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Wyświetlanie 1-15 z 67
Tytuł:
Free Volume in Plastified Poly(Vinyl Chlorate)
Autorzy:
Borek, J.
Osoba, W.
Powiązania:
https://bibliotekanauki.pl/articles/1933477.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Positron lifetimes measurements in pure poly(vinyl chlorate) (PVC) and in plastified PVC were performed. Three different plasticizers were used: dibutyl phtalate, dioctyl phtalate and tricresyl phosphate. The measured samples were prepared of PVC with two different plasticizers concentration (20% and 30% of the plasticizers in the poly(vinyl chlorate)). All the measurements were performed in air at room temperature. A conventional fast-slow coincidence lifetime spectrometer was used for the measurements. Free volume radii were calculated from the lifetime data.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 91-95
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Quasi-Positronium in Polyethylene Terephthalate - Temperature and Magnetic Quenching Effects
Autorzy:
Consolati, G.
Quasso, F.
Powiązania:
https://bibliotekanauki.pl/articles/1928970.pdf
Data publikacji:
1993-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
The features of the positron-electron bound system (quasi-positronium, qPs) in the semicrystalline polymer polyethylene terephthalate (mylar) are obtained while studying the dependence of the ortho-qPs lifetime on temperature in the range of 25-105°C, in the presence as well as in the absence of magnetic fields. In particular, the "anomalous" effect, previously discovered by Bisi et al. at room temperature, is maintained at higher temperature.
Źródło:
Acta Physica Polonica A; 1993, 83, 3; 273-276
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Effective Electron-Positron Potential in Jellium
Autorzy:
Stachowiak, H.
Boroński, E.
Lach, J.
Powiązania:
https://bibliotekanauki.pl/articles/1929114.pdf
Data publikacji:
1993-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.60.+z
Opis:
One of the methods of determining theoretical annihilation characteristics in real metals is the approximation called Bloch modified ladder approach. In this approach a Bethe-Goldstone type equation is solved with an effective electron-positron potential obtained previously for jellium of the corresponding electron density. If one wishes to include the dependence on the local electron density of the e$\text{}^{+}$-e$\text{}^{-}$ effective potential in this formalism, it is necessary to know this potential for jellium, for metallic and above metallic densities. A review of different proposed e$\text{}^{+}$-e$\text{}^{-}$ potentials is presented and their correctness is evaluated from the point of view of their application in a Bethe-Goldstone type formalism which is the jellium analogue of Bloch modified ladder approach.
Źródło:
Acta Physica Polonica A; 1993, 83, 3; 391-394
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Systematic Measurements of Doppler-Coincidence Spectra for Positron Annihilation in Pure Metals and Semiconductors
Autorzy:
Deng, W.
Pliszka, D.
Brusa, R. S.
Karwasz, G. P.
Zecca, A.
Powiązania:
https://bibliotekanauki.pl/articles/2030758.pdf
Data publikacji:
2002-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Doppler-broadening measurements of the electron-positron annihilation line in twenty six elements are presented. The adopted coincidence technique allows to reduce the background and point out the contribution of positron annihilation with core electrons. The changes of the high momentum contribution is presented for selected examples and a semiempirical analysis of the dependence on electronic structure is performed. Measured data are in a good agreement with recent theoretical calculations and can be used to identification of impurities surrounding open volume defects.
Źródło:
Acta Physica Polonica A; 2002, 101, 6; 875-892
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Investigation of the Free Volume Changes in Thermally Treated Polyethylene by Positron Annihilation
Autorzy:
Osoba, W.
Powiązania:
https://bibliotekanauki.pl/articles/2008147.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Positron lifetimes measurements in polyethylene were performed. Samples of the polyethylene were heated in the temperature range from 320 to 570 K. After cooling, the samples were used for the lifetime measurements in air at room temperature. A conventional fast-slow coincidence lifetime spectrometer was used for the measurements. Mean free volumes radii were calculated from the lifetime data.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 632-636
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Screening of a Positron in An Inhomogeneous Electron Gas
Autorzy:
Stachowiak, H.
Powiązania:
https://bibliotekanauki.pl/articles/2008186.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.60.+z
Opis:
Calculations of the local annihilation rate of positrons in inhomogeneous media have been recently performed. However, the problem was solved only for the positron at the center of the inhomogeneity. This allowed to benefit of the spherical symmetry of the problem. Since the positron is usually an itinerant particle, it is necessary in practical applications to perform computations for every possible coordinates of this particle. In the present work local annihilation rates were obtained for noncentral coordinates of the positron.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 663-670
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Enhancement Factors for Electrons in Solids for Some Simple Cases
Autorzy:
Stachowiak, H.
Boroński, E.
Banach, G.
Powiązania:
https://bibliotekanauki.pl/articles/2025066.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
The approach to e$\text{}^{+}$-e$\text{}^{-}$ interaction in jellium proposed by Gondzik and Stachowiak proved to be simple numerically and leading to reasonable results. This is why it seemed to be particularly suited for generalizations to real solids, a problem that in spite of more than thirty years of research in this direction did not get yet a satisfactory solution. An obstacle up to now was the necessity to solve integro-differential equations in two dimensions. After overcoming this difficulty we were able to compute e$\text{}^{+}$-e$\text{}^{-}$ enhancement for core and valence electrons in lithium and for core electrons in other two-electron core elements. Properties of the electronic cloud screening the positron are investigated for different coordinates of this particle. The results are compared to such simplifying guesses concerning this problem as the local density, the generalized gradient and the weighted density approximations.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 503-513
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Surfaces of Electron-Emitting Glasses Studied by a Slow Positron Beam
Autorzy:
Pliszka, D.
Gazda, M.
Kusz, B.
Trzebiatowski, K.
Karwasz, G. P.
Deng, W.
Brusa, R. S.
Zecca, A.
Powiązania:
https://bibliotekanauki.pl/articles/2025748.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Semi-conducting glasses used for electron multipliers and microchannel plate devices are obtained by surface modification of Pb or Bi-reach silicon-based glasses. The reduced layer extends down to 200-500 nm, much more than the effective depth of the electron-emitting layer. By the use of slow-positron beam we monitor the structural changes undergoing in near-to-surface layers after isothermal annealing. The measurements suggest a possible correlation between secondary-electron emission coefficient and the Doppler-broadening S-parameter. On these samples there were also performed atomic force microscopy, secondary electron emission, differential scanning calorimetry, and electric conductivity measurements.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 465-472
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Defect Study on Deformed Fe-Si Alloys by Positron Annihilation Techniques
Autorzy:
Chou, K. W.
De Baerdemaeker, J.
Peral, V.
Ruiz, D.
Houbaert, Y.
Segers, D.
Powiązania:
https://bibliotekanauki.pl/articles/2043321.pdf
Data publikacji:
2005-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
A set of Fe-Si samples with different Si content, varying from 0 to 7.6 wt.%, was investigated using positron annihilation spectroscopy. Different deformations were performed on these samples and the lineshape parameters of the annihilation line were measured in order to investigate the defects in the alloys. An exponential decay of the S-parameter in function of the time can be observed after deformation of the samples. The decay constant increases with increasing Si content. During the measurements of the samples with increasing Si content, the initiation of DO$\text{}_{3}$ structure can be seen above 5 wt.% of Si, as well as the decoration by impurities.
Źródło:
Acta Physica Polonica A; 2005, 107, 5; 799-804
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron-Positron Interaction in Jellium: Modification of the Perturbed Hypernetted-Chain Approach
Autorzy:
Stachowiak, H.
Boroński, E.
Powiązania:
https://bibliotekanauki.pl/articles/1812551.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
The approach of Kahana to the electron-positron interaction in an electron gas contains the superfluous assumption that electron scattering on the positron can occur only to momentum states lying outside the Fermi sphere. The perturbed hypernetted-chain approach avoids that assumption, but self-consistency was achieved only in the Born approximation. In the present work a modification of perturbed hypernetted-chain approach allowed to reach self-consistency also at the Kohn-Sham level, at least for 1 ≤ r_s ≤ 3.5. The electron-positron correlation functions obtained in this way are compared to figures resulting from other approaches.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1523-1532
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of Temperature and Pressure on the Free Volume in Thermo-Shrunken Polyethylene by Positron Annihilation
Autorzy:
Danch, A.
Osoba, W.
Wawryszczuk, J.
Powiązania:
https://bibliotekanauki.pl/articles/1812484.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Positron lifetime measurements were performed as a function of temperature and pressure for thermo-shrunken polyethylene. Mean volume of free volume cavities in the investigated polymer was estimated from the results of the measurements. This mean volume turned out to be the smooth function of temperature (from room temperature to 8.5 K) and high pressure (from 0.1 MPa to about 500 MPa). The effect of trapping of the free electrons produced during positron irradiation was observed at low temperature.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1307-1313
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electroni-Positron Scattering in Real Metals
Autorzy:
Boroński, E.
Daniuk, S.
Stachowiak, H.
Powiązania:
https://bibliotekanauki.pl/articles/1928926.pdf
Data publikacji:
1993-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.60.+z
Opis:
The purpose of the paper is to point at the importance of some detailed studies of electron-positron scattering in real metals using wave functions obtained from band structure calculations. In this work some preliminary investigations of the matrix elements of electron-positron scattering, e.g. the transitions from occupied to non-occupied states close to the Fermi surface are presented. One can observe that for s → s transitions of the positron (s, p are orbital quantum numbers) electrons do not change their orbital quantum numbers but for s → p transitions of the positron, electron quantum numbers change by unity.
Źródło:
Acta Physica Polonica A; 1993, 83, 3; 255-260
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Calculations of Annihilation Rate of o-Ps in Pick-Off Process
Autorzy:
Dryzek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2008037.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.60.+z
Opis:
In the paper we suggest the procedure of calculation of the o -Ps lifetime in the pick-off process. The procedure follows the scheme proposed by Tao but we employed the correct positron wave function. We extended our calculations for the case when the o-Ps is overlapping the core region of hydrogen and carbon atoms. The obtained dependence between the lifetime and the radius of the o-Ps fits much better to the experimental one observed in silica gel than the original Tao relation.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 527-532
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Preferential Positron Annihilation in Binary Alloys
Autorzy:
Kuriplach, J.
Dryzek, E.
Dryzek, J.
Šob, M.
Powiązania:
https://bibliotekanauki.pl/articles/2008109.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
71.60.+z
Opis:
The effect of preferential positron annihilation at individual constituent atoms in binary alloys is examined theoretically and experimentally. In particular, the results of recently studied alloys Fe-Al and Mg-Cd together with new preliminary results for the Sn-In system are discussed and summarised. In the case of the Sn-In system, the concentration dependencies of positron annihilation rates and Doppler broadening spectra are analysed.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 605-611
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
To the Measurements of 3γ/2γ Ratio for Positron Annihilation in Matter Using Annihilation Energy Spectrum
Autorzy:
Andrukhovich, S. K.
Berestov, A. V.
Antovich, N. M.
Metelitsa, O. N.
Powiązania:
https://bibliotekanauki.pl/articles/2024055.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.60.+z
78.70.Bj
Opis:
Processes of the summation of cascadeγ-quanta usually neglected, when registering the annihilation energy spectrum for the determination of the three-photon annihilation probability P$\text{}_{3γ}$ of positronium in samples, are studied. The deviations of the actual P$\text{}_{3γ}$ value from that determined without allowance made for the summation processes are 56% and 25% for NaI(Tl) and Ge detectors placed at the distance of 3 cm from a positron source, respectively.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 315-320
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 67

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