scholarly journals Correction factors in the photographic measurements of x-ray intensities in crystal analysis

1930 ◽  
Vol 127 (804) ◽  
pp. 71-88 ◽  
Keyword(s):  
Background Radiation ◽  
Complete Solution ◽  
Special Technique ◽  
X Rays ◽  
X Ray ◽  
Intensity Measurements ◽  
Integrated Intensity ◽  
Lattice Planes ◽  
Complex Crystals ◽  
Lengthy Operation

For the complete solution of the structures of complex crystals, and in particular of organic substances, it is essential to be able to measure at least the relative intensities of reflexion of homogeneous X-rays from the more important lattice planes with some degree of accuracy. In most crystal problems a number of parameters governing the positions of the atoms in the lattice remain to be found after the geometrical requirements of the symmetry have been satisfied. These can only be determined from intensity measurements, so that in general, the greater the number of reflexions measured, the more closely will the deduced structure approach to the truth. Until comparatively recently the only instrument of precision available for X-ray intensity work has been the Bragg ionisation spectrometer. It has, however, three disadvantages when used for this purpose, which may be briefly summarised:— (1) Only the strongest planes are measurable with any degree of accuracy, owing to the “swamping” effect of the unremovable background radiation in the case of the weaker reflexions. (2) It is clearly impossible to use it, without very special technique, in the case of crystals which are volatile or even liquid at normal temperatures. (3) The measurement of the true integrated intensity is a somewhat lengthy operation in practice, with the result that experimenters are tempted to determine the peak values of the intensities instead; these, in general, are not in the same ratio as the integrated reflexions, so that a false idea of the reflexions may be obtained.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

Detection of a metallic glass layer by x-ray diffraction

1986 ◽  
Vol 1 (5) ◽  
pp. 629-634 ◽  
Author(s):  
J.W. McCamy ◽  
M.J. Godbole ◽  
A.J. Pedraza ◽  
D.H. Lowndes
Keyword(s):  
Target Material ◽  
Amorphous Layer ◽  
Glass Layer ◽  
X Rays ◽  
Average Thickness ◽  
X Ray Diffraction ◽  
Near Surface ◽  
X Ray ◽  
Integrated Intensity ◽  
Thickness Measurements

A simple, precise method for obtaining the average thickness of an amorphous layer formed by any surface treatment has been developed. The technique uses an x-ray diffractoeter to measure the reduction in the integrated intensity of several diffracted x-ray lines due to the near surface amorphous layer. The target material for generation of x rays is selected so that the emitted x rays are strongly absorbed by the specimen. This method permits thickness measurements down to ∼ 100 nm. It has been tested on a specimen of Fe80B20 on which an amorphous layer was produced by pulsed XeCl (308 nm) laser irradiation; the amorphous layer thickness was found to be 1.34 (∼0.1) um.

X-Ray Determination of Site Occupation Parameters in Ordered Ternaries Cu(Aux.M1x.)M = Ni,Pd

1990 ◽  
Vol 213 ◽  
Author(s):  
R. Kumar ◽  
C. J. Sparks ◽  
T. Shiraishi ◽  
E.D. Specht ◽  
P. Zschack ◽  
...  
Keyword(s):  
Rietveld Method ◽  
Scattering Data ◽  
X Rays ◽  
X Ray ◽  
Site Occupation ◽  
Intensity Measurements ◽  
X Ray Scattering ◽  
Chemical Phase ◽  
Multiple Wavelengths ◽  
Scattering Factor

ABSTRACTX-ray scattering data obtained for multiple wavelengths with synchrotron radiation were analyzed by the Rietveld method to determine Ni and Pd distributions on the Cu(000) and Au(½½½) sites in the CuAuI tetragonal P4/mmm structure. Alloys of CuAuxM1-x containing 6 at. % Ni or 10 and 25 at. % Pd were processed to obtain maximum ordering. Nickel is predominantly found on the Cu site and most all the Pd is found on the Au site. The uncertainty in site occupation parameters is discussed for various contributions which affect powder intensity measurements. For highly absorbing materials, an observed powder roughness effect decreases the low angle (2θ) intensities relative to the high 2θ intensities. This effect reduces the reliability of the thermal parameters and obscures a proper description of the thermal motion of the two sublattices. Corrections to the X-ray intensity data for surface roughness/porosity effects reduce uncertainties to about ±1 at. % on the refined value of the site occupations. This use of variable wavelength X-rays with simultaneous refinement of the corresponding data is capable of distinguishing site occupations even between two elements of almost equal scattering factor as, for example, Cu and Ni atoms in this investigation. Chemical phase stability is related to the site occupation parameters.

X-Ray Diffraction

2021 ◽  
pp. 408-480
Author(s):  
Kannan M. Krishnan
Keyword(s):  
Point Group ◽  
Polycrystalline Materials ◽  
X Rays ◽  
X Ray Diffraction ◽  
Symmetry Point Group ◽  
X Ray ◽  
Atomic Scattering ◽  
Scattering Factor ◽  
Diffraction Patterns ◽  
Lattice Planes

X-rays diffraction is fundamental to understanding the structure and crystallography of biological, geological, or technological materials. X-rays scatter predominantly by the electrons in solids, and have an elastic (coherent, Thompson) and an inelastic (incoherent, Compton) component. The atomic scattering factor is largest (= Z) for forward scattering, and decreases with increasing scattering angle and decreasing wavelength. The amplitude of the diffracted wave is the structure factor, F hkl, and its square gives the intensity. In practice, intensities are modified by temperature (Debye-Waller), absorption, Lorentz-polarization, and the multiplicity of the lattice planes involved in diffraction. Diffraction patterns reflect the symmetry (point group) of the crystal; however, they are centrosymmetric (Friedel law) even if the crystal is not. Systematic absences of reflections in diffraction result from glide planes and screw axes. In polycrystalline materials, the diffracted beam is affected by the lattice strain or grain size (Scherrer equation). Diffraction conditions (Bragg Law) for a given lattice spacing can be satisfied by varying θ or λ — for study of single crystals θ is fixed and λ is varied (Laue), or λ is fixed and θ varied to study powders (Debye-Scherrer), polycrystalline materials (diffractometry), and thin films (reflectivity). X-ray diffraction is widely applied.

scholarly journals Differences in the directions of ejection of x-ray photo-electrons from various atomic levels

1929 ◽  
Vol 126 (800) ◽  
pp. 138-143 ◽  
Keyword(s):  
Resolving Power ◽  
X Rays ◽  
Expansion Chamber ◽  
X Ray ◽  
Chamber Method ◽  
Heavy Atoms ◽  
Intensity Measurements ◽  
The Individual ◽  
Radio Corporation Of America ◽  
Slow Electrons

Very valuable studies of the directions in which photo-electrons are ejected by X-rays have been made recently by Williams, Auger, and Anderson. All of these observers, however, used the C. T. R. Wilson expansion-chamber method which, in spite of its power in working with the individual electron, suffers from the disadvantage that the particular energy level in the atom from which the electron is ejected in general cannot be determined. It is true that in the case of heavy atoms such as xenon and bromine, Auger and Anderson succeeded, through the use of X-rays of particular energies, in distinguishing the electrons thrown out of the K level from those thrown out of the L levels, but to go much further in this direction by the expansion-chamber method (and, for example, to distinguish the L I from the L II or L III electrons) seems hopeless. Consequently, the magnetic spectrograph developed by one of us for studying the velocity of the X-ray electrons as a function of the angle of emission was applied to the problem with the results which it is the purpose of this paper to describe. We, as yet, have not succeeded in determining the actual directions of ejection with the precision which has been attained in the expansion-chamber method, but the resolving power of the apparatus for velocities is so large that the particular level in which each electron group originates is in general quite unambiguous. A description of the apparatus used and the procedure followed has been given in the paper referred to above and need not be repeated here. Ballast lamps of the sort developed at the General Electric Company and sold by the Radio Corporation of America (radiotron UV-886) have proved very useful in holding the current through the solenoid which produces the magnetic field constant during the long exposures (100-200 hours) which are necessary. Eastman X-ray plates were used throughout, as they have been found to be the most sensitive of any so far tried (except Schumann plates which are much too irregular for intensity measurements). The work has been seriously handicapped by the lack of sensibility of the photographic plates for slow electrons and by their rapid falling off in sensibility for electrons of velocities below about 12,000 volts. X-ray tubes with silver, molybdenum and copper anticathodes were used. The characteristic radiation from copper is, however, in spite of its intrinsic intensity, too soft to eject electrons with sufficient velocity to give photographic results in a reasonable length of time with the apparatus used. All the results shown below consequently were obtained with the characteristic rays of either silver or molybdenum.

Direct observation of various reaction pathways of arylnitrenes in different crystal environments caused by acid–base complex formation

2010 ◽  
Vol 66 (6) ◽  
pp. 647-661 ◽  
Author(s):  
Takahiro Mitsumori ◽  
Akiko Sekine ◽  
Hidehiro Uekusa ◽  
Yuji Ohashi
Keyword(s):  
Complex Formation ◽  
Structural Changes ◽  
Uv Light ◽  
Reaction Pathway ◽  
Crystal Form ◽  
X Rays ◽  
Acid Base ◽  
Base Complex ◽  
X Ray ◽  
Complex Crystals

The structures of reaction intermediates, arylnitrenes and their final products have been successfully analyzed by X-rays using acid–base complex formation. The acid–base complexes of 2-azidobenzoic acid (2a), 3-azidobenzoic acid (3a) and 4-azidobenzoic acid (4a) were made with dibenzylamine (db), N-benzyl-2-phenylethylamine (bp) and dicyclohexylamine (dc). For the complex crystals of (3a) and db (3a-db), and (4a) and db (4a-db) two forms of (I) and (II) were obtained. Eight types of complex crystals, (2a-db), (3a-db-I), (3a-db-II), (3a-dc), (4a-db-I), (4a-db-II), (4a-bp) and (4a-dc), suitable for X-ray analysis were obtained. When the crystals were irradiated with UV light at low temperatures, the reactions proceeded keeping the single-crystal form in the five crystals (2a-db), (3a-db-I), (3a-db-II), (3a-dc) and (4a-bp). Less than 25% of each azidobenzoic acids was transformed into an arylnitrene and dinitrogen. In three crystals the arylnitrenes produced gave new final products; 2,1-benzisoxazolone was observed for (2a-db) and trans-azobenzenes (i.e. dimerized nitrenes) were obtained for (3a-db-II) and (4a-bp). For (3a-db-I) and (3a-dc) the intermediate arylnitrenes were observed but did not transform to new products. All the structural changes were directly observed by X-ray analysis because the incomplete reactions occurred with retention crystallinity. The crystal environment, including the hydrogen bonding between the benzoic acid and the amine, places restrictions on the movement of the arylnitrene and influences the reaction pathway followed for conversion of the arylnitrene to its final product.

Investigation of Elemental Analysis of Water Samples by Radioalpha Induced X-Ray Emission Spectroscopy*

1974 ◽  
Vol 18 ◽  
pp. 333-342
Author(s):  
R. Hight ◽  
C. C. Foster
Keyword(s):  
Water Samples ◽  
Background Radiation ◽  
Trace Element Analysis ◽  
Alpha Particles ◽  
Particle Accelerators ◽  
X Rays ◽  
Element Analysis ◽  
Worst Case ◽  
Helium Atmosphere ◽  
X Ray

AbstractAlpha particles and protons from charged particle accelerators and photons from both x-ray tubes and radioactive sources have been shown to be useful for the excitation of characteristic x-rays for multi-element energy dispersive trace analysis of environmental samples to the few ppm range. We have investigated the use of 4.5 MeV alpha particles from a thin window Po-210 source of 5 mCi effective strength to directly excite x-rays from trace elements in 1 cc water samples evaporated on 1.75 mg/cm2 thick mylar backings in a helium atmosphere in a lucite enclosure. Minimum detectable amounts (MDA's) were established for 19 elements (22 ≤ Z ≤ 82) using K-, L- and M- radiation and 50 minute counting times. The smallest MDA determined was 0.11 μg for vanadium. Other representative MDA's, in μg, are Fe-0.54, Mo-0.31 and Pb-0.43. MDA's lower by an average factor of about 10 over an eight month source life would result from the use of 1 Ci of Po-210 for 50 minutes per sample. Thinner sample backings and improved source encapsulation will reduce background radiation and further improve sensitivity. Comparison of our MDA's (5 mCi-Po-210) with those of Blasius et al., who used radiophoton sources and 40,000 sec. counting times to determine trace metal pollutants in water samples, shows radioalpha excitation to have comparable sensitivity in the worst case, arsenic and better, by more than two orders of magnitude, sensitivity in the best case, vanadium.Radioalpha induced x-ray trace element analysis offers the same advantages of portability, ease of operation, low maintenance and cost, and "in house" availability as radiophoton induced analysis. Because of the availability of more intense sources (up to 10 Ci), the fact that the detected radiation (x-rays) differs from the excitation radiation (a-particles) and that K, L, and M x-ray emission cross-sections depend essentially only on the emitted x-ray energy, lower MDA's are obtainable for many elements in thin samples for comparable counting times, as well.

X-Ray Absroption Table for the 2-to-200 Å Region

1969 ◽  
Vol 13 ◽  
pp. 639-665 ◽  
Author(s):  
B. L, Henke and ◽  
R. L. Elgin
Keyword(s):  
Extreme Ultraviolet ◽  
Bragg Reflection ◽  
Pulse Height ◽  
X Rays ◽  
Temperature Plasma ◽  
X Ray ◽  
Langmuir Blodgett ◽  
Intensity Measurements ◽  
Measured Absorption ◽  
Physical And Chemical

Physical and chemical analysis, X-ray astronomy and high temperature plasma diagnostics which utilize the ultrasoft X-radiations hare made evident a strong need for filling the gap in measured absorption coefficient data for the radiations between the conventional X-rays and the extreme ultraviolet. More than one hundred new coefficients have been measured in this laboratory on the gas state, atomic or molecular, containing He, C, N, 0, F, Ne, S, Cl, Ar, Kr and Xe using eleven fluorescent, characteristic wavelengths Al-Kα (8.34 A) through Be-K (113.8 A). The radiations were isolated by Bragg reflection from multilayer analyzers of the Langmuir-Blodgett type and by pulse height discriminating proportional counter intensity measurements.

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