 ◽  
Vol 53 (370) ◽  
pp. 165-179 ◽  
Author(s):  
A. Tlili ◽  
D. C. Smith ◽  
J.-M. Beny ◽  
H. Boyer
Keyword(s):  
Chemical Analysis ◽  
Polarization Direction ◽  
Chemical Parameters ◽  
Raman Spectrometry ◽  
Data Set ◽  
Octahedral Sites ◽  
Wide Range ◽  
Raman Microprobe ◽  
Ionic Size

AbstractA wide range of natural K-, Na-, Ca- or (K + Li)-micas have been systematically examined by Raman spectrometry. The spectra are interpretable in terms of regular variations in peak positions and chemical parameters. Several vibrations give higher wavenumbers for Na-micas compared to K-micas, in accord with the smaller ionic size of Na+ than K+. The ≈195 cm-1 and ≈270 cm-1 peak wavenumbers and intensities vary as functions of the chemistry of the octahedral sites, i.e. the replacement of Mg2+ by Mn2+, Zn2+, Cr3+, Fe3+, Ti4+, and especially by Al3+, or by a vacancy, and the replacement of (OH)- by F-. The group of ≈700 cm-1 peaks vary in wavenumber and intensity with the replacement of Si by Al in the tetrahedra; distinct Si-O-Si and Si-O-Al vibrations can be recognized. Di- and tri-octahedral micas are distinguished on the basis of certain relative peak intensities which vary considerably with polarization direction, and of trends with increasing Al(iv), Al(vi) or Al(tot.). Calibration of these trends for the chemical analysis of mica microinclusions seems feasible once the uncertainties in the data set are resolved by the determination of further samples selected to highlight the effect of specific elements.

scholarly journals Native sulfur/chlorine SAD phasing for serial femtosecond crystallography

2015 ◽  
Vol 71 (12) ◽  
pp. 2519-2525 ◽  
Author(s):  
Takanori Nakane ◽  
Changyong Song ◽  
Mamoru Suzuki ◽  
Eriko Nango ◽  
Jun Kobayashi ◽  
...  
Keyword(s):  
Radiation Damage ◽  
Crystal Structures ◽  
Structure Determination ◽  
Anomalous Diffraction ◽  
Native Sulfur ◽  
Wide Range ◽  
Sad Phasing ◽  
Anomalous Signal ◽  
Serial Femtosecond Crystallography

Serial femtosecond crystallography (SFX) allows structures to be determined with minimal radiation damage. However, phasing native crystals in SFX is not very common. Here, the structure determination of native lysozyme from single-wavelength anomalous diffraction (SAD) by utilizing the anomalous signal of sulfur and chlorine at a wavelength of 1.77 Å is successfully demonstrated. This sulfur SAD method can be applied to a wide range of proteins, which will improve the determination of native crystal structures.

scholarly journals The Influence of Photoelectron Escape in Radiation Damage Simulations of Protein Micro-Crystallography

Crystals ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 267 ◽  
Author(s):  
Hugh Marman ◽  
Connie Darmanin ◽  
Brian Abbey
Keyword(s):  
Radiation Damage ◽  
Global Radiation ◽  
Protein Structures ◽  
Mean Free Path ◽  
High Energy ◽  
Spatially Resolved ◽  
Inelastic Mean Free Path ◽  
The Impact ◽  
Intensity Loss

Radiation damage represents a fundamental limit in the determination of protein structures via macromolecular crystallography (MX) at third-generation synchrotron sources. Over the past decade, improvements in both source and detector technology have led to MX experiments being performed with smaller and smaller crystals (on the order of a few microns), often using microfocus beams. Under these conditions, photoelectrons (PEs), the primary agents of radiation-damage in MX, may escape the diffraction volume prior to depositing all of their energy. The impact of PE escape is more significant at higher beam energies (>20 keV) as the electron inelastic mean free path (IMFP) is longer, allowing the electrons to deposit their energy over a larger area, extending further from their point of origin. Software such as RADDOSE-3D has been used extensively to predict the dose (energy absorbed per unit mass) that a crystal will absorb under a given set of experimental parameters and is an important component in planning a successful MX experiment. At the time this study was undertaken, dose predictions made using RADDOSE-3D were spatially-resolved, but did not yet account for the propagation of PEs through the diffraction volume. Hence, in the case of microfocus crystallography, it is anticipated that deviations may occur between the predicted and actual dose absorbed due to the influence of PEs. To explore this effect, we conducted a series of simulations of the dose absorbed by micron-sized crystals during microfocus MX experiments. Our simulations spanned beam and crystal sizes ranging from 1μm to 5μm for beam energies between 9 keV and 30 keV. Our simulations were spatially and temporarily resolved and accounted for the escape of PEs from the diffraction volume. The spatially-resolved dose maps produced by these simulations were used to predict the rate of intensity loss in a Bragg spot, a key metric for tracking global radiation damage. Our results were compared to predictions obtained using a recent version of RADDOSE-3D that did not account for PE escape; the predicted crystal lifetimes are shown to differ significantly for the smallest crystals and for high-energy beams, when PE escape is included in the simulations.

The potential and limitations of neutrons, electrons and X-rays for atomic resolution microscopy of unstained biological molecules

1995 ◽  
Vol 28 (2) ◽  
pp. 171-193 ◽  
Author(s):  
Richard Henderson
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Radiation Damage ◽  
Single Molecule ◽  
Biological Molecules ◽  
Atomic Resolution ◽  
Fast Neutrons ◽  
X Rays ◽  
Number Of Particles

SummaryRadiation damage is the main problem which prevents the determination of the structure of a single biological macromolecule at atomic resolution using any kind of microscopy. This is true whether neutrons, electrons or X-rays are used as the illumination. Forneutrons, the cross-section for nuclear capture and the associatedenergy deposition and radiation damage could be reduced by using samples that are fully deuterated and15N-labelled and by using fast neutrons, but single molecule biological microscopy is still not feasible. For naturally occurring biological material,electronsat present provide the most information for a given amount of radiation damage. Using phase contrast electron microscopy on biological molecules and macromolecular assemblies of ˜ 105molecular weight and above, there is in theory enough information present in the image to allow determination of the position and orientation of individual particles: the application of averaging methods can then be used to provide an atomic resolution structure. The images of approximately 10000 particles are required. Below 105molecular weight, some kind of crystal or other geometrically ordered aggregate is necessary to provide a sufficiently high combined molecular weight to allow for the alignment. In practice, the present quality of the best images still falls short of that attainable in theory and this means that a greater number of particles must be averaged and that the molecular weight limitation is somewhat larger than the predicted limit. ForX-rays, the amount of damage per useful elastic scattering event is several hundred times greater than for electrons at all wavelengths and energies and therefore the requirements on specimen size and number of particles are correspondingly larger. Because of the lack of sufficiently bright neutron sources in the foreseeable future, electron microscopy in practice provides the greatest potential for immediate progress.

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