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Wyświetlanie 1-10 z 610
Tytuł:
Many-Body Effects Observed in the Positron Annihilation Experiment
Autorzy:
Kontrym-Sznajd, G.
Sormann, H.
Powiązania:
https://bibliotekanauki.pl/articles/2042161.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
78.70.Ck
74.25.Jb
Opis:
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.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 562-569
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Amorphous Bi-Ge-S(Se) Systems Studied by X-Ray Ge K Emission and Absorption Bands
Autorzy:
Drahokoupil, J.
Drbohlav, I.
Polčik, M.
Tichý, L.
Powiązania:
https://bibliotekanauki.pl/articles/1931701.pdf
Data publikacji:
1994-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Dm
Opis:
The X-ray Ge K absorption (emission) bands were measured in the stoichiometric glass system (GeS$\text{}_{2}$)$\text{}_{x}$(Bi$\text{}_{2}$S$\text{}_{3}$)$\text{}_{1-x}$ (x = 0 ÷ 0.5) and in the Ge$\text{}_{20}$Bi$\text{}_{y}$Se$\text{}_{80-y}$ system (y = 0, 7 and 13). The results do not confirm the existence of the Ge-Bi bond and they imply that the GeS$\text{}_{2}$-clusters are formed in both studied systems.
Źródło:
Acta Physica Polonica A; 1994, 86, 5; 721-726
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Formation and Annealing of Micropores in Hematite
Autorzy:
Dauwe, C.
Da Costa, G. M.
Van Hoecke, T.
Segers, D.
Powiązania:
https://bibliotekanauki.pl/articles/1933484.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
In iron oxide powders positrons are trapped in the surface layers and the value of the S-parameter is an indicator of the total specific surface, including external surface and internal surfaces of micropores. The evolution of micropores is followed when α-FeOOH is thermally decomposed into α-Fe$\text{}_{2}$O$\text{}_{3}$. It is shown that the micropore formation is not linked to the decomposition process, but that they also form in hematite synthesized from a ferrihydrite precursor in aqueous solution.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 119-123
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Remarks on Reconstruction of Defects Distribution by Positron Lifetime Measurements
Autorzy:
Dryzek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1933485.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
It is well known that the positron trapping rate obtained from positron lifetime measurements depends upon defect concentrations and trapping efficiency. If a distribution of open volume defects exists, a distribution of trapping efficiency also could be present. As an example, the calculation of trapping efficiency as a function of radius of defects in Al is presented. The correct explanation of defect size distribution obtained by positron lifetime measurements needs to introduce some additional assumptions about trapping efficiency.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 125-128
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Studies of the Cu-Mn System
Autorzy:
Nicht, E.-M.
Brauer, G.
Kajcsos, Zs.
Molnar, B.
Powiązania:
https://bibliotekanauki.pl/articles/1933529.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The superstructures Cu$\text{}_{3}$Mn and Cu$\text{}_{5}$Mn have been characterized for the first time by X-ray and differential scanning calorimetry measurements. In addition, positron lifetime measurements are presented in order to show the defect structure of these alloys. It turned out that the annealing behaviour is equal for the two different alloys and the two different deforming processes. An annealing temperature of 300°C is not sufficient to obtain a defect free state.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 205-210
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Annihilation Studies of the Ni-H Systems Containing Thermally Induced Crystal Lattice Defects
Autorzy:
Pająk, J.
Powiązania:
https://bibliotekanauki.pl/articles/1933538.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The interaction between hydrogen and thermally induced defects has been studied in nickel samples using the positron annihilation technique. From measurements further evidence has been found for agglomeration of vacancies and small vacancy complexes into large-size three-dimensional void-like defects in the plastically deformed and electron beam irradiated samples containing hydrogen.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 219-223
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
X-Ray Absorption Near Edge Structure Analysis of HgMnSe, HgFeSe and HgTeSe
Autorzy:
Burattini, E.
Kisiel, A.
Markowski, R.
Dalba, G.
Giriat, W.
Powiązania:
https://bibliotekanauki.pl/articles/1924330.pdf
Data publikacji:
1993-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Dm
Opis:
Experimental studies of the Se K X-ray absorption edges have been carried out in HgTe$\text{}_{0.5}$Se$\text{}_{0.5}$, Hg$\text{}_{0.8}$Mn$\text{}_{0.2}$Se and Hg$\text{}_{0.9}$Fe$\text{}_{0.1}$Se. A comparison is made for Hg$\text{}_{0.5}$Mn$\text{}_{0.5}$Se and Hg$\text{}_{0.5}$Fe$\text{}_{0.5}$Se theoretical results obtained by the self-consistent, semi-relativistic LMTO method within the LD approximation. Small differences of Se K edge XANES have been shown for HgTeSe and HgSe in contrary to evident differences for HgMnSe and HgFeSe. This behaviour of the absorption Se K edges is related to significant, hybridized contribution of the 3d and 4s Mn or Fe unoccupied states. The maximal contributions of the hybridized bands of the hypothetic zinc-blende MnSe or FeSe were estimated using the virtual crystal model. These maximal contributions are situated at about 6 eV and 17 eV in zinc-blende MnSe and at -0.8 eV and 5.5 eV in zinc-blende FeSe. For HgFeSe apart from the evidence of the strongly localized resonant donor (empty for low Fe concentrations) the complementary hybridized contribution of Fe 3d empty states also situated around the conduction band minimum should be taken into consideration.
Źródło:
Acta Physica Polonica A; 1993, 83, 1; 107-114
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Kinetics of the Spin-Conversion of Positronium Measured by β$\text{}^{+}$γ∆E Age-Momentum Correlation
Autorzy:
Lauff, U.
Maier, K.
Major, J.
Seeger, A.
Stoll, H.
Wesołowski, P.
Koch, M.
Bilard, I.
Abbé, J.
Duplâtre, G.
Powiązania:
https://bibliotekanauki.pl/articles/1929104.pdf
Data publikacji:
1993-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
Age-momentum correlation (AMOC) measurements provide time-resolved information on the momentum distribution of annihilating electron-positron pairs through correlated determination of Doppler broadening (∆E) of the 511 keV annihilation radiation line and positron age. In the β$\text{}^{+}$γ∆E AMOC technique implemented at the Stuttgart pelletron accelerator the start signals for the age measurements are generated when the relativistic positrons pass through a fast plastic scintillator, which has a detection efficiency close to unity. Beam-based β$\text{}^{+}$γ∆E AMOC measurements thus combine high β$\text{}^{+}$γ∆E triple-coincidence rates with low background. From a practical point of view this constitutes a major progress compared to conventional (source-based) γγ∆E AMOC measurements. The AMOC technique permits direct access to a wide variety of time-dependent processes, among them the reaction kinetics in positronium chemistry. As an example, we present a β$\text{}^{+}$γ∆E AMOC investigation of the kinetics of a spin-conversion reaction of positronium in methanol induced by the presence of a nitrosyl free-radical paramagnetic solute (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl , HTEMPO). The AMOC measurements allowed the time-resolved observation of the spin-conversion process, which had been investigated before by uncorrelated positron lifetime and Doppler-broadening measurements. It is found that within the concentration range investigated (≤ 0.1 mol/l) the spin-conversion reaction rate at room temperature depends linearly on the HTEMPO concentration with a reaction-rate constant k$\text{}_{conv}$ = (22.5 ± 0.5) × 10$\text{}^{9}$ l mol$\text{}^{-1}$ s$\text{}^{-1}$.
Źródło:
Acta Physica Polonica A; 1993, 83, 3; 349-358
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Use of Energy Summing for Selection of Coincidence Events in Positron-Lifetime Spectroscopy
Autorzy:
Bec̆vár̆, F.
C̆iz̆ek, J.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/2007883.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
A BaF$\text{}_{2}$ positron-lifetime spectrometer equipped with a coincidence system that represents a compromise between the traditional fast-fast and fast-slow arrangements is described. The main difference of the present configuration from both the fast-slow and fast-fast ones consists in use of a sum of the energy signals from the start and stop detectors to select the coincidence events. Quality of the spectrometer response function (≈ 150 ps FWHM for $\text{}^{22}$Na) is very close to that observed for our fast-slow configuration with the equivalent detectors but throughput of the present apparatus is increased almost by a factor of two. Moreover, the electronic scheme becomes less complicated, which has also a positive impact on its cost.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 448-454
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium in Small and Large Voids in Vycor Glass
Autorzy:
Ciesielski, K.
Dawidowicz, A. L.
Goworek, T.
Powiązania:
https://bibliotekanauki.pl/articles/2007951.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The intensities of ortho-positronium components related to the pores and to small voids in the bulk were determined for a series of Vycor glasses. The ratio of "pore fraction" to the total o-Ps yield depends on the specific surface area of the porous medium. The diffusion coefficient for o-Ps was found equal to 3.7×10$\text{}^{-5}$ cm$\text{}^{2}$/s.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 483-486
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-10 z 610

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