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1
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Compton Scattering and Various ACAR Experiments in~Mg

100%
Kontrym-Sznajd G.
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vol. 125
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issue 3
696-699
EN
Electron-positron (e-p) momentum densities in Mg are studied using three different sets of angular correlation of annihilation radiation (ACAR) and Compton scattering experimental data. ACAR data, measured with almost identical resolution, give both a similar anisotropy of the Fermi surface and a similar e-p enhancement factor inside this surface. However, as concerns a contribution of Umklapp components of valence-electron densities there are essential differences depending on experimental data. Due to a strong dependence of such densities on different theoretical approaches describing e-p correlations, it is suggested to perform additional, high statistics and resolution ACAR measurements for Mg and analyze them as suggested in the paper.
2
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Consistency and Symmetry Conditions for Plane Projections

100%
Kontrym-Sznajd G.
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vol. 95
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issue 4
581-585
EN
Interdependences between plane projections of densities ρ(p) for various crystallographical structures are derived from the conditions of both the consistency and symmetry of projections. Some additional relations are obtained by treating plane projections as line projections of ρ̃_{L}(p) (ρ̃_{L} is a line projection of ρ(p)) and using the consistency and symmetry conditions for the line projections. The relations found can be utilized for both an improvement of experimental spectra and a verification of various techniques used for e.g. correcting Compton profiles.
3
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Transform Methods of Computerized Tomography in Studying Electronic Structure and Fermi Surfaces of Solids

100%
Kontrym-Sznajd G.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1417-1427
EN
We present mathematical methods of computerized tomography, based on an analytical inversion of the Radon transform either in terms of the Fourier transforms or series of orthogonal polynomials. These techniques, so-called transform methods, are discussed for reconstructing electronic densities from both line and plane projections measured either in the two-dimensional angular correlations of annihilation radiation or in one-dimensional angular correlations of annihilation radiation and the Compton scattering experiments. This paper is devoted to review all of the papers where such techniques were applied for studying electronic momentum densities and the Fermi surface of solids by angular correlations of annihilation radiation and the Compton scattering experiments.
4
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Umklapp Components of the Positron Momentum Density Depending on Different Models for the Positron Wave Function

64%
Kontrym-Sznajd G., Sormann H.
Acta Physica Polonica A
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1995
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vol. 88
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issue 1
185-192
EN
In this paper, we present a numerical investigation about the question how sensitively Fourier coefficients of the positron wave function ψ_{+} react to different (and not too strong) changes of ψ_{+}. In order to obtain general information about this problem, we studied this sensitivity for several bcc and fcc metals and for different models of the positron wave function. Summarizing our results, we can say that this sensitivity is generally small (or at least moderate) for Fourier coefficients belonging to reciprocal lattice vectors G which lie nearest to the centre of the momentum space. For the outer vectors G, the amount of this sensitivity is strongly dependent on the crystal structure of the metal and on the special like of the change of the positron wave function.
5
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Electronic Structure Seen by Positrons in Extended and Reduced Zone Schemes

64%
Kontrym-Sznajd G., Sormann H.
Acta Physica Polonica A
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1995
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vol. 88
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issue 1
177-184
EN
The influence of the positron on the momentum distribution of annihilation quanta is investigated. Basing on general considerations, we show that a noninteracting positron, which generally reduces electronic densities, may enlarge some particular electronic umklapp components. Numerical tests were performed for alkalis, Al, Cu and Pd by applying augmented plane wave band structure calculations. In the paper we discuss also the influence of this effect on the electron-positron densities after including the electron-positron correlation effects.
6
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Densities of Valence Electrons in Simple Metals Effective with Respect to Electron-Positron Correlations

64%
Kontrym-Sznajd G., Rubaszek A.
Acta Physica Polonica A
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1993
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vol. 83
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issue 3
333-337
EN
The influence of the electron-positron interactions on the momentum density of annihilation quanta in real metals is discussed. The role of momentum dependence of two-particle electron-positron correlations is set forth. The effective densities describing electron-positron correlations are presented for valence electrons in simple metals.
7
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Methods of Extracting Electron-Positron Enhancement Factors from Experimental ACAR Data

64%
Kontrym-Sznajd G., Rubaszek A.
Acta Physica Polonica A
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1993
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vol. 83
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issue 3
339-344
EN
Methods of extracting the full shape of the electron-positron momentum density from experimental angular correlation of positron annihilation radiation curves are discussed. The proposed analysis of experimental data allows more reliable verification of the form of electron-positron enhancement factors near the Fermi surface in simple metals.
8
Content available remote

Consistency and Symmetry Conditions for Line Projections

64%
Kontrym-Sznajd G., Jura A.
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vol. 95
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issue 4
586-590
EN
We present some relations between experimental spectra representing line projections of electronic densities in the momentum space. All spectra which are the projections of the same density, must be interdependent. It can be derived from the consistency condition and symmetry of the line projections. The knowledge of these dependences, found in the paper, can be utilised for an improvement of experimental data as e.g. two-dimensional angular correlation of positron annihilation spectra.
9
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Content available

Fermi-Surface Mapping from 2D Positron Annihilation Data

64%
Kontrym-Sznajd G., Samsel-Czekała M.
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EN
We demonstrate which kind of information on the electronic structure one can get from one-dimensional profiles, interpreted in terms of two-dimensional reconstructed densities. The conversion from one-dimensional to two-dimensional is applied to one-dimensional angular correlation of annihilation radiation profiles of divalent hexagonal close packed metals Mg and Cd. On the example of Mg we show that one should be very careful while studying the Fermi surface from electron-positron (e-p) densities folded into the first Brillouin zone.
10
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Content available

Many-Body Effects Observed in the Positron Annihilation Experiment

64%
Kontrym-Sznajd G., Sormann H.
|
EN
This paper is devoted to study many-body effects in the positron annihilation experiment, both electron-positron (e-p) and electron-electron (e-e) correlations. Various theories of the e-p interaction in real solids were used to verify them by comparing theoretical and experimental e-p momentum densities in Cu and Y. We show that the lattice potential has an essential influence on the e-p correlation effects, i.e. their proper description must be done via periodic lattice potential as e.g. in the Bloch modified ladder theory. Moreover, it is not true that the dynamic parts of the direct e-p and e-e interactions cancel each other because e-e correlations are observed not only in the Compton scattering but also in the positron annihilation experiments.
11
Content available remote

Reconstruction of Densities from Compton Profiles with Applying Jacobi Polynomials

51%
Kontrym-Sznajd G., Samsel M., West R.
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vol. 95
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issue 4
591-595
EN
The advent of synchrotron sources has led to an increasing availability of high resolution Compton profiles J(p_{z}) and a consequent renewed interest in the reconstruction of the corresponding full momentum densities ρ(p). We present results of applying a new method in which the radial parts of ρ(p) and the measured profiles are expressed in terms of the Jacobi polynomials. The technique is demonstrated using model projections that correspond to Mg and Gd spectra. Reconstructed densities, being in very good agreement with model ones, are a very good performance of our new reconstruction algorithm.
12
Content available remote

Comparison of Various Reconstruction Techniques for Line Projections

51%
Kontrym-Sznajd G., Samsel-Czekała M., Biasini M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1429-1434
EN
The most effective and popular algorithms to reconstruct the three-dimensional electron-positron momentum density from the measurements of the two-dimensional angular correlation of annihilation radiation are based on the Fourier transform or polynomial expansion. We compare the efficacy of different methods in reconstructing the momentum density of the rare-earth based compounds ErGa_3, CeIn_3 and model profiles, presenting also our new filtering algorithm.
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