Correlation effects for positron annihilation with core and semicore electrons

Barbiellini, B.; Puska, Martti J.; Alatalo, M.; Hakala, Mikko; Harju, Ari; Korhonen, T.; Siljamäki, S.; Torsti, T.; Nieminen, Risto M.

doi:10.1016/s0169-4332(96)01070-7

Cited by 6 publications

(7 citation statements)

References 20 publications

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“…In order to achieve quantitative agreement with the experiments in the low-momentum region, one should perform a self-consistent band calculation for the valence electrons. [12][13][14] This is, of course, computationally much more demanding, which limits the use of such methods to cases where an accurate calculation for one or very few different systems is needed. In order to obtain trends, however, it is preferable to use simpler methods, such as the present one.…”

Section: Methodsmentioning

confidence: 99%

Calculation of the Doppler broadening of the electron-positron annihilation radiation in defect-free bulk materials

et al. 2000

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Results of a calculation of the Doppler broadening of the positron-electron annihilation radiation and positron lifetimes in a large number of elemental defect-free materials are presented. A simple scheme based on the method of superimposed atoms is used for these calculations. Calculated values of the Doppler broadening are compared with experimental data for a number of elemental materials, and qualitative agreement is obtained. These results provide a database which can be used for characterizing materials and identifying impurityvacancy complexes.

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Section: Methodsmentioning

confidence: 99%

Calculation of the Doppler broadening of the electron-positron annihilation radiation in defect-free bulk materials

et al. 2000

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“…These factors quantify the enhancement that results from the non-local corrections to the annihilation vertex. Such factors are common in positron-atom, positronium [11,80], positron-charged-ion [45,81] and positroncondensed-matter studies [2,15,26,29,30,33,34,82,83]. They are, however, usually calculated in some phenomenological way.…”

Section: B Vertex Enhancement Factors For Annihilation γ-Spectramentioning

confidence: 99%

“…These are often computed using the independent-particle approximation (IPA) [12,24], or in a modified IPA framework that includes phenomenological enhancement factors that attempt to account for the important effects of electronpositron correlations [15,16,20,23,[25][26][27][28][29]. In most cases, the materials of interest are condensed matter systems, and the enhancement factors are usually calculated using a variety of density functional theory methods, e.g., the local density approximation (LDA) [2,30], the generalized gradient approximation (GGA) [31][32][33][34], or the weighted density approximation (WDA) [35][36][37], all of which rely heavily on theoretical considerations of the electron gas. However, due to the strong variations in the density, the LDA is not expected to work well for the core electrons, and has been found to overestimate the annihilation rates [37] The enhancement factor approach within the one-component and Boroński-Nieminen twocomponent LDA [30], as well as within the GGA, have been tested and compared with bound positron-atom stochastic variational calculations in Ref.…”

Section: Introductionmentioning

confidence: 99%

Positron annihilation with core and valence electrons

Green,

Gribakin

2015

Preprint

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γ-ray spectra for positron annihilation with the core and valence electrons of the noble gas atoms Ar, Kr and Xe is calculated within the framework of diagrammatic many-body theory. The effect of positron-atom and short-range positron-electron correlations on the annihilation process is examined in detail. Short-range correlations, which are described through non-local corrections to the vertex of the annihilation amplitude, are found to significantly enhance the spectra for annihilation on the core orbitals. For Ar, Kr and Xe, the core contributions to the annihilation rate are found to be 0.55%, 1.5% and 2.2% respectively, their small values reflecting the difficulty for the positron to probe distances close to the nucleus. Importantly however, the core subshells have a broad momentum distribution and markedly contribute to the annihilation spectra at Doppler energy shifts > ∼ 3 keV, and even dominate the spectra of Kr and Xe at shifts > ∼ 5 keV. Their inclusion brings the theoretical spectra into excellent agreement with the experimental γ-spectra across the full range of Doppler energy shifts. Additionally, the theory enables the calculation of the 'exact' vertex enhancement factors γn for individual core and valence subshells n . They are found to follow a simple and physically motivated scaling with the subshell ionization energy I n : γn = 1 + A/I n + (B/I n ) β , where A, B and β are positive constants. It is demonstrated that these factors can be incorporated in simple independent-particle-model calculations to successfully reconstruct the true many-body annihilation γ-spectra. This formula can be used to determine the enhancement factors for positron annihilation with core electrons of atoms across the periodic table, and with the localized atomic-like core electrons of condensed matter systems.

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“…Recently the promising problem of analyzing the positron annihilation with core electrons has been attacked both experimentally and theoretically [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The chemical selectivity of the positron probe can be used to detect impurity atoms associated to open volume defects.…”

Section: Introductionmentioning

confidence: 99%

Doppler-broadening measurements of positron annihilation with high-momentum electrons in pure elements

Brusa

Deng

Karwasz

et al. 2002

Nuclear Instruments and Methods in Physics Research Section B:

101

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Doppler-broadening measurements of the electron-positron annihilation line in twenty-seven single-element samples are presented. A coincidence technique has been used to suppress the background and to evidence the contribution of positron annihilation with core electrons. Systematic dependences on the atomic number of the target material are found in ratio curves obtained dividing the measured spectra by the spectrum of a reference material. The positron lifetime technique has been used to detect the presence of positron traps in all the samples. The change in the highmomentum part of the annihilation line due to positron trapping is illustrated. The measured data are in a good qualitative agreement with recent theoretical calculation and constitute the most complete measurement series, up to now, to establish a future data-base for positron annihilation spectroscopy.

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Correlation effects for positron annihilation with core and semicore electrons

Cited by 6 publications

References 20 publications

Calculation of the Doppler broadening of the electron-positron annihilation radiation in defect-free bulk materials

Calculation of the Doppler broadening of the electron-positron annihilation radiation in defect-free bulk materials

Positron annihilation with core and valence electrons

Doppler-broadening measurements of positron annihilation with high-momentum electrons in pure elements

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