scholarly journals X-ray Propagation in Strongly Magnetized Plasmas

1985 ◽  
Vol 38 (5) ◽  
pp. 715 ◽  
Author(s):  
JG Kirk ◽  
NF Cramer
Keyword(s):  
Refractive Index ◽  
Neutron Stars ◽  
Cross Section ◽  
Numerical Scheme ◽  
Strong Field ◽  
Magnetized Plasma ◽  
Dielectric Tensor ◽  
Absorption Cross ◽  
X Ray ◽  
New Treatment

A new treatment of the calculation of the dielectric tensor of a magnetized plasma in an extremely strong field, such as occurs in magnetized neutron stars, is presented. An accurate numerical scheme for the evaluation of the hermitian and antihermitian parts of the tensor is used to calculate the refractive index and absorption cross section for magnetic fields and plasma temperatures typical of pulsating X-ray sources and y-ray burst sources.

scholarly journals Anisotropy of X-ray Absorption Cross Section in CeCoGe3 Single Crystal

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 544
Author(s):  
Andrei Rogalev ◽  
Fabrice Wilhelm ◽  
Elena Ovchinnikova ◽  
Aydar Enikeev ◽  
Roman Bakonin ◽  
...  
Keyword(s):  
Cross Section ◽  
Absorption Cross Section ◽  
Linear Dichroism ◽  
X Rays ◽  
Absorption Cross ◽  
X Ray ◽  
Measured Absorption ◽  
Linearly Polarized ◽  
X Ray Absorption ◽  
Absorption Edges

Absorption spectra of two orthogonal linearly polarized x-rays in a single CeCoGe3 crystal were measured at the ID12 beamline of the ESRF for the energies near the K-edges of Ge, Co and near the L23 edges of Ce. The X-ray natural linear dichroism (XNLD) was revealed in the vicinity of all the absorption edges, which indicates a splitting of electronic states in a crystalline field. Mathematical modelling in comparison with experimental data allowed the isotropic and anisotropic parts of atomic absorption cross section in CeCoGe3 to be determined near all measured absorption edges. The calculations also show that the “average” anisotropy of the cross section close to the Ge K-edge revealed in the experiment is less than the partial anisotropic contributions corresponding to Ge atoms in two different Wyckoff positions.

scholarly journals X-ray Spectroscopy of Thermally Emitting Neutron Stars

2004 ◽  
Vol 218 ◽  
pp. 283-286 ◽  
Author(s):  
M. H. van Kerkwijk
Keyword(s):  
Neutron Stars ◽  
Quantum Electrodynamics ◽  
Strong Field ◽  
Mode Conversion ◽  
X Ray ◽  
Surface Emission ◽  
Similar Temperature ◽  
Cyclotron Line ◽  
Absorption Features ◽  
Proton Cyclotron

I describe recent high-resolution X-ray spectroscopy of surface emission from nearby, thermally emitting neutron stars. I focus on RX J0720.4−3125, RX J1308.6+2127 and RX J1605.3+3249, all of which have similar temperature, but differ in the presence and strength of absorption features in their spectrA. I discuss possible causes for the absorption we see in two sources, and conclude that it may be proton cyclotron line absorption, but weakened due to the strong-field quantum electrodynamics effect of vacuum resonance mode conversion.

Multiple Scattering Calculations Applied to XAS: A Structure and Electronic Sensitive Tool

1991 ◽  
Vol 253 ◽  
Author(s):  
Philippe Sainctavit ◽  
J. Petiau
Keyword(s):  
Multiple Scattering ◽  
Cross Section ◽  
Absorption Cross Section ◽  
Scattering Theory ◽  
Spectral Features ◽  
Absorption Cross ◽  
Multiple Scattering Theory ◽  
X Ray ◽  
Sensitive Tool ◽  
X Ray Absorption

ABSTRACTWe present an application of multiple scattering theory with “muffin-tin” potentials to the calculation of X-ray absorption cross section. We have measured and calculated the K-edge spectra of atoms in compounds with zincblende structure : SiC, ZnS. We show that some spectral features can be precisely related to the local environnement around the absorbing atom.

X-Ray Absorption Studies of La2−xSrxCuO4 and Y1−xPrxBa2Cu3O7-δ

1987 ◽  
Vol 99 ◽  
Author(s):  
E. E. Alp ◽  
G. K. Shenoy ◽  
L. Soderholm ◽  
G. L. Goodman ◽  
D. G. Hinks ◽  
...  
Keyword(s):  
Rare Earth ◽  
Cross Section ◽  
Atomic Clusters ◽  
Oxide Superconductors ◽  
Absorption Cross ◽  
Edge Structure ◽  
X Ray ◽  
Absorption Studies ◽  
High Transition ◽  
X Ray Absorption

ABSTRACTThe question of valence of Cu and rare-earth atoms in the newly discovered oxide superconductors with high transition temperatures is crucial to the understanding of their electronic structure. We have measured the X-Ray Absorption Near Edge Structure (XANES) of Cu K transition and Pr Ljjj transition to obtain information on the valence of Cu, and Pr in La2−xSrxCuO4 and Y1−xPrxBa2Cu3O7-δ. We will present the experimental results, compare them with calculations of absorption cross-section for model atomic clusters, and discuss the valence of Cu as a function of oxygen concentration.

Maximum Cross Sections for Excited State and Two-Photon Absorption

1999 ◽  
Vol 597 ◽  
Author(s):  
Roger J. Becker
Keyword(s):  
Refractive Index ◽  
Cross Section ◽  
Cross Sections ◽  
Single Photon ◽  
Line Strength ◽  
Nonlinear Coefficient ◽  
Photon Absorption ◽  
Nonlinear Phenomena ◽  
Absorption Cross ◽  
Maximum Value

AbstractThere is a maximum value for any nonlinear process, which can be found on the basis of fundamental quantum mechanics. With regard to single photon processes, there is a maximum absorption cross section, σa, which any molecule may reach. The maximum is 1.13 × 10-17 λ is the wavelength of the light, n is the refractive index of the host medium, and Q is the quality factor ascribed to the absorption line width. Thus large cross sections can only be obtained at the expense of a narrow operating range. The maximum is set by fundamental physics. Since nonlinear phenomena are highly resonant, the maxima of higher-order processes are also a strong function of the width of the resonance and the peak wavelength. In the case of twophoton absorption the peak value of the maximum cross section, σ2N or δ, is roughly 3.5 × 10-32 λ4nQ cm4/GW, or about 7 × 10-57 λ3 nQ cm4/photon. No value for a nonlinear coefficient is meaningful in the absence of the width of the resonance, the wavelength, and the refractive index of the medium at the wavelength of the measurement.The basic quantity of interest is the linear electronic polarizability. This fundamental quantity determines not only the absorption for the various processes of interest, but also the surface tension and the closely related solubility parameter. All scale with the polarizability a. The polarizability has a maximum value of e2/mω2; consequently the absorption cross sections have a corresponding ceiling. The maximum value for the peak in a resonant polarizability curve is set by a balance between the Coulomb potential energy of the electron and its kinetic energy. Hence it is an inherent property of the electron itself, irrespective of the molecular orbital in which it finds itself. All that the particular quantum configuration of the molecule does is partition the line strength for absorption among various possible transitions. The extreme case is when virtually all the strength is concentrated in a single transition, an inherently resonant condition.

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