Temat: DR - Katalog OPAC zbiorów

Skocz do pozycji: 1.

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

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Skocz do pozycji: 2.

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

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Skocz do pozycji: 3.

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

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Skocz do pozycji: 4.

Tytuł:: Positron Porosimetry Studies of Template Removal from As-Synthesized MCM-41 Silica
Autorzy:: Zaleski, R.
Wawryszczuk, J.
Powiązania:: https://bibliotekanauki.pl/articles/1812554.pdf
Data publikacji:: 2008-05
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 78.70.Bj
36.10.Dr
61.43.Gt
81.07.-b
Opis:: The course of template removal from MCM-41 pores was investigated by positron annihilation lifetime spectroscopy. Two methods of removal were the object of interest: a decarbonisation after standard calcination procedure and a novel procedure - pyrolysis in vacuum. The shapes of positron lifetime spectra of decarbonised sample are determined by positronium quenching caused by presence of carbon deposit on the surface. Positron annihilation lifetime spectroscopy allows also monitoring the evolution of empty space inside pores. During pyrolysis no conductive carbon is produced, so consecutive stages of template material transformation are easy to observe. In the case of pyrolysis the effect of pore emptying is obtained at temperature 500 K, lower comparing to calcination and decarbonisation (820 K).
Źródło:: Acta Physica Polonica A; 2008, 113, 5; 1543-1550
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: Controlled Porosity of MCM-41 Obtained by Partial Blocking of Pores by Silicon Oil
Autorzy:: Gorgol, M.
Krasucka, P.
Goworek, J.
Zaleski, R.
Powiązania:: https://bibliotekanauki.pl/articles/1033928.pdf
Data publikacji:: 2017-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 78.70.Bj
36.10.Dr
61.43.Gt
68.43.-h
Opis:: Partial blocking of mesopores in the ordered MCM-41 silica by DC550 silicon oil was proposed as a preparation method of the material with controlled porosity and fixed pore size. The porosity of the samples with various content of DC550 was examined with the use of low temperature nitrogen sorption and positron annihilation lifetime spectroscopy. It was shown that the oil blocks the primary pores by forming the plugs near its entrances, but also partially locates in the interparticle spaces. The comparison of the results obtained from both investigation techniques was used to make the first attempt to obtain the calibration of ortho-positronium intensity, depending on pore volume. This is necessary to improve the utility of positron annihilation lifetime spectroscopy as a porosimetric technique. The need to take the migration of positronium to larger free volume into account is discussed.
Źródło:: Acta Physica Polonica A; 2017, 132, 5; 1559-1563
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: Porosity of Silica Monoliths with Tailored Mesopores of Ink-Bottle Shape Determined by Nitrogen Adsorption and Positron Annihilation Lifetime Spectroscopy
Autorzy:: Sienkiewicz, A.
Kierys, A.
Gorgol, M.
Zaleski, R.
Powiązania:: https://bibliotekanauki.pl/articles/1033934.pdf
Data publikacji:: 2017-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 81.05.Rm
68.43.-h
81.70.-q
78.70.Bj
36.10.Dr
Opis:: The comparison of pore size distributions obtained with the use of two porosimetric methods: low temperature nitrogen sorption (LN2) and positron annihilation lifetime spectroscopy (PALS), was performed for porous silica monoliths. Four investigated samples were prepared under various synthesis conditions. Nitrogen sorption showed the presence of bottle-shaped pores in all investigated samples. In addition, it seems that the presence of methanol during synthesis influences porosity to a greater extent than organic additives. Quite good agreement between the LN2 and PALS results was observed only for the silica monolith synthesized with β-cyclodextrins as pore directing agent. The biggest discrepancy in the results obtained from these two techniques was observed for the silica gel synthesized with no additives. The origin of such discrepancies, taking into account the shape of pore size distribution and deficiencies of data analysis techniques, is discussed.
Źródło:: Acta Physica Polonica A; 2017, 132, 5; 1568-1571
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Measurement and Analysis of the Positron Annihilation Lifetime Spectra for Mesoporous Silica
Autorzy:: Zaleski, R.
Powiązania:: https://bibliotekanauki.pl/articles/2047164.pdf
Data publikacji:: 2006-11
Wydawca:: Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:: 78.70.Bj
36.10.Dr
61.43.Gt
81.07.-b
41.75.Fr
Opis:: Positron annihilation lifetime spectroscopy as a technique of porous materials investigation is still under development. Both measurement conditions and lifetime spectra analysis methods have to be adapted to the requirements of positron porosimetry. If complex positron annihilation lifetime spectra of porous materials are processed, numerical methods of lifetime spectra analysis have to be used with a particular care. Among various methods of positron annihilation lifetime spectra analysis available, the most popular ones were tested implemented in programs MELT and LT. It was found, from the simulated spectra study, that a large number of counts in a spectrum is needed to obtain reliable results of analysis. Even then only an approximate solution is available. Determination of the approximation nature helps in a further interpretation of the results and in positron annihilation lifetime spectrometer setting adequate to the problem. For this purpose, a few complex spectra obtained from positron beam facility were tested. The results show a negligible influence of resolution function on long lifetime components, while the precise estimation of the background level is crucial. Also some distortions caused by imperfection of numerical analysis methods are pointed out.
Źródło:: Acta Physica Polonica A; 2006, 110, 5; 729-738
0587-4246
1898-794X
Pojawia się w:: Acta Physica Polonica A
Dostawca treści:: Biblioteka Nauki

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