Volume correction factor in electron-Indium atom scattering experiments

In crossed electron beam - Indium atom beam scattering experiments the measured signal arises from a spatial region (the 'interaction volume') defined by the overlap of the electron and target atom beam and the view cone of the detector. The exchange of the interaction volume with the scattering angle, named a volume correction factor is discussed. The approach of R. T. Brinkmann and S. Trajmar (J. Phys. E 14, 245-254 (1981)) is adopted for our experimental conditions to determine the volume correction factor and accordingly to transfer angular distributions of scattered electrons to relative differential cross sections.

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Positronium–atom scattering

Canadian Journal of Physics ◽

10.1139/p96-062 ◽

1996 ◽

Vol 74 (7-8) ◽

pp. 434-444 ◽

Cited By ~ 74

Author(s):

Mary T. McAlinden ◽

F. G. R. S. MacDonald ◽

H. R. J. Walters

Keyword(s):

Cross Sections ◽

Born Approximation ◽

Atomic Hydrogen ◽

Argon Atom ◽

Target Atom ◽

Inelastic Collisions ◽

Final States ◽

Initial State ◽

Total Cross Sections ◽

Atom Scattering

Calculations of total cross sections for Ps(1 s) scattering by atomic hydrogen, helium, and argon are reported for the energy range 0–150 eV. The results for atomic hydrogen have been evaluated exactly within the first Born approximation. For collisions with helium and argon in which the target remains in its initial state (so called target elastic collisions) it is assumed that the positronium scatters off a frozen target atom and a coupled positronium pseudostate approximation is then used to calculate the cross sections. For collisions in which the target atom is excited or ionized (target inelastic collisions) the first Born approximation is adopted. Here there is a significant problem in summing over all final states of the target and for this a scheme due to Hartley and Walters has been employed. It is found that for the light targets, hydrogen and helium, target inelastic collisions become dominant above 45 and 105 eV, respectively, while for the heavier argon atom, target elastic scattering is always more important. Except at the lowest energies, and for both target elastic and target inelastic collisions, positronium ionization is the main outcome of the collision for all three atoms. There is an encouraging degree of agreement at the higher energies with the total cross-section measurements of Zafar et al. and Laricchia et al. for helium and argon. The present approximations do not include electron exchange between the positronium and the atom which may be the main source of disagreement between theory and experiment elsewhere.

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High-resolution topographic SEM and radiation damage: The rationale for using low beam voltage

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100131024 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1278-1279

Author(s):

James Pawley ◽

David Joy

Keyword(s):

High Resolution ◽

Imaging Techniques ◽

Morphological Structure ◽

Radiation Sensitivity ◽

Beam Specimen ◽

Measured Signal ◽

Practical Consideration ◽

Interaction Volume ◽

Impact Area ◽

Signal Contrast

The scanning electron microscope (SEM) builds up an image by sampling contiguous sub-volumes near the surface of the specimen. A fine electron beam selectively excites each sub-volume and then the intensity of some resulting signal is measured and then plotted as a corresponding intensity in an image. The spatial resolution of such an image is limited by at least three factors. Two of these determine the size of the interaction volume: the size of the electron probe and the extent to which detectable signal is excited from locations remote from the beam impact area. A third limitation emerges from the fact that the probing beam is composed of a number of discrete particles and therefore that the accuracy with which any detectable signal can be measured is limited by Poisson statistics applied to this number (or to the number of events actually detected if this is smaller). As in all imaging techniques, the limiting signal contrast required to recognize a morphological structure is constrained by this statistical consideration. The only way to overcome this limit is to increase either the contrast of the measured signal or the number of beam/specimen interactions detected. Unfortunately, these interactions deposit ionizing radiation that may damage the very structure under investigation. As a result, any practical consideration of the high resolution performance of the SEM must consider not only the size of the interaction volume but also the contrast available from the signal producing the image and the radiation sensitivity of the specimen.

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Some comments on positron–atom scattering at intermediate energy

Canadian Journal of Physics ◽

10.1139/p82-072 ◽

1982 ◽

Vol 60 (4) ◽

pp. 558-564 ◽

Cited By ~ 1

Author(s):

F. W. Byron Jr.

Keyword(s):

Finite Number ◽

Cross Sections ◽

Infinite Number ◽

Intermediate Energy ◽

Total Cross Sections ◽

Type Approximation ◽

Atom Scattering ◽

Target States

A brief survey of available theoretical techniques is given for positron–atom scattering. The distinction between methods involving a finite number of target states and those with an infinite number of target states is emphasized. The situation regarding total cross sections is summarized, and a new, non-perturbative, eikonal-type approximation, based on the work of Wallace, is introduced.

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Phenotypic plasticity in leaves of four species of arctic Festuca (Poaceae)

Canadian Journal of Botany ◽

10.1139/b95-192 ◽

1995 ◽

Vol 73 (11) ◽

pp. 1810-1823 ◽

Cited By ~ 14

Author(s):

Nicole S. Ramesar-Fortner ◽

Nancy G. Dengler ◽

Susan G. Aiken

Keyword(s):

Phenotypic Plasticity ◽

Cross Sections ◽

Leaf Blade ◽

Growth Traits ◽

Continuous Light ◽

Taxonomic Status ◽

Trichome Density ◽

Experimental Conditions ◽

University Of Toronto ◽

Species Specific

Leaf phenotypic plasticity of 12 morphological, anatomical, and growth traits was investigated using four species of arctic Festuca (F. baffinensis, F. brachyphylla, F. edlundiae, and F. hyperborea). Plants collected around 78°N in the Canadian Arctic Archipelago were grown for 10 weeks at the University of Toronto in growth chambers in continuous light, under four regimes of temperature and moisture. Significant differences were found between leaves at the time of field collection and leaves of the same plant at the end of the experiment in (i) leaf blade length, (ii) surface vestiture, both in trichome density and angle of the trichomes to the blade surface, and (iii) characters seen in leaf cross sections: blade width, rib thickness, and inter-rib thickness. The four species responded similarly to the experimental conditions, indicating that most of these changes represent part of the developmentally inevitable component of plasticity rather than species-specific adaptations. Trichome density was the only characteristic for which species showed different patterns of response, with a unique pattern of response in F. edlundiae. This and certain growth traits support the taxonomic status of this newly recognized species. The significant effects of temperature and to a lesser degree, water treatments on these leaf anatomical traits indicate that they should be used with caution for the purposes of taxonomy and identification. Key words: Festuca, leaf blade anatomy, phenotypic plasticity.

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Über das Dissoziationsgleichgewicht realer Gase

Zeitschrift für Naturforschung A ◽

10.1515/zna-1966-0310 ◽

1966 ◽

Vol 21 (3) ◽

pp. 252-255

Author(s):

H. Koppe ◽

G. Spies

Keyword(s):

Cross Sections ◽

Bound States ◽

Exact Expression ◽

Mass Action ◽

Quantum Mechanical ◽

Law Of Mass Action ◽

Vibrational States ◽

Degree Of Dissociation ◽

Atom Scattering ◽

Collision Approximation

The quantum mechanical cluster expansion, when applied to the partition function of a gas consisting of atoms whose bound states are the rotational and vibrational states of diatomic molecules, provides an exact expression for the degree of dissociation. The approximation containing only the second cluster integral is shown to be identical with the law of mass action involving the binary collision approximation for the activity coefficient of the dissociated constituent. This coefficient can be calculated from the phase shifts and thus from the cross sections of the elastic atom-atom-scattering.

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Intraluminal three-dimensional optical coherence tomography – a tool for imaging of the Eustachian tube?

The Journal of Laryngology & Otology ◽

10.1017/s002221511800230x ◽

2019 ◽

Vol 133 (2) ◽

pp. 87-94 ◽

Cited By ~ 1

Author(s):

R Schuon ◽

B Mrevlje ◽

B Vollmar ◽

T Lenarz ◽

G Paasche

Keyword(s):

Optical Coherence Tomography ◽

Eustachian Tube ◽

Cross Sections ◽

Ex Vivo ◽

Three Dimensional ◽

Diagnostic Value ◽

Optical Coherence ◽

Experimental Conditions ◽

Non Invasive ◽

Tube Dysfunction

AbstractObjectivesThe cause of Eustachian tube dysfunction often remains unclear. Therefore, this study aimed to examine the feasibility and possible diagnostic use of optical coherence tomography in the Eustachian tube ex vivo.MethodsTwo female blackface sheep cadaver heads were examined bilaterally. Three conditions of the Eustachian tube were investigated: closed (resting position), actively opened and stented. The findings were compared (and correlated) with segmented histological cross-sections.ResultsIntraluminal placement of the Eustachian tube with the optical coherence tomography catheter was performed without difficulty. Regarding the limited infiltration depth of optical coherence tomography, tissues can be differentiated. The localisation of the stent was accurate as was the lumen.ConclusionThe application of optical coherence tomography in the Eustachian tube under these experimental conditions is considered to be a feasible, rapid and non-invasive diagnostic method, with possible diagnostic value for determining the luminal shape and superficial lining tissue of the Eustachian tube.

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Helium Atom Scattering from Cyclopentane, Pyrrolidine and Tetrahydrofurane in Crossed Molecular Beams

Zeitschrift für Naturforschung A ◽

10.1515/zna-1997-0509 ◽

1997 ◽

Vol 52 (5) ◽

pp. 425-431

Author(s):

Christian Gebauer ◽

Olaf Klein ◽

Ralf Schmidt ◽

Wolfhart Seidel

Keyword(s):

High Resolution ◽

Helium Atom ◽

Cross Sections ◽

Differential Cross ◽

Molecular Beam ◽

Molecular Beams ◽

Geometric Transformation ◽

Helium Atom Scattering ◽

Helium Atoms ◽

Atom Scattering

Abstract Scattering of helium atoms by cyclopentane, pyrrolidine and tetrahydrofurane molecules was ob-served in crossed molecular beam experiments. The intensity of scattered helium atoms, depending on the scattering angle, was measured with high resolution, and the damping of the diffraction oscillations of the differential cross sections was used to extract elastic anisotropic interaction potentials for these molecules. The evaluation included a geometric transformation concerning the puckered states of the envelope and the twisted conformation of the molecules. The potentials were found to be rather similar.

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Close Coupling Theory of Positron Scattering from Alkali Atoms

Australian Journal of Physics ◽

10.1071/ph940721 ◽

1994 ◽

Vol 47 (6) ◽

pp. 721 ◽

Cited By ~ 22

Author(s):

Jim Mitroy ◽

Kurunathan Ratnavelu

Keyword(s):

Cross Sections ◽

Alkali Atom ◽

Coupling Theory ◽

Positron Scattering ◽

Close Coupling ◽

Total Cross Sections ◽

Hartree Fock ◽

Atom Scattering ◽

Alkali Atoms ◽

Rearrangement Process

The close coupling equatious for positron-alkali atom scattering are written as a set of coupled momentum-space Lippmann-Schwinger equations. The alkali atom is represented by a frozen-core model based upon the Hartree-Fock approximation. The interaction between the positronium and the residual ion is modified by the inclusion of a core potential. Similarly, a core term is present in the interaction describing the rearrangement process. Close coupling calculations of positron scattering from sodium are performed in a model containing multiple sodium (3s, 3p, 4s, 3d, 4p) and positronium (Is, 2s, 2p) states. Cross sections are reported for an energy range from threshold to 50�eV; the total cross sections are in agreement with experimental data.

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