Comparison between the neutron central peak and the x-ray quasi-Bragg peak in pureKMnF3

1990 ◽  
Vol 42 (13) ◽  
pp. 8255-8260 ◽  
Author(s):  
A. Gibaud ◽  
H. You ◽  
S. M. Shapiro ◽  
J. Y. Gesland
Keyword(s):  
Bragg Peak ◽  
Central Peak ◽  
X Ray

scholarly journals Alternatives to the Existence of Large Cooling Flows

1990 ◽  
Vol 115 ◽  
pp. 232-239
Author(s):  
Wallace Tucker
Keyword(s):  
Surface Brightness ◽  
Large Scale ◽  
Theoretical Calculations ◽  
Central Peak ◽  
High Energy ◽  
Cooling Time ◽  
Radiative Cooling ◽  
Massive Black Hole ◽  
X Ray ◽  
Cooling Flows

AbstractArguments against the existence of large scale cooling flows in clusters of galaxies are presented. The evidence for cooling flows is all circumstantial, consisting of observations of cool gas or hot gas with a radiative cooling time less than the Hubble time, or a central peak in the x-ray surface brightness profile. There is no evidence for large quantities (several tens to several hundreds of solar masses per year) of matter actually flowing anywhere. On the contrary, several lines of evidence — stellar dynamics, observations of the amount of star formation, x-ray surface brightness observations, theoretical calculations of the growth of thermal instabilities, the amount of cold gas — suggest that cooling flows, if they exist, must be suppressed by one to two orders of magnitude from the values implied by simple estimates based on the radiative cooling time of the x-ray emitting gas. Two heat sources which might accomplish this — thermal conduction and relativistic particles, are considered and an alternative to the standard model for cooling flows is presented: an accretion flow with feedback wherein the accretion of gas into a massive black hole in the central galaxy generates high energy particles that heat the gas and act to limit the accretion.

High Resolution X-ray Diffraction for the Characterization of Semiconducting Materials

1989 ◽  
Vol 33 ◽  
pp. 1-11 ◽  
Author(s):  
B. K. Tanner
Keyword(s):  
Bragg Peak ◽  
Thin Layers ◽  
X Ray Diffraction ◽  
Semiconducting Materials ◽  
Multiple Reflections ◽  
X Ray ◽  
Analyzer Crystal ◽  
Glancing Angle ◽  
Heteroepitaxial Layers

AbstractUse of a reference crystal to condition the beam in the double-axis diffractometer permits the Bragg peak width to be reduced to the correlation of the two crystal reflecting ranges. Some recent applications of double axis diffractometry to the study of heteroepitaxial layers are discussed. The advantages of multiple reflections for beam conditioning and the four reflection DuMond monochromator are examined. Glancing incidence and exit diffractometry permits the study of very thin layers, down to a few tens of nanometres in thickness and both synchrotron radiation and skew reflections can be used to tune the glancing angle close to the critical angle. Recent applications of triple-axis diffraction, where an analyzer crystal is used after the specimen, to the study of very thin single epitaxial layers and multiquantum well structures are reviewed.

scholarly journals Relating Linear Energy Transfer to the Formation and Resolution of DNA Repair Foci After Irradiation with Equal Doses of X-ray Photons, Plateau, or Bragg-Peak Protons

2018 ◽  
Vol 19 (12) ◽  
pp. 3779 ◽  
Author(s):  
Sebastian Oeck ◽  
Klaudia Szymonowicz ◽  
Gesa Wiel ◽  
Adam Krysztofiak ◽  
Jamil Lambert ◽  
...  
Keyword(s):  
Dna Damage ◽  
Energy Transfer ◽  
Linear Energy Transfer ◽  
Bragg Peak ◽  
Cultured Cells ◽  
Human Cancer ◽  
Proton Beam Therapy ◽  
X Ray ◽  
Cellular Repair ◽  
Set Up

Proton beam therapy is increasingly applied for the treatment of human cancer, as it promises to reduce normal tissue damage. However, little is known about the relationship between linear energy transfer (LET), the type of DNA damage, and cellular repair mechanisms, particularly for cells irradiated with protons. We irradiated cultured cells delivering equal doses of X-ray photons, Bragg-peak protons, or plateau protons and used this set-up to quantitate initial DNA damage (mainly DNA double strand breaks (DSBs)), and to analyze kinetics of repair by detecting γH2A.X or 53BP1 using immunofluorescence. The results obtained validate the reliability of our set-up in delivering equal radiation doses under all conditions employed. Although the initial numbers of γH2A.X and 53BP1 foci scored were similar under the different irradiation conditions, it was notable that the maximum foci level was reached at 60 min after irradiation with Bragg-peak protons, as compared to 30 min for plateau protons and photons. Interestingly, Bragg-peak protons induced larger and irregularly shaped γH2A.X and 53BP1 foci. Additionally, the resolution of these foci was delayed. These results suggest that Bragg-peak protons induce DNA damage of increased complexity which is difficult to process by the cellular repair apparatus.

scholarly journals The first X-ray diffraction measurements on Mars

IUCrJ ◽  
2014 ◽  
Vol 1 (6) ◽  
pp. 514-522 ◽  
Author(s):  
David Bish ◽  
David Blake ◽  
David Vaniman ◽  
Philippe Sarrazin ◽  
Thomas Bristow ◽  
...  
Keyword(s):  
Field Studies ◽  
Central Peak ◽  
Chemical Compositions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters ◽  
Gale Crater ◽  
Quantitative Mineralogy ◽  
Transmission Geometry ◽  
Two Samples

The Mars Science Laboratory landed in Gale crater on Mars in August 2012, and the Curiosity rover then began field studies on its drive toward Mount Sharp, a central peak made of ancient sediments. CheMin is one of ten instruments on or inside the rover, all designed to provide detailed information on the rocks, soils and atmosphere in this region. CheMin is a miniaturized X-ray diffraction/X-ray fluorescence (XRD/XRF) instrument that uses transmission geometry with an energy-discriminating CCD detector. CheMin uses onboard standards for XRD and XRF calibration, and beryl:quartz mixtures constitute the primary XRD standards. Four samples have been analysed by CheMin, namely a soil sample, two samples drilled from mudstones and a sample drilled from a sandstone. Rietveld and full-pattern analysis of the XRD data reveal a complex mineralogy, with contributions from parent igneous rocks, amorphous components and several minerals relating to aqueous alteration. In particular, the mudstone samples all contain one or more phyllosilicates consistent with alteration in liquid water. In addition to quantitative mineralogy, Rietveld refinements also provide unit-cell parameters for the major phases, which can be used to infer the chemical compositions of individual minerals and, by difference, the composition of the amorphous component.

scholarly journals Characterization of individual stacking faults in a wurtzite GaAs nanowire by nanobeam X-ray diffraction

2017 ◽  
Vol 24 (5) ◽  
pp. 981-990 ◽  
Author(s):  
Arman Davtyan ◽  
Sebastian Lehmann ◽  
Dominik Kriegner ◽  
Reza R. Zamani ◽  
Kimberly A. Dick ◽  
...  
Keyword(s):  
Bragg Peak ◽  
Stacking Faults ◽  
Growth Direction ◽  
X Ray Diffraction ◽  
X Ray ◽  
Patterson Function ◽  
Transmission Electron ◽  
Gaas Nanowires ◽  
Gaas Nanowire

Coherent X-ray diffraction was used to measure the type, quantity and the relative distances between stacking faults along the growth direction of two individual wurtzite GaAs nanowires grown by metalorganic vapour epitaxy. The presented approach is based on the general property of the Patterson function, which is the autocorrelation of the electron density as well as the Fourier transformation of the diffracted intensity distribution of an object. Partial Patterson functions were extracted from the diffracted intensity measured along the [000\bar{1}] direction in the vicinity of the wurtzite 00\bar{1}\bar{5} Bragg peak. The maxima of the Patterson function encode both the distances between the fault planes and the type of the fault planes with the sensitivity of a single atomic bilayer. The positions of the fault planes are deduced from the positions and shapes of the maxima of the Patterson function and they are in excellent agreement with the positions found with transmission electron microscopy of the same nanowire.

Fourier Transformation of X-Ray Rocking Curves from Interferometer Structures

1993 ◽  
Vol 37 ◽  
pp. 135-144
Author(s):  
J. M. Hudson ◽  
B. K. Tanner ◽  
R. Blunt
Keyword(s):  
Layer Thickness ◽  
Bragg Peak ◽  
Noisy Data ◽  
X Ray Diffraction ◽  
Interference Structure ◽  
X Ray ◽  
Auto Correlation ◽  
Interference Fringes ◽  
Spline Fitting ◽  
Cubic Spline Fitting

AbstractWe discuss the use of Fourier transform techniques to extract layer thickness from the interference fringes observed in high resolution X-ray diffraction rocking curves of pseudomorphic HEMT structures. The interference structure is extracted by cubic spline fitting to the extrema of the data, thereby obtaining a background envelope which is used to normalise the data. The resulting constant background is subtracted from the data and the residual Fourier transformed. Auto correlation of the residual significantly improves the result from noisy data. Satisfactory results are obtained only when the Bragg peak from the substrate is windowed out. With a limited dynamic and angular range, there is often insufficient data to separate the two closely spaced periods arising from the total layer thickness and that excluding the quantum well. The result then corresponds to the average of these two thicknesses.

scholarly journals Irreversible Structural Transformation of five fold i-AlPdMn Quasicrystals after Ion Bombardment and Annealing

2000 ◽  
Vol 643 ◽  
Author(s):  
F. Schmithüsen ◽  
G. Cappello ◽  
S. Decossas ◽  
G. Torricelli ◽  
T.-L. Lee ◽  
...  
Keyword(s):  
High Resolution ◽  
Structural Transformation ◽  
Bragg Peak ◽  
Normal Incidence ◽  
Ion Bombardment ◽  
Sample Surface ◽  
Bulk Sample ◽  
X Ray Diffraction ◽  
Energy Position ◽  
X Ray

AbstractFive fold i-AlPdMn surface prepared under UHV by ion bombardment and annealing was so far considered to be bulk terminated. This result was substantially based on a quantitative LEED analyses [1]. Analysis of the specular rod in a X ray diffraction experiment at grazing incidence supported this result [2]. We present a new study of this surface by high resolution X ray diffraction at normal incidence. In this Bragg configuration the diffraction peak 18 – 29 for instance is at a photon energy of 2.873keV, the 72 – 116 reflection at 5.725keV. This results in an analyzed thickness of the sample surface of a few micrometers.The surface was cleaned by ion bombardment. During annealing (T≅880K), we clearly observed the progressive disappearance of the initial Bragg peak characteristic of the as cast bulk sample. Conversely a new Bragg peak grows at an energy position shifted by 1eV compared to the position of the original Bragg peak. This is a clear signature for an irreversible structural transformation which takes place on at least the micron thickness. On the transformed surface, both, a LEED pattern and a RHEED pattern, characteristic for a five fold surface were easily obtained.This high resolution experiment (the relative Bragg peak shift is 3ׁ10−4) was reproduced on samples from different initial compositions. This shows that five fold i-AlPdMn surface changes after preparation by ion bombardment and annealing at 900K on a micrometer thickness. This is not consistent with the conclusion that the surface is simply terminated by a cut of the original bulk. We conclude that a reorganization process of the quasicrystalline structure during annealing proceeds in the surface vicinity (probed depth is close to a few microns).

Oscillatory Resonant X-Ray Magnetic Bragg-Peak Signs and Gd Moments Induced by the Fe/Gd Interlayer Exchange Interaction

2002 ◽  
Vol 41 (Part 1, No. 1) ◽  
pp. 103-106 ◽  
Author(s):  
Hiromasa Sano ◽  
Hiroo Hashizume ◽  
Hiroshi Okuda ◽  
Nobuyoshi Hosoito
Keyword(s):  
Exchange Interaction ◽  
Bragg Peak ◽  
X Ray ◽  
Interlayer Exchange

Real-time x-ray scattering study of homoepitaxial growth of SrTiO3 by sputtering

2002 ◽  
Vol 749 ◽  
Author(s):  
Hsin-Yi Lee ◽  
C.-H. Hsu ◽  
Y.-W. Hsieh ◽  
K. S. Liang
Keyword(s):  
Real Time ◽  
Bragg Peak ◽  
Epitaxial Relationship ◽  
X Ray ◽  
Homoepitaxial Growth ◽  
X Ray Scattering ◽  
Scattering Study ◽  
Sputter Deposited ◽  
Ray Scattering

ABSTRACTThe real-time x-ray scattering measurements under in-situ sputtering conditions were employed to study the growth behavior of sputter-deposited SrTiO3 films on SrTiO3 (001) substrate. A condition for conformal growth between deposited layers and substrate was found by observing the oscillation fringe in the diffuse scattering of measured reflectivity. The azimuthal scan around surface Bragg peak of the film peak shows that the epitaxial relationship between film and substrate can be achieved by sputtering.

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