Atomic processes and radiation transport in stars

1988 ◽  
Author(s):  
Dimitri Mihalas
Keyword(s):  
Radiation Transport ◽  
Atomic Processes

scholarly journals Non-LTE radiation transport in moderate-density plasmas

1990 ◽  
Vol 8 (4) ◽  
pp. 729-740 ◽  
Author(s):  
J. J. MacFarlane ◽  
P. Wang ◽  
G. A. Moses
Keyword(s):  
Transport Model ◽  
Radiation Transport ◽  
Atomic Data ◽  
Rate Equations ◽  
Target Chamber ◽  
Atomic Processes ◽  
Escape Probability ◽  
Line Radiation ◽  
Radiation Diffusion ◽  
Hartree Fock

We present results from non-LTE line radiation transport calculations for high-temperature, optically thick plasmas with densities ∼1016-1020 ions/cm3. The calculations are based on an escape probability radiative transport model in which the atomic rate equations are solved self-consistently with the radiation field. Steady-state ionization and excitation populations are determined by detailed balancing of atomic processes, with photoexcitation effects included. Atomic data are computed using a combination of Hartree-Fock, semiclassical impact-parameter, and distorted-wave calculations. Our results indicate that the reabsorption of line radiation significantly alters the level populations and reduces the radiation flux from several types of fusion-related plasmas. We also compare our results with those obtained from multigroup radiation diffusion calculations, and discuss the ramifications of our results for ICF target chamber plasmas.

In situ REM imaging of surface processes on ceramic bulk crystals from 300 to 1670 K in a conventional TEM

1991 ◽  
Vol 49 ◽  
pp. 660-661
Author(s):  
Z. L. Wang ◽  
J. Bentley
Keyword(s):  
High Temperatures ◽  
Image Resolution ◽  
Atomic Processes ◽  
Crystal Surfaces ◽  
Beam Radiation ◽  
Surface Areas ◽  
Transmission Electron ◽  
Reflection Electron Microscopy ◽  
Gas Reactions

Studying the behavior of surfaces at high temperatures is of great importance for understanding the properties of ceramics and associated surface-gas reactions. Atomic processes occurring on bulk crystal surfaces at high temperatures can be recorded by reflection electron microscopy (REM) in a conventional transmission electron microscope (TEM) with relatively high resolution, because REM is especially sensitive to atomic-height steps.Improved REM image resolution with a FEG: Cleaved surfaces of a-alumina (012) exhibit atomic flatness with steps of height about 5 Å, determined by reference to a screw (or near screw) dislocation with a presumed Burgers vector of b = (1/3)<012> (see Fig. 1). Steps of heights less than about 0.8 Å can be clearly resolved only with a field emission gun (FEG) (Fig. 2). The small steps are formed by the surface oscillating between the closely packed O and Al stacking layers. The bands of dark contrast (Fig. 2b) are the result of beam radiation damage to surface areas initially terminated with O ions.

Field ion microscope investigations of atomic processes at surfaces

1989 ◽  
Vol 47 ◽  
pp. 228-229
Author(s):  
G. L. Kellogg ◽  
P. R. Schwoebel
Keyword(s):  
Single Crystal ◽  
Crystal Surface ◽  
Linear Chain ◽  
Atom Probe ◽  
Nucleation And Growth ◽  
Single Atom ◽  
Initial Structure ◽  
Atomic Processes ◽  
Single Crystal Surfaces ◽  
Field Ion Microscope

Although no longer unique in its ability to resolve individual single atoms on surfaces, the field ion microscope remains a powerful tool for the quantitative characterization of atomic processes on single-crystal surfaces. Investigations of single-atom surface diffusion, adatom-adatom interactions, surface reconstructions, cluster nucleation and growth, and a variety of surface chemical reactions have provided new insights to the atomic nature of surfaces. Moreover, the ability to determine the chemical identity of selected atoms seen in the field ion microscope image by atom-probe mass spectroscopy has increased or even changed our understanding of solid-state-reaction processes such as ordering, clustering, precipitation and segregation in alloys. This presentation focuses on the operational principles of the field-ion microscope and atom-probe mass spectrometer and some very recent applications of the field ion microscope to the nucleation and growth of metal clusters on metal surfaces.The structure assumed by clusters of atoms on a single-crystal surface yields fundamental information on the adatom-adatom interactions important in crystal growth. It was discovered in previous investigations with the field ion microscope that, contrary to intuition, the initial structure of clusters of Pt, Pd, Ir and Ni atoms on W(110) is a linear chain oriented in the <111> direction of the substrate.

Comparison of Radiation Transport Codes for Solar Particle Events Space Environment: II

2009 ◽  
Author(s):  
Ram Tripathi ◽  
Lawrence Townsend ◽  
Tony Gabriel ◽  
Lawrence PIinsky ◽  
Tony Slaba
Keyword(s):  
Radiation Transport ◽  
Space Environment ◽  
Solar Particle Events ◽  
Solar Particle

A Monte Carlo study of radiation transport through multileaf collimators

2001 ◽  
Vol 28 (12) ◽  
pp. 2497-2506 ◽  
Author(s):  
Jong Oh Kim ◽  
Jeffrey V. Siebers ◽  
Paul J. Keall ◽  
Mark R. Arnfield ◽  
Radhe Mohan
Keyword(s):  
Monte Carlo ◽  
Radiation Transport ◽  
Monte Carlo Study ◽  
Multileaf Collimators

PENGEOM – A general-purpose geometry package for Monte Carlo simulation of radiation transport in complex material structures (New Version Announcement)

2021 ◽  
pp. 107962
Author(s):  
Julio Almansa ◽  
Francesc Salvat-Pujol ◽  
Gloria Díaz-Londoño ◽  
Artur Carnicer ◽  
Antonio M. Lallena ◽  
...  
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Radiation Transport ◽  
General Purpose ◽  
Complex Material
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