ON THE THEORY OF THE X-RAY DETERMINATION OF ELASTIC SCATTERING OF CATHODE RAYS

1934 ◽  
Vol 11 (2) ◽  
pp. 156-162
Author(s):  
Darol K. Froman
Keyword(s):  
Wave Length ◽  
Absolute Measurement ◽  
Theoretical Work ◽  
The Self ◽  
Solid Target ◽  
X Rays ◽  
Scattering Function ◽  
X Ray ◽  
Self Consistency

This paper is a continuation of Bubb's (1) theoretical work which relates the energies and momenta of cathode rays to the properties of X-ray photons produced by them. Bubb's results are used to determine a scattering function for the cathode rays in a target in terms of the intensities of X-rays of minimum wave-length emergent from the target at various angles to the incident cathode-ray stream. It is shown that the self-consistency of Bubb's results can be tested by measurements of the intensities of two components of these X-rays polarized in mutually perpendicular planes. Mention is made of an experiment now in progress designed to test Bubb's theory by an absolute measurement using a gaseous instead of a solid target.

scholarly journals Divergent-beam X-ray photography of crystals

1947 ◽  
Vol 240 (817) ◽  
pp. 219-250 ◽  
Keyword(s):  
Wave Length ◽  
Impurity Content ◽  
Type I ◽  
X Rays ◽  
Divergent Beam ◽  
X Ray ◽  
Air Temperatures ◽  
High Degree ◽  
Good Agreement

Divergent-beam X-ray photography of single crystals by transmission can be used to study the ‘extinction’, that is, the diminution of the transmitted radiation that takes place at the Bragg reflexion angles. The intensity and geometry of the absorption lines observed give useful information about the texture of the crystal. Divergent beam photographs have shown that many crystals of organic compounds are unexpectedly perfect, and that sudden cooling to liquid-air temperatures will increase the mosaic character of their structure by an important factor and make them more suitable for structural analysis by the usual methods. Type I diamonds, and natural ice even near to its melting-point, are also found to possess a high degree of perfection, which cannot be removed by liquid-air treatment. The divergent beam method may be used for the determination of orientation, but it is important that the wave-length of X-rays employed should be correctly related to the size and nature of the crystal. In certain favourable cases it is possible to make precision measurements of lattice constant or of wave-length from divergent beam photographs, without the use of any kind of precision apparatus. By such means it has been shown that the C—C distance in individual diamonds varies from 1541.53(± 0-02) to 1541.27X, (1.54465-1-54440A), a difference presumably due to varying impurity content. Using diamond and a brass anticathode, the Zn Ka 1 wave-length, relative to Cu K Ka 1 as 1537.40X, is found to be 1432.21 ( ± 0-04) X. Temperature control would improve the accuracy of this measurement, which is, however, in good agreement with the latest value obtained by orthodox precision methods.

scholarly journals On the ionization of light gases by X-rays. II.—The ionization of hydrogen by recoil electrons

1933 ◽  
Vol 141 (845) ◽  
pp. 686-696 ◽  
Keyword(s):  
Total Energy ◽  
Wave Length ◽  
Practical Importance ◽  
Incident Beam ◽  
Direct Methods ◽  
X Rays ◽  
Recoil Electron ◽  
X Ray ◽  
Experimental Errors

In Part I, p. 669, a technique has been described for determining the ratio of the ionization in a light gas (hydrogen or helium) to that in air when ionized by the same X-ray beam, homogeneous rays of medium wave-length and soft heterogeneous rays being available for the measurement. The ionization ratio can be converted into the ratio of the energies absorbed by the two gases by making use of the known value of the ratio of the energies required to form a pair of ions in the two gases; and since the ionization in air is due almost entirely to photoelectrons and the absorption coefficient is known, the energy in the incident beam can be obtained from the energy absorbed by air; thus the energy absorbed by the light gas can be correlated with the energy in the incident beam. The radiation of medium wave-length (about ½ A.) ionizes the light gas chiefly through the agency of recoil electrons, so that after applying a correction (obtained from the soft ray ratio) for the ionization due to photoelectrons, the fraction of the energy in the incident beam converted into recoil electron energy by the gas may be obtained, and compared with the predictions of the quantum theory of recoil scattering. In this paper the comparison is carried out with measurements on hydrogen, and for convenience it will be made between the experimental and calculated values of the ionization ratios. Excluding the early work of Shearer already mentioned in I no experimental determination of the total energy associated with recoil electrons has hitherto been made by any method as direct as the present one, though less direct methods have been employed. In general, however, the experimental technique was open to criticism, and the interpretation of the measurements uncertain, so that it is not surprising that the results were inconsistent either with one another or with theory. It is also possible to calculate the total energy associated with recoil electrons from other experimental facts concerning recoil scattering, but the experimental errors involved combine to make the final result very unreliable. The energy associated with recoil electrons is, however, not only of theoretical interest but also of great practical importance, since all effects arising from scattering, in the scattering substance itself, are due to recoil electron emission.

scholarly journals the atomic scattering power of iron for various X-ray wave-lengths

1932 ◽  
Vol 136 (829) ◽  
pp. 272-288 ◽  
Keyword(s):  
Energy Levels ◽  
Wave Length ◽  
X Rays ◽  
X Ray ◽  
Atomic Scattering Factor ◽  
Hard Radiation ◽  
Atomic Scattering ◽  
Scattering Factor ◽  
Dispersion Terms

Calculations of f , the atomic scattering factor of an element for X-rays, have hitherto been made on the assumption that the value of f for a given value of sin θ/λ is independent of wave-length. This assumption is only justified when the frequency of the X-rays is much greater than the characteristic frequency of any of the energy levels in the scattering atom. This condition is realised when a hard radiation such as Mo Kα is used in order to investigate crystals containing only light elements, such as aluminium. Under these conditions it has been found that absolute determination of f made experimentally give results in excellent agreement with theory. In many investigations, however, we are dealing with an entirely different set of conditions. For example, investigations of alloys are usually carried out with Cr, Fe or Cu radiation. Often the alloys contain Cr, Mn, Fe, Co, Ni, Cu or Zn, and the K absorption edge for each of these elements is near the wave-length of the radiation employed. Under these circumstances the conditions postulated by the simple theory no longer hold. Dispersion terms must now be introduced into the scattering formula, and we get an effect which may in some degree be compared with the anomalous dispersion of light.

scholarly journals Fine-structure of soft X-ray absorption edges - I—Li, Mg, Ni, Cu metals

1937 ◽  
Vol 161 (906) ◽  
pp. 420-440 ◽  
Keyword(s):  
Fine Structure ◽  
Conduction Electron ◽  
Wave Length ◽  
Ultra Violet ◽  
Short Wave ◽  
Experimental Investigations ◽  
X Rays ◽  
X Ray ◽  
X Ray Absorption

The borderland region between ultra-violet light and X-rays, particularly from about 100 to 300 A, is very suitable for obtaining spectroscopic information regarding the electronic structure of metals, or solids generally. The first step towards this problem consists in the determination of the intensity distribution in the soft X-ray emission bands, which represent transitions from the filled conduction-electron levels of a metal into a vacant inner shell. We thus obtain information relating to the distribution with energy of these filled levels. The most complete experimental investigations of the emission bands are those of Siegbahn and Magnusson (1934) and of O’Bryan and Skinner (1934) for the metals Li, Be, Na, Mg, Al, Si. Subse­quent work showed that the extension of these results to heavier metals is very difficult, because the Auger effect reduces the intensity of the emission by a large factor. The complementary problem is that of absorption, in which we are dealing with transitions from an inner shell of the metal into one of the unoccupied conduction-electron levels of the metal. The probability of such an absorption process is closely connected with the density of the unoccupied levels as a function of energy. The experimental problem therefore consists of the determination of the variation in the absorption coefficient of radiation by electrons of a given inner shell as a function of wave-length; or, as it may be called, the determination of the fine-structure on the short wave-length side of an X-ray absorption edge of a metal.

Problems in Thin-Film X-ray Quantification

1990 ◽  
Vol 48 (2) ◽  
pp. 458-459
Author(s):  
J N Chapman ◽  
W A P Nicholson
Keyword(s):  
Thin Film ◽  
Specimen Thickness ◽  
X Rays ◽  
Characteristic Peak ◽  
Local Composition ◽  
X Ray ◽  
Measured Ratio ◽  
Path Lengths ◽  
Composition Changes

Energy dispersive x-ray microanalysis (EDX) is widely used for the quantitative determination of local composition in thin film specimens. Extraction of quantitative data is usually accomplished by relating the ratio of the number of atoms of two species A and B in the volume excited by the electron beam (nA/nB) to the corresponding ratio of detected characteristic photons (NA/NB) through the use of a k-factor. This leads to an expression of the form nA/nB = kAB NA/NB where kAB is a measure of the relative efficiency with which x-rays are generated and detected from the two species.Errors in thin film x-ray quantification can arise from uncertainties in both NA/NB and kAB. In addition to the inevitable statistical errors, particularly severe problems arise in accurately determining the former if (i) mass loss occurs during spectrum acquisition so that the composition changes as irradiation proceeds, (ii) the characteristic peak from one of the minority components of interest is overlapped by the much larger peak from a majority component, (iii) the measured ratio varies significantly with specimen thickness as a result of electron channeling, or (iv) varying absorption corrections are required due to photons generated at different points having to traverse different path lengths through specimens of irregular and unknown topography on their way to the detector.

scholarly journals Electronic Excitations and Radiation Damage in Macromolecular Crystallography

Crystals ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 273 ◽  
Author(s):  
José Brandão-Neto ◽  
Leonardo Bernasconi
Keyword(s):  
Chemical Information ◽  
X Rays ◽  
Electronic Excitations ◽  
Macromolecular Crystallography ◽  
X Ray Diffraction ◽  
X Ray ◽  
Atomic Structures ◽  
Successful Approach ◽  
Structural Research

Macromolecular crystallography at cryogenic temperatures has so far provided the majority of the experimental evidence that underpins the determination of the atomic structures of proteins and other biomolecular assemblies by means of single crystal X-ray diffraction experiments. One of the core limitations of the current methods is that crystal samples degrade as they are subject to X-rays, and two broad groups of effects are observed: global and specific damage. While the currently successful approach is to operate outside the range where global damage is observed, specific damage is not well understood and may lead to poor interpretation of the chemistry and biology of the system under study. In this work, we present a phenomenological model in which specific damage is understood as the result of a single process, the steady excitation of crystal electrons caused by X-ray absorption, which acts as a trigger for the bulk effects that manifest themselves in the form of global damage and obscure the interpretation of chemical information from XFEL and synchrotron structural research.

scholarly journals Electronic Excitations and Radiation Damage in Macromolecular Crystallography

2018 ◽  
Author(s):  
José Brandão-Neto ◽  
Leonardo Bernasconi
Keyword(s):  
Chemical Information ◽  
X Rays ◽  
Electronic Excitations ◽  
Macromolecular Crystallography ◽  
X Ray Diffraction ◽  
X Ray ◽  
Atomic Structures ◽  
Successful Approach ◽  
Structural Research

Macromolecular crystallography at cryogenic temperatures has so far provided the majority of the experimental evidence that underpins the determination of the atomic structures of proteins and other biomolecular assemblies by means of single crystal X-ray diffraction experiments. One of the core limitations of the current methods is that crystal samples degrade as they are subject to X-rays, and two broad groups of effects are observed: global and specific damage. While the currently successful approach is to operate outside the range where global damage is observed, specific damage is not well understood and may lead to poor interpretation of the chemistry and biology of the system under study. In this work, we present a phenomenological model in which specific damage is understood as the result of a single process, the steady excitation of crystal electrons caused by X-ray absorption, which acts as a trigger for the bulk effects that manifest themselves in the form of global damage and obscure the interpretation of chemical information from XFEL and synchrotron structural research.

scholarly journals On the ionization of light gases by X-rays. I.—Technique

1933 ◽  
Vol 141 (845) ◽  
pp. 669-686
Keyword(s):  
Absolute Intensity ◽  
X Rays ◽  
X Ray ◽  
Quantitative Correlation ◽  
Quantitative Measurements ◽  
Fluorescent Radiation ◽  
A New Technique ◽  
Heavy Gas ◽  
Reliable Correlation

The measurement of the intensity of an X-ray beam in absolute units is in theory most satisfactorily accomplished by a determination of its heating effect. The method, however, is attended by considerable experimental difficulties, so that its application is very limited, and in practice it is usual to replace it by a determination of the ionization produced when the beam is passed through a gas. To correlate the ionization with an absolute intensity requires a quantitative knowledge of the details of the interaction between the X-rays and the molecules concerned and of the ionization of the gas by the ejected electrons. It sometimes happens that the processes involved about which we know least are relatively unimportant, so that a fairly reliable correlation can be made; and much work has been done on the application of the ionization method to X-ray dosimetry. But in general a quantitative correlation between ionization and intensity is not possible. A further study of the ionization of gases by X-rays is therefore desirable; moreover it may be made to yield important information concerning the processes involved. The early development of the physics of X-rays contains many examples of this, and more recently an important contribution has been made by Stockmeyer. The events leading to the ionization of a heavy gas are exceedingly complicated, whereas in the light gases (hydrogen and helium) some of these events are absent or else occur to a negligible extent, so that the interpretation of experiments with the latter becomes simpler and more reliable. These gases are therefore specially worthy of study. Moreover, for them the application of quantum mechanics leads to the most definite results for comparison with experiment, and in particular permits of a direct test of some aspects of Dirac’s theory of recoil scattering. The ionization due to the gas itself is, however, very small, and may even be less than the secondary ionization due to electrons liberated from the chamber walls. The technique used in ionization measurements with heavy gases is therefore unsuitable. Hitherto the only attempt made to extend such measurements to light gases is an experiment carried out in 1915 on hydrogen by Shearer who, however, obtained very variable results and an ionization markedly smaller than that to be expected from recoil electrons alone. Moreover his experimental method is now open to criticism in view of our greater knowledge of X-rays, and in particular the fluorescent radiation used was of doubtful homogeneity. The present paper will describe a new technique suitable for quantitative measurements of the ionization produced by X-rays in light gases, and in another paper it will be applied to a re-investigation of hydrogen.

To the question of the treatment of surgical tbc

1926 ◽  
Vol 22 (5-6) ◽  
pp. 737
Author(s):  
I. Friedland
Keyword(s):  
Fatty Acids ◽  
Adrenal Gland ◽  
Fish Oil ◽  
Healthy Subject ◽  
Normal State ◽  
Adrenal Glands ◽  
X Rays ◽  
Subcutaneous Injections ◽  
X Ray

Arikhbaev (Vesti. Khir., 1926, book 17-18), having established the normal state of the lipolytic index in 30 people with various diseases and then proceeding to the determination of lipase in the blood of 9 various patients and 1 healthy subject exposed to irritating doses of X-ray rays on the adrenal gland, which caused its hyperfunction, finished his research by observing 5 patients with various forms of surgical tuberculosis, of whom three underwent simultaneous x-rays of the adrenal glands with subcutaneous injections of fish oil neutralized from fatty acids, one - only injections of neutralized fish oil and one - only an operational aid.

scholarly journals The X-ray stellar population of the LMC

2008 ◽  
Vol 4 (S256) ◽  
pp. 20-29 ◽  
Author(s):  
Yaël Nazé
Keyword(s):  
Stellar Population ◽  
Main Sequence ◽  
Massive Stars ◽  
High Energy ◽  
Magellanic Clouds ◽  
X Rays ◽  
X Ray ◽  
Energy Domain ◽  
X Ray Binaries

AbstractIn the study of stars, the high energy domain occupies a place of choice, since it is the only one able to directly probe the most violent phenomena: indeed, young pre-main sequence objects, hot massive stars, or X-ray binaries are best revealed in X-rays. However, previously available X-ray observatories often provided only crude information on individual objects in the Magellanic Clouds. The advent of the highly efficient X-ray facilities XMM-Newton and Chandra has now dramatically increased the sensitivity and the spatial resolution available to X-ray astronomers, thus enabling a fairly easy determination of the properties of individual sources in the LMC.

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