Atomic-number dependence of the magnetic-sublevel population in the autoionization state formed in dielectronic recombination

Autoionization and dielectronic attachment are usually omitted from rate equations for the non–LTE average–atom model, causing systematic errors in predicted ionization states and electronic populations for atoms in hot dense plasmas produced by laser irradiation of solid targets. We formulate a method by which dielectronic recombination can be included in average–atom calculations without conflict with the principle of detailed balance. The essential new feature in this extended average atom model is a treatment of strong correlations of electron populations induced by the dielectronic attachment process.

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Thickness and composition determinations from T.E.M. specimens using both x-ray and backscattered electron data

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100112816 ◽

1984 ◽

Vol 42 ◽

pp. 576-577

Author(s):

M.D. Ball ◽

H. Lagace ◽

M.C. Thornton

Keyword(s):

Electron Microscope ◽

Atomic Number ◽

Transmission Electron Microscope ◽

Convenient Method ◽

Flow Chart ◽

X Ray ◽

Intensity Measurements ◽

Transmission Electron ◽

Electron Intensity ◽

Backscattered Electron

The backscattered electron coefficient η for transmission electron microscope specimens depends on both the atomic number Z and the thickness t. Hence for specimens of known atomic number, the thickness can be determined from backscattered electron coefficient measurements. This work describes a simple and convenient method of estimating the thickness and the corrected composition of areas of uncertain atomic number by combining x-ray microanalysis and backscattered electron intensity measurements.The method is best described in terms of the flow chart shown In Figure 1. Having selected a feature of interest, x-ray microanalysis data is recorded and used to estimate the composition. At this stage thickness corrections for absorption and fluorescence are not performed.

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Is there a “universal” MAC equation?

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134740 ◽

1990 ◽

Vol 48 (2) ◽

pp. 228-229

Author(s):

Robert E. Ogilvie

Keyword(s):

Absorption Coefficient ◽

Atomic Absorption ◽

Atomic Number ◽

X Ray ◽

Time Period ◽

Image Position

The search for an empirical absorption equation begins with the work of Siegbahn (1) in 1914. At that time Siegbahn showed that the value of (μ/ρ) for a given element could be expressed as a function of the wavelength (λ) of the x-ray photon by the following equationwhere C is a constant for a given material, which will have sudden jumps in value at critial absorption limits. Siegbahn found that n varied from 2.66 to 2.71 for various solids, and from 2.66 to 2.94 for various gases.Bragg and Pierce (2) , at this same time period, showed that their results on materials ranging from Al(13) to Au(79) could be represented by the followingwhere μa is the atomic absorption coefficient, Z the atomic number. Today equation (2) is known as the “Bragg-Pierce” Law. The exponent of 5/2(n) was questioned by many investigators, and that n should be closer to 3. The work of Wingardh (3) showed that the exponent of Z should be much lower, p = 2.95, however, this is much lower than that found by most investigators.

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Contribution of x-ray total reflection to the background intensity in EPMA

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134600 ◽

1990 ◽

Vol 48 (2) ◽

pp. 202-203

Author(s):

Werner P. Rehbach ◽

Peter Karduck

Keyword(s):

Atomic Number ◽

Target Material ◽

Total Reflection ◽

Background Intensity ◽

X Rays ◽

Characteristic Radiation ◽

X Ray

In the EPMA of soft x rays anomalies in the background are found for several elements. In the literature extremely high backgrounds in the region of the OKα line are reported for C, Al, Si, Mo, and Zr. We found the same effect also for Boron (Fig. 1). For small glancing angles θ, the background measured using a LdSte crystal is significantly higher for B compared with BN and C, although the latter are of higher atomic number. It would be expected, that , characteristic radiation missing, the background IB (bremsstrahlung) is proportional Zn by variation of the atomic number of the target material. According to Kramers n has the value of unity, whereas Rao-Sahib and Wittry proposed values between 1.12 and 1.38 , depending on Z, E and Eo. In all cases IB should increase with increasing atomic number Z. The measured values are in discrepancy with the expected ones.

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DIELECTRONIC RECOMBINATION IN THE AVERAGE-ATOM MODEL

Le Journal de Physique Colloques ◽

10.1051/jphyscol:1988142 ◽

1988 ◽

Vol 49 (C1) ◽

pp. C1-215-C1-215

Author(s):

R. M. MORE ◽

G. B. ZIMMERMAN ◽

Z. ZINAMON

Keyword(s):

Dielectronic Recombination ◽

Atom Model ◽

Average Atom Model

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EXPERIMENTS ON ELECTRON IMPACT EXCITATION AND DIELECTRONIC RECOMBINATION AT HARVARD-SMITHSONIAN

Le Journal de Physique Colloques ◽

10.1051/jphyscol:1989148 ◽

1989 ◽

Vol 50 (C1) ◽

pp. C1-405-C1-409

Author(s):

L. D. GARDNER ◽

J. L. KOHL ◽

D. W. SAVIN ◽

A. R. YOUNG

Keyword(s):

Electron Impact ◽

Dielectronic Recombination ◽

Impact Excitation ◽

Electron Impact Excitation

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Material Identification in Presence of Metal for Baggage Screening

Electronic Imaging ◽

10.2352/issn.2470-1173.2020.14.coimg-294 ◽

2020 ◽

Vol 2020 (14) ◽

pp. 294-1-294-8

Author(s):

Sandamali Devadithya ◽

David Castañón

Keyword(s):

Atomic Number ◽

Effective Atomic Number ◽

Simulated Data ◽

Dual Energy ◽

Basis Functions ◽

Total Variation Regularization ◽

Ct Scanner ◽

Edge Preserving ◽

Baggage Screening ◽

Dual Energy Imaging

Dual-energy imaging has emerged as a superior way to recognize materials in X-ray computed tomography. To estimate material properties such as effective atomic number and density, one often generates images in terms of basis functions. This requires decomposition of the dual-energy sinograms into basis sinograms, and subsequently reconstructing the basis images. However, the presence of metal can distort the reconstructed images. In this paper we investigate how photoelectric and Compton basis functions, and synthesized monochromatic basis (SMB) functions behave in the presence of metal and its effect on estimation of effective atomic number and density. Our results indicate that SMB functions, along with edge-preserving total variation regularization, show promise for improved material estimation in the presence of metal. The results are demonstrated using both simulated data as well as data collected from a dualenergy medical CT scanner.

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A Spectrum-Adaptive Decomposition Method for Effective Atomic Number Estimation Using Dual Energy CT

Electronic Imaging ◽

10.2352/issn.2470-1173.2020.14.coimg-293 ◽

2020 ◽

Vol 2020 (14) ◽

pp. 293-1-293-7

Author(s):

Ankit Manerikar ◽

Fangda Li ◽

Avinash C. Kak

Keyword(s):

Atomic Number ◽

Decomposition Method ◽

Traditional Approach ◽

Effective Atomic Number ◽

Dual Energy ◽

Performance Comparison ◽

Estimation Methods ◽

Dual Energy Ct ◽

Projection Data ◽

X Ray

Dual Energy Computed Tomography (DECT) is expected to become a significant tool for voxel-based detection of hazardous materials in airport baggage screening. The traditional approach to DECT imaging involves collecting the projection data using two different X-ray spectra and then decomposing the data thus collected into line integrals of two independent characterizations of the material properties. Typically, one of these characterizations involves the effective atomic number (Zeff) of the materials. However, with the X-ray spectral energies typically used for DECT imaging, the current best-practice approaches for dualenergy decomposition yield Zeff values whose accuracy range is limited to only a subset of the periodic-table elements, more specifically to (Z < 30). Although this estimation can be improved by using a system-independent ρe — Ze (SIRZ) space, the SIRZ transformation does not efficiently model the polychromatic nature of the X-ray spectra typically used in physical CT scanners. In this paper, we present a new decomposition method, AdaSIRZ, that corrects this shortcoming by adapting the SIRZ decomposition to the entire spectrum of an X-ray source. The method reformulates the X-ray attenuation equations as direct functions of (ρe, Ze) and solves for the coefficients using bounded nonlinear least-squares optimization. Performance comparison of AdaSIRZ with other Zeff estimation methods on different sets of real DECT images shows that AdaSIRZ provides a higher output accuracy for Zeff image reconstructions for a wider range of object materials.

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