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Wyświetlanie 1-15 z 48
Tytuł:
Does Positronium Feel Dynamics of Polymer Chain?
Autorzy:
Krištiak, J.
Šauša, O.
Bandžuch, P.
Zrubcová, J.
Bartoš, J.
Powiązania:
https://bibliotekanauki.pl/articles/2008075.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
83.80.Dr
Opis:
The annihilation experiments on simple elastomers at wide temperature interval of (15-370) K will be described. The results are consistently interpreted using free-volume models of polymer structure. The procedure of deducing some parameters of theory of polymers (e.g. viscosity, Vogel-Fulcher temperature) from the positron annihilation experiments will be shown. A great potential of positron annihilation in the study of amorphous polymers will be emphasized.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 596-604
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Pressure Effects in ortho-Positronium Annihilation
Autorzy:
Goworek, T.
Wawryszczuk, J.
Zaleski, R.
Powiązania:
https://bibliotekanauki.pl/articles/2042179.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
Opis:
A short review of experiments concerning the influence of high pressure on positron annihilation in molecular solids is given. To this kind of experiments belong e.g. pressure inhibition of positronium formation, pressure induced phase transitions, and free volume swelling in the media intercalated by high pressure gas.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 608-614
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Formation in Solid Long-Chain Alkanes
Autorzy:
Zaleski, R.
Wawryszczuk, J.
Goworek, T.
Powiązania:
https://bibliotekanauki.pl/articles/2042188.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
Opis:
This paper represents a fragment of systematic studies on positron annihilation in solid saturated hydrocarbons (alkanes, paraffins) from C$\text{}_{17}$H$\text{}_{36}$ to C$\text{}_{30}$H$\text{}_{62}$. The Tao-Eldrup model and its extensions allow to identify the places in the crystalline structure where positronium is trapped, and estimate respective trap sizes. In the rigid phase I positronium locates mainly in two-dimensional empty spaces between the lamellae of crystal structure. Additional free volumes exist in high temperature phases due to appearance of n-alkane conformers representing a non-planar molecule distortion. The rise of ortho-positronium intensity with the sample irradiation dose, which was seen earlier in polymers, is observed also in n-alkanes. One can find similarities between the ortho-positronium annihilation in crystalline alkanes and polymers, like exponential character of that rise, and the trap bleaching by illumination. It confirms the same origin of the intensity growth, i.e. the accumulation of trapped electrons. Two kinds of electron traps were found. The time constant of electron accumulation in the traps depends on the carbon chain length and varies with temperature in different way for even- and odd-numbered alkanes.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 635-641
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Three-Quantum Annihilation in Porous Vycor Glass
Autorzy:
Jasińska, B.
Wawryszczuk, J.
Zaleski, R.
Powiązania:
https://bibliotekanauki.pl/articles/2043332.pdf
Data publikacji:
2005-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
Opis:
Three methods of determination of 3γ o-Ps decay intensity are compared. The estimate of 3γ fraction obtained from classical lifetime measurements can be distorted due to a higher absorption of theγ quanta from the continuous spectrum of three-quantum decay, compared to two-quantum one.
Źródło:
Acta Physica Polonica A; 2005, 107, 5; 821-825
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Oscillations in Orthopositronium Annihilation in Magnetic Field in SiO$\text{}_{2}$ Powders
Autorzy:
Berestov, A. V.
Talat, A. S.
Baranov, V. V.
Rudak, E. A.
Martsynkevich, B. A.
Powiązania:
https://bibliotekanauki.pl/articles/1933473.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
07.85.+n
36.10.Dr
78.70.Bj
Opis:
The observation method of γ-quantum angular distribution oscillations in positronium annihilation in magnetic field is essentially improved. Oscillation parameters in the experiment are in agreement with theoretical estimations.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 79-82
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Discrete and Continuous Analysis of Positron Lifetime Spectra: a Comparison
Autorzy:
Consolati, G.
Quasso, F.
Powiązania:
https://bibliotekanauki.pl/articles/2007998.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
71.60.+z
78.70.Bj
Opis:
Positron lifetime spectra in poly[1-(trimethylsilyl)]propine membranes were collected at different temperatures and various number of accumulated counts, in order to compare the results from analyses obtained by different decay models: discrete (that is, purely exponential) or continuous (with at least one distribution of lifetimes). Analysis into four discrete components is inadequate, unless a low number of counts (1 to 2 millions) is accumulated. Conversely, deconvolutions which allow the ortho-positronium lifetime to be distributed give satisfactory fits, even at the highest statistics (60 millions). An equivalent good fit in terms of χ$\text{}^{2}$ test is obtained with a five discrete components analysis, from which it is possible to extract information on the first moments (centroid and standard deviation) of ortho -positronium lifetime distribution.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 505-508
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Formation in Organic Liquids
Autorzy:
Karbowski, A.
Fedus, K.
Służewski, K.
Bruzdowska, J.
Karwasz, G.
Powiązania:
https://bibliotekanauki.pl/articles/1030028.pdf
Data publikacji:
2017-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
82.30.Gg
36.10.Dr
Opis:
This paper reports on the results of positron annihilation lifetime measurements of three organic liquids: benzene (C₆H₆), cyclohexane (C₆H₁₂), and methanol (CH₃OH). The lifetime spectra are acquired at different temperatures for non-degassed, degassed, and oxygen-saturated samples, at temperatures between 5°C and 25°C. The spectra are analyzed using a standard three-exponential model. The influence of oxygen on each lifetime and intensity component is discussed.
Źródło:
Acta Physica Polonica A; 2017, 132, 5; 1466-1469
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Formation in Nanostructured Metals
Autorzy:
Čížek, J.
Melikhova, O.
Hruška, P.
Vlček, M.
Anwand, W.
Liedke, M.
Novotný, M.
Bulíř, J.
Powiązania:
https://bibliotekanauki.pl/articles/1033937.pdf
Data publikacji:
2017-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
41.75.Fr
36.10.Dr
Opis:
Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-γ annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measures of 3-γ annihilation contribution calculated from single γ-ray and coincidence Doppler broadening spectra were calculated and compared.
Źródło:
Acta Physica Polonica A; 2017, 132, 5; 1579-1584
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium Formation at Low Temperatures in Polymers and Other Molecular Solids
Autorzy:
Hirade, T.
Powiązania:
https://bibliotekanauki.pl/articles/2042181.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
36.20.Kr
Opis:
Positronium (Ps) formation by weakly localized long-lived electrons (trapped electrons or anions) and positrons at low temperatures successfully explained the Ps formation enhancement at low temperatures observed in polymers and molecular solids. This Ps formation process is different from Ore process and spur process. The phenomena expected by this Ps formation mechanism, such as an effect due to visible light exposure, a density dependence of weakly localized electrons and the delayed Ps formation were successfully observed as the experimental evidence of this Ps formation process. Some possibilities for application of this new Ps formation were also given. One is a new idea for estimation of spin polarity of positrons. Another is the possibility of application to study the local molecular motion by observing the decay of Ps formation intensity.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 615-622
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Revision of the Model of Formation of Radiolytic Products in Aqueous Solutions
Autorzy:
Stepanov, S. V.
Byakov, V. M.
Powiązania:
https://bibliotekanauki.pl/articles/2042192.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
61.80.Fe
36.10.Dr
78.70.Bj
Opis:
Mathematical model of formation of radiolytic products (e$\text{}_{aq}^{-}$, H, OH, H$\text{}_{2}$, H$\text{}_{3}$O$\text{}^{+}$, OH$\text{}^{-}$, Ps) in water is developed. It takes into account (1) reactions between dissolved scavengers of thermalized and hydrated electrons as well as epithermal ones; (2) ambipolar diffusion expansion of the intratrack species; (3) additional channels of Ps and H$\text{}_{2}$ formation due to appearance of weakly trapped electrons. Good agreement is obtained with experimental data on kinetics of accumulation of the products in pure water and their concentration variations in aqueous solutions.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 651-660
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of Coincidence Doppler Broadening Spectroscopy to Hydrocarbons at Different Substance States
Autorzy:
Yu, R.
Suzuki, T.
Ito, Y.
Djourelov, N.
Kondo, K.
Shantarovich, V. P.
Powiązania:
https://bibliotekanauki.pl/articles/2042205.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
82.30.Gg
78.70.Bj
Opis:
Coincidence Doppler broadening spectroscopy was applied to study n-hexane (C$\text{}_{6}$H$\text{}_{14}$), cyclohexane (C$\text{}_{6}$H$\text{}_{12}$) and cyclohexanone (C$\text{}_{6}$H$\text{}_{10}$O), at solid, as well as liquid states. The experiments were performed in parallel with traditional positron annihilation lifetime spectroscopy. Significant positron trapping by oxygen was observed in cyclohexanone; the oxygen effect is stronger in liquid state than in solid one, which can possibly be attributed to positron solvation in polar solution. Coincidence Doppler broadening results for n-hexane and cyclohexane indicate an existence of higher energetic annihilation electrons in Ps-bubble forming liquids than that in solids.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 697-701
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical Solution of a Two-Particle Model of Positronium Confined in Small Cavities
Autorzy:
Tanzi Marlotti, G.
Castelli, F.
Consolati, G.
Powiązania:
https://bibliotekanauki.pl/articles/1033255.pdf
Data publikacji:
2017-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
34.80.Lx
78.70.Bj
Opis:
The positronium atom (Ps) is widely used as a probe to characterize nanoporous and mesoporous materials. Existing theoretical models for describing Ps annihilation rates by pick-off processes generally treat Ps as a point particle confined in a potential well. Hence these models do not justify any change in the internal structure of Ps, which is experimentally accessible by means of the contact density parameter. Recently we formulated a two-particle model in which only the electron is confined in the cavity, while the positron is moving freely and feels the medium via a positive work function. We present here a numerical treatment of the problem of calculating contact densities and pick-off annihilation rates, by using a variational method. Results are in agreement with experimental data for a large class of materials, and suggest a way to connect these data with pore sizes and positron work functions.
Źródło:
Acta Physica Polonica A; 2017, 132, 5; 1575-1578
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A new approach to the presentation of the positron annihilation lifetime spectroscopy results, n-alkanes
Autorzy:
Zgardzińska, B.
Standzikowski, K.
Powiązania:
https://bibliotekanauki.pl/articles/1057935.pdf
Data publikacji:
2017-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
36.10.Dr
78.70.Bj
82.30.Gg
Opis:
The standard form of the positron annihilation lifetime spectroscopy results presentation are two plots of o-Ps lifetime and intensity as a function of external factor, e.g. temperature, pressure. Both o-Ps parameters change (stepwise) when in the medium phase transitions occur. For a more complete picture of the structural changes occurring in the matter we suggest to use an additional plot, in the coordinates, (τ₃, I₃). The hydrocarbons are selected to show the advantages following from the presentation of the results in the intensity-lifetime (INTI) plot.
Źródło:
Acta Physica Polonica A; 2017, 132, 5; 1496-1500
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Investigations of Resorcinol under High Pressure
Autorzy:
Tydda, M.
Jasińska, B.
Powiązania:
https://bibliotekanauki.pl/articles/1196480.pdf
Data publikacji:
2014-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
36.10.Dr
61.66.Hq
Opis:
The investigation of intermolecular free volumes in resorcinol was conducted under high pressure, hydraulic pressure and gas (argon or nitrogen) atmosphere. The sizes of free volumes were estimated basing on the mean lifetime of ortho-positronium (o-Ps). In the first case, a monotonous change of lifetime and intensity was observed for the o-Ps component while the range of pressure was 0-477 MPa. On the other case, the samples were put into the pressure chamber filled with argon or nitrogen in the range of pressure from 0 to 450 MPa. When the pressure chamber was filled with a gas, the appearance of an additional o-Ps component has been found. In the nitrogen atmosphere, the material crushed when the gas pressure reached about 200 MPa, and the mean lifetime of the longest o-Ps component increased.
Źródło:
Acta Physica Polonica A; 2014, 125, 3; 812-815
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Production of Cold Positronium Atoms
Autorzy:
Brusa, R.
Mariazzi, S.
Consolati, G.
Dupasquier, A.
Quasso, F.
Giammarchi, M.
Powiązania:
https://bibliotekanauki.pl/articles/1812479.pdf
Data publikacji:
2008-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
36.10.Dr
36.10.Gv
Opis:
Positronium will play a primary role in the next generation of antimatter experiments through the following antihydrogen production reaction: p̅ + Ps* → p̅e⁺ + e¯. In order to study antimatter physical properties (CPT (charge, parity, time) invariance and principle of equivalence test) it is necessary to keep this system at the lowest possible (sub-kelvin) temperatures. This requires the generation of a suitable flux of cold Ps atoms in a vacuum, a non-trivial requirement at the light of the present experimental results. In this paper we discuss the state of the actual knowledge on positronium formation and consequent emission from metallic surfaces and insulators and we show the opportunity to use suitable porous materials to cool positronium through collisions with the inner walls of the pores. We get a rough indication on the geometrical parameters of the pore and we propose a simple experiment to obtain the kinetic energy - and therefore the equivalent temperature - of emitted positronium without using a positron beam.
Źródło:
Acta Physica Polonica A; 2008, 113, 5; 1301-1306
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 48

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