scholarly journals Some Features of the Direct and Inverse Double-Compton Effect as Applied to Astrophysics

Physics ◽  
2021 ◽  
Vol 3 (4) ◽  
pp. 1167-1174
Author(s):  
Viktor Dubrovich ◽  
Timur Zalialiutdinov
Keyword(s):  
Cross Section ◽  
Spectral Characteristics ◽  
Plane Waves ◽  
Detailed Balance ◽  
Infrared Divergence ◽  
Matrix Formalism ◽  
X Ray ◽  
S Matrix ◽  
Infrared Divergences ◽  
Photon Source

In the present paper, the process of inverse double-Compton (IDC) scattering is considered in the context of astrophysical applications. It is assumed that the two hard X-ray photons emitted from an astrophysical source are scattered on a free electron and converted into a single soft photon of optical range. Using the QED S-matrix formalism for the derivation of a cross-section of direct double-Compton (DDC) scattering and assuming detailed balance conditions, an analytical expression for the cross-section of the IDC process is presented. It is shown that at fixed energies of incident photons, the inverse cross-section has no infrared divergences, and its behavior is completely defined by the spectral characteristics of the photon source itself, in particular by the finite interaction time of radiation with an electron. Thus, even for the direct process, the problem of resolving infrared divergence actually refers to a real physical source of radiation in which photons are never actually plane waves. As a result, the physical frequency profile of the scattered radiation for DDC as well as for IDC processes is a function of both the intensity and line shape of the incident photon field.

scholarly journals VUV and Soft X-ray Spectroscopy of Actinides

2003 ◽  
Vol 802 ◽  
Author(s):  
Clifford G. Olson ◽  
John J. Joyce ◽  
Tomasz Durakiewicz ◽  
Elzbieta Guziewicz ◽  
Martin Butterfield
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Spectral Characteristics ◽  
Electronic States ◽  
Momentum Dependence ◽  
Auger Electrons ◽  
X Ray ◽  
Relative Cross Section ◽  
Initial States ◽  
Valence Bands

ABSTRACTOptical and photoelectron spectroscopies using VUV and Soft X-ray photons are powerful tools for studies of elemental and compound actinides. Large changes in the relative atomic cross sections of the 5f, 6d and sp electrons allow decomposition of the character of the valence bands using photoemission. Resonant enhancement of photoelectrons and Auger electrons at the 5d core threshold further aids the decomposition and gives a measure of elemental specificity. Angle-resolved photoemission can be used to map the momentum dependence of the electronic states. The large changes in relative cross section with photon energy yields further details when the mapping is done at equivalent points in multiple zones. Spectra for well understood rare earth materials will be presented to establish spectral characteristics for known atomic character initial states. These signatures will be applied to the case of USb to investigate f-d hybridization near the Fermi level.

Resonance Widths and Unitarity

1972 ◽  
Vol 50 (2) ◽  
pp. 84-92 ◽  
Author(s):  
C. T. Tindle
Keyword(s):  
Energy Dependence ◽  
Cross Section ◽  
Matrix Theory ◽  
Neutron Cross Section ◽  
Matrix Formalism ◽  
R Matrix ◽  
Level Width ◽  
S Matrix ◽  
The Difference ◽  
Energy Dependent

The low energy neutron cross section of 135Xe is analyzed using both the R-matrix theory of Wigner and Eisenbud and the S-matrix theory of Humblet and Rosenfeld. Particular attention is given to the role played by the total resonance level width for it is well known that the R-matrix widths are energy dependent but the S-matrix widths are not. This different energy dependence leads to different analytic forms for the cross section and the n + 135Xe reaction offers what may be the simplest and best physical example for comparing these two forms. To the accuracy of the present data the difference is not detectable. The different energy dependence of the resonance widths is shown to be related to unitarity. A general proof that the R-matrix formalism is always unitary is given. The difficulty of satisfying unitarity in the S-matrix formalism is discussed and it is shown for the n + 135Xe reactions that this can lead to physically unacceptable solutions. This "lack of unitarity" does not, however, lead to any difficulties in fitting the present experimental data.

Angular variations of K and L X-ray fluorescence cross sections for some lanthanides

2008 ◽  
Vol 86 (2) ◽  
pp. 361-367 ◽  
Author(s):  
I Han ◽  
M Şahin ◽  
L Demir
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Emission Angle ◽  
X Rays ◽  
X Ray ◽  
Isotropic Distribution ◽  
Fluorescence Cross Section ◽  
Intensity Ratios ◽  
Experimental Values ◽  
Photon Source

Kα, Kβ, Lα, and Lβ X-ray fluorescence cross sections for lanthanides in the atomic range 62 ≤ Z ≤ 68 (Sm, Eu, Gd Tb, Dy, Ho, and Er) were simultaneously measured by 59.54 keV incident photon energy at five angles ranging from 120° to 160°. The measurements were performed using an Am-241 radioisotope as the photon source and a Si(Li) detector. The Lα X-ray fluorescence cross section (σLα) was found to decrease with increasing emission angle and showed an anisotropic distribution of Lα X-rays. Kα, Kβ, and Lβ X-ray fluorescence cross sections (σKα, σKβ, and σLβ) were observed to be angle-independent and showed an isotropic distribution of Kα, Kβ, and Lβ X-rays. The Kα and Kβ X-rays originate from filling of the K shell (J = 1/2) vacancies, Lβ X-rays from filling of the L1 and L2 (J = 1/2) subshell vacancies, and Lα X-rays from filling of the L3 subshell (J = 3/2) vacancy. The fluorescent X-rays originating from the vacancy states with J = 1/2 are isotropic and unpolarized, but fluorescent X-rays originating from the vacancy states with J > 1/2 are anisotropic and polarized. Thus, the atomic inner shells vacancy states with J > 1/2 are aligned whereas vacancy states with J = 1/2 are not aligned. Lα fluorescence X-rays have an anisotropic distribution, while Kα, Kβ, and Lβ fluorescence X-rays have isotropic distribution. Furthermore, the IKβ/IKα, ILα/IKα}, ILβ/IKα, and ILβ/ILα intensity ratios for the elements under investigation were determined. The experimental cross sections and intensity ratios for Kα, Kβ, Lα, and Lβ fluorescence X-rays were also determined, and these experimental values were compared with our calculated theoretical values.PACS Nos.: 32.30.Rj, 32.80.Cy

scholarly journals Quantum field-theoretical description of neutrino and neutral kaon oscillations

2018 ◽  
Vol 33 (13) ◽  
pp. 1850075 ◽  
Author(s):  
Igor P. Volobuev
Keyword(s):  
Plane Waves ◽  
Neutral Kaon ◽  
Theoretical Description ◽  
Matrix Formalism ◽  
Quantum Field ◽  
Time Intervals ◽  
Standard Quantum ◽  
Mass Eigenstates ◽  
Quantum Mechanical Description ◽  
S Matrix

It is shown that the neutrino and neutral kaon oscillation processes can be consistently described in quantum field theory using only plane waves of the mass eigenstates of neutrinos and neutral kaons. To this end, the standard perturbative S-matrix formalism is modified so that it can be used for calculating the amplitudes of the processes passing at finite distances and finite time intervals. The distance-dependent and time-dependent parts of the amplitudes of the neutrino and neutral kaon oscillation processes are calculated and the results turn out to be in accordance with those of the standard quantum mechanical description of these processes based on the notion of neutrino flavor states and neutral kaon states with definite strangeness. However, the physical picture of the phenomena changes radically: now, there are no oscillations of flavor or definite strangeness states, but, instead of it, there is interference of amplitudes due to different virtual mass eigenstates.

scholarly journals M sub-shell X-ray fluorescence cross-section measurements in high Z elements with X-ray tube photon source

2014 ◽  
Vol 5 (2) ◽  
pp. 363-369 ◽  
Author(s):  
Sheenu Gupta ◽  
Gurpreet Kaur ◽  
Himani Bansal ◽  
Vijay Kumar Mittal ◽  
Raj Mittal
Keyword(s):  
Cross Section ◽  
X Ray ◽  
Fluorescence Cross Section ◽  
Photon Source

Freeze-Fracture Replication of Frozen Outer Segments of Rat Retinal Rods

1969 ◽  
Vol 27 ◽  
pp. 392-393
Author(s):  
Thomas S. Leeson ◽  
C. Roland Leeson
Keyword(s):  
Electron Microscopy ◽  
Cross Section ◽  
Outer Segment ◽  
Freeze Fracture ◽  
X Ray Diffraction ◽  
X Ray ◽  
Outer Segments ◽  
Retinal Rods ◽  
Temperature Electron ◽  
Freeze Etching

Numerous previous studies of outer segments of retinal receptors have demonstrated a complex internal structure of a series of transversely orientated membranous lamellae, discs, or saccules. In cones, these lamellae probably are invaginations of the covering plasma membrane. In rods, however, they appear to be isolated and separate discs although some authors report interconnections and some continuities with the surface near the base of the outer segment, i.e. toward the inner segment. In some species, variations have been reported, such as longitudinally orientated lamellae and lamellar whorls. In cross section, the discs or saccules show one or more incisures. The saccules probably contain photolabile pigment, with resulting potentials after dipole formation during bleaching of pigment. Continuity between the lamina of rod saccules and extracellular space may be necessary for the detection of dipoles, although such continuity usually is not found by electron microscopy. Particles on the membranes have been found by low angle X-ray diffraction, by low temperature electron microscopy and by freeze-etching techniques.

Studies of metaphase chromosomes in the scanning transmission x-ray microscope: Image fidelity, radiation damage and specimen preparation

1992 ◽  
Vol 50 (2) ◽  
pp. 1038-1039
Author(s):  
Shawn Williams ◽  
Xiaodong Zhang ◽  
Susan Lamm ◽  
Jack Van’t Hof
Keyword(s):  
Visible Light ◽  
Radiation Damage ◽  
Cross Section ◽  
Imaging Techniques ◽  
Dose Range ◽  
Specimen Preparation ◽  
X Rays ◽  
Metaphase Chromosomes ◽  
X Ray ◽  
Scanning Transmission

The Scanning Transmission X-ray Microscope (STXM) is well suited for investigating metaphase chromosome structure. The absorption cross-section of soft x-rays having energies between the carbon and oxygen K edges (284 - 531 eV) is 6 - 9.5 times greater for organic specimens than for water, which permits one to examine unstained, wet biological specimens with resolution superior to that attainable using visible light. The attenuation length of the x-rays is suitable for imaging micron thick specimens without sectioning. This large difference in cross-section yields good specimen contrast, so that fewer soft x-rays than electrons are required to image wet biological specimens at a given resolution. But most imaging techniques delivering better resolution than visible light produce radiation damage. Soft x-rays are known to be very effective in damaging biological specimens. The STXM is constructed to minimize specimen dose, but it is important to measure the actual damage induced as a function of dose in order to determine the dose range within which radiation damage does not compromise image quality.

Searching for the causes why some of the paintings by Mihaly Munkacsy are darkening

1990 ◽  
Vol 48 (2) ◽  
pp. 204-205
Author(s):  
Imre Pozsgai ◽  
Klara Erdöhalmi-Torok
Keyword(s):  
Electron Beam ◽  
Cross Section ◽  
Polyester Resin ◽  
National Gallery ◽  
X Ray ◽  
Art Historians ◽  
Made In ◽  
Grinding And Polishing

The paintings by the great Hungarian master Mihaly Munkacsy (1844-1900) made in an 8-9 years period of his activity are deteriorating. The most conspicuous sign of the deterioration is an intensive darkening. We have made an attempt by electron beam microanalysis to clarify the causes of the darkening. The importance of a study like this is increased by the fact that a similar darkening can be observed on the paintings by Munkacsy’s contemporaries e.g Courbet and Makart. A thick brown mass the so called bitumen used by Munkacsy for grounding and also as a paint is believed by the art historians to cause the darkening.For this study, paint specimens were taken from the following paintings: “Studio”, “Farewell” and the “Portrait of the Master’s Wife”, all of them are the property of the Hungarian National Gallery. The paint samples were embedded in a polyester resin “Poly-Pol PS-230” and after grinding and polishing their cross section was used for x-ray mapping.

Fractionation of polymethylene chains: An electron crystallographic investigation

1986 ◽  
Vol 44 ◽  
pp. 794-795
Author(s):  
Douglas L. Dorset
Keyword(s):  
Cross Section ◽  
Binary Systems ◽  
Linear Chain ◽  
Pure Component ◽  
Organic Substrates ◽  
Crystallographic Investigation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molecular Sizes ◽  
The Stability

A variety of linear chain materials exist as polydisperse systems which are difficultly purified. The stability of continuous binary solid solutions assume that the Gibbs free energy of the solution is lower than that of either crystal component, a condition which includes such factors as relative molecular sizes and shapes and perhaps the symmetry of the pure component crystal structures.Although extensive studies of n-alkane miscibility have been carried out via powder X-ray diffraction of bulk samples we have begun to examine binary systems as single crystals, taking advantage of the well-known enhanced scattering cross section of matter for electrons and also the favorable projection of a paraffin crystal structure posited by epitaxial crystallization of such samples on organic substrates such as benzoic acid.

Low-voltage EDS of magnesium ferrite Dendrites in a FEG-SEM

1996 ◽  
Vol 54 ◽  
pp. 478-479
Author(s):  
Matthew T. Johnson ◽  
Ian M. Anderson ◽  
Jim Bentley ◽  
C. Barry Carter
Keyword(s):  
Monte Carlo ◽  
Quantitative Analysis ◽  
Monte Carlo Simulations ◽  
Cross Section ◽  
Spatial Resolution ◽  
Low Voltage ◽  
Magnesium Ferrite ◽  
X Ray ◽  
Interaction Volume ◽  
Ferrite Spinel

Energy-dispersive X-ray spectrometry (EDS) performed at low (≤ 5 kV) accelerating voltages in the SEM has the potential for providing quantitative microanalytical information with a spatial resolution of ∼100 nm. In the present work, EDS analyses were performed on magnesium ferrite spinel [(MgxFe1−x)Fe2O4] dendrites embedded in a MgO matrix, as shown in Fig. 1. spatial resolution of X-ray microanalysis at conventional accelerating voltages is insufficient for the quantitative analysis of these dendrites, which have widths of the order of a few hundred nanometers, without deconvolution of contributions from the MgO matrix. However, Monte Carlo simulations indicate that the interaction volume for MgFe2O4 is ∼150 nm at 3 kV accelerating voltage and therefore sufficient to analyze the dendrites without matrix contributions.Single-crystal {001}-oriented MgO was reacted with hematite (Fe2O3) powder for 6 h at 1450°C in air and furnace cooled. The specimen was then cleaved to expose a clean cross-section suitable for microanalysis.

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