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.

Determination of Mean Free Path for Inelastic Scattering in Poly(2-Vinyl Pyridine) by Low-Loss Spectrum Imaging

2000 ◽  
Vol 6 (S2) ◽  
pp. 224-225
Author(s):  
A. Aitouchen ◽  
T. Chou ◽  
M. Libera ◽  
M. Misra
Keyword(s):  
Free Path ◽  
Free Fall ◽  
Mean Free Path ◽  
Specimen Thickness ◽  
Thickness Determination ◽  
Vinyl Pyridine ◽  
Integrated Intensity ◽  
Inelastic Mean Free Path ◽  
Electron Energy Loss

The common experimental method to determine the total inelastic mean free path i by electron energy-loss spectroscopy (EELS) is by the relation : t/λi= ln(It/IO) [1] where t is the specimen thickness, It, is the total integrated intensity, and Io is the intensity of the zero-loss peak. The accuracy of this measurement depends on the thickness determination. Model geometries like cubes, wedges, and spheres enable accurate thickness determination from transmission images.Spherical polymers with diameters of order 10-200nm can be made from a number of high-Tg polymers by solvent atomization. This research studied atomized spheres of poly(2-vinyl pyridine) [PVP]. A solution of 0.1% PVP in THF was nebulized. After solvent evaporation during free fall within the chamber atmosphere, solid spherical polymer particles with a range of diameters were collected on holey-carbon TEM grids at the bottom of the atomization chamber.

scholarly journals Determination of Inelastic Mean Free Path of Electrons in Noble Metals

1992 ◽  
Vol 81 (2) ◽  
pp. 193-199 ◽  
Author(s):  
W. Doliński ◽  
S. Mróz ◽  
J. Palczyński ◽  
B. Gruzza ◽  
P. Bondot ◽  
...  
Keyword(s):  
Free Path ◽  
Noble Metals ◽  
Mean Free Path ◽  
Inelastic Mean Free Path

scholarly journals Constraining the stellar energetic particle flux in young solar-like stars

2018 ◽  
Vol 14 (S345) ◽  
pp. 310-311
Author(s):  
Ch. Rab ◽  
M. Padovani ◽  
M. Güdel ◽  
I. Kamp ◽  
W-F. Thi ◽  
...  
Keyword(s):  
Particle Flux ◽  
High Energy ◽  
Young Stars ◽  
Solar Cosmic Rays ◽  
Spatially Resolved ◽  
T Tauri ◽  
Ionization Sources ◽  
Hydrogen Ionization ◽  
The Individual ◽  
The Impact

AbstractAnomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a large number of energetic particles (E≳ 10 MeV), often called solar cosmic rays. The particle flux of the contemporary Sun cannot explain these anomalies, but, similar to T Tauri stars, the young Sun was more active and probably produced enough high energy particles. However, the stellar particle (SP) flux of young stars is essentially unknown. We model the impact of high-energy ionization sources on the chemistry of the circumstellar environment (disks and envelopes). The model includes X-ray radiative transfer and makes use of particle transport models to calculate the individual molecular hydrogen ionization rates. We study the impact on the chemistry via the ionization tracers HCO+ and N2H+. We argue that spatially resolved observations of those molecules combined with detailed models allow for disentangling the contribution of the individual high-energy ionization sources and to put constraints on the SP flux in young stars.

Refractory Metal Facings for Protection of Metal Surfaces Subjected to Repeated High-Temperature Pulses

1959 ◽  
Vol 81 (2) ◽  
pp. 197-202
Author(s):  
Aaron Cohen ◽  
Edward Homer
Keyword(s):  
Refractory Metal ◽  
Peak Power ◽  
Direct Relationship ◽  
High Energy ◽  
Analytical Determination ◽  
High Peak Power ◽  
Resonant Structure ◽  
High Energy Electrons ◽  
The Impact

Because the operating frequency of a magnetron has a direct relationship to the size of the resonant structure, the power at a given frequency that can be obtained from a magnetron may be limited by the temperature which the resonating structure can withstand. A rise in the temperature of the resonant structure is caused by the impact of high-energy electrons emitted from the cathode at high peak-power levels for short durations. This paper deals with the analytical determination of the temperature of the resonant structure, a solution to the heat problem in which a thin coating of refractory metal is used to prevent the vulnerable components from melting, and some experimental results to verify the analysis.

Determination of the Inelastic Mean-Free-Path and Mean Inner Potential for AlAs and GaAs Using Off-Axis Electron Holography and Convergent Beam Electron Diffraction

2007 ◽  
Vol 13 (5) ◽  
pp. 329-335 ◽  
Author(s):  
Suk Chung ◽  
David J. Smith ◽  
Martha R. McCartney
Keyword(s):  
Electron Diffraction ◽  
Theoretical Calculations ◽  
Mean Free Path ◽  
High Energy ◽  
Convergent Beam Electron Diffraction ◽  
Electron Holography ◽  
Beam Electron ◽  
The Mean ◽  
Convergent Beam ◽  
Inelastic Mean Free Path

The mean-free-paths for inelastic scattering of high-energy electrons (200 keV) for AlAs and GaAs have been determined based on a comparison of thicknesses as measured by electron holography and convergent-beam electron diffraction. The measured values are 77 ± 4 nm and 67 ± 4 nm for AlAs and GaAs, respectively. Using these values, the mean inner potentials of AlAs and GaAs were then determined, from a total of 15 separate experimental measurements, to be 12.1 ± 0.7 V and 14.0 ± 0.6 V, respectively. These latter measurements show good agreement with recent theoretical calculations within experimental error.

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