Full-text resources of PSJD and other databases are now available in the new Library of Science.
Visit https://bibliotekanauki.pl
Preferences help
Polish version English version Language
enabled [disable] Abstract
Number of results

Results found: 12

Number of results on page
first rewind previous Page / 1 next fast forward last

Search results

help Sort By:

help Limit search:
first rewind previous Page / 1 next fast forward last
1
Content available remote

Some Comments on p-Ps and Density Parameter

100%
Goworek T., Wawryszczuk J.
Acta Physica Polonica A
|
1995
|
vol. 88
|
issue 1
135-138
EN
The constraint-free analysis of several representative positron lifetime spectra was performed with the resolution time of 144 ps. The role of p-Ps parameters in understanding of the positronium structure in solids is discussed.
2
Content available remote

Positron Porosimetry Studies of Template Removal from As-Synthesized MCM-41 Silica

100%
Zaleski R., Wawryszczuk J.
Acta Physica Polonica A
|
2008
|
vol. 113
|
issue 5
1543-1550
EN
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).
3
Content available remote

Influence of Temperature and Pressure on the Free Volume in Thermo-Shrunken Polyethylene by Positron Annihilation

81%
Danch A., Osoba W., Wawryszczuk J.
Acta Physica Polonica A
|
2008
|
vol. 113
|
issue 5
1307-1313
EN
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.
4
Publication available in full text mode
Content available

Three-Quantum Annihilation in Porous Vycor Glass

81%
Jasińska B., Wawryszczuk J., Zaleski R.
Acta Physica Polonica A
|
2005
|
vol. 107
|
issue 5
821-825
EN
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.
5
Content available remote

Distortion of the Positron Lifetime Spectra in BaF_{2} Spectrometers

81%
Goworek T., Górniak W., Wawryszczuk J.
Acta Physica Polonica A
|
1993
|
vol. 83
|
issue 3
307-311
EN
High efficiency of BaF_{2} scintillators creates the risk of distortion of the positron lifetime distributions due to summing and backscattering. In the 180° geometry it leads to the appearance of a spurious shortlived component.
6
Publication available in full text mode
Content available

Vapour Absorption in Melamine-Formaldehyde Resin

81%
Wawryszczuk J., Ciesielski K., Goworek J.
Acta Physica Polonica A
|
2001
|
vol. 99
|
issue 3-4
523-528
EN
The effects of vapour absorption on positron annihilation in cross-linked polymer were investigated. Contrary to linear polymers, absorption of vapour in cross-linked resin leads to the shortening of o-Ps lifetime. In vacuum absorbed molecules diffuse out. At room temperature desorption of hexane and hexanol is not complete; full elimination of absorbed molecules requires sample temperature increase.
7
Publication available in full text mode
Content available

Positronium Formation in Solid Long-Chain Alkanes

81%
Zaleski R., Wawryszczuk J., Goworek T.
Acta Physica Polonica A
|
2005
|
vol. 107
|
issue 4
635-641
EN
This paper represents a fragment of systematic studies on positron annihilation in solid saturated hydrocarbons (alkanes, paraffins) from C_{17}H_{36} to C_{30}H_{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.
8
Publication available in full text mode
Content available

Ortho-Positronium in Some n-Alkanes; Influence of Temperature and Pressure

81%
Zgardzińska B., Pietrow M., Goworek T., Wawryszczuk J.
Acta Physica Polonica A
|
2006
|
vol. 110
|
issue 5
747-753
EN
Positron lifetime spectra were measured for a series of odd-numbered n-alkanes from C_{11}H_{24} to C_{19}H_{40} as a function of temperature and pressure. The ortho-Ps lifetimes in the rotator phase and the increase in intensity at the transition to that phase can be explained by location of Ps in the vicinity of kink-type conformers. The relation between o-Ps lifetime and molecule length can be described in the framework of extended Tao-Eldrup model. One can eliminate the effect of intensity rise in time by sample illumination or by application of high pressure. A decrease in temperature by 1 K is equivalent to an increase in pressure by about 4 MPa.
9
Publication available in full text mode
Content available

Pressure Effects in ortho-Positronium Annihilation

81%
Goworek T., Wawryszczuk J., Zaleski R.
Acta Physica Polonica A
|
2005
|
vol. 107
|
issue 4
608-614
EN
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.
10
Content available remote

An Attempt to Produce the Implanted ^{22}Na Source for Positron Spectrometry

61%
Latuszyński A., Yushkevich Y., Bystrov V., Misak R., Wawryszczuk J., Goworek T.
Acta Physica Polonica A
|
1993
|
vol. 83
|
issue 3
345-348
EN
Preliminary results of ^{22}Na implantation into the metal foils in order to produce the positron source for annihilation experiments are presented.
11
Publication available in full text mode
Content available

Testing the Extended Tao-Eldrup Model. Silica Gels Produced with Polymer Template

61%
Śniegocka M., Jasińska B., Wawryszczuk J., Zaleski R., Deryło-Marczewska A., Skrzypek I.
Acta Physica Polonica A
|
2005
|
vol. 107
|
issue 5
868-873
EN
The temperature dependence of o-Ps lifetime in the pores calculated from extended Tao-Eldrup model was compared to the experimental data, collected for a set of silica gels synthesized using the polymer template technique. For the sample with average pore radii 2.0 nm rather good agreement between the model and experiment was found. For the sample with narrow pores (near 1.0 nm) the lifetime spectrum was complex. Except the range of highest temperatures the lifetimes are far from model calculations.
12
Publication available in full text mode
Content available

The Temperature and Pressure Dependence of the Free Volume in Fluoroelastomers from PALS and PVT Experiments

52%
Dlubek G., Sen Gupta A., Wawryszczuk J., Kilburn D., Pionteck J., Krause-Rehberg R., Goworek T., Alam M., Kaspar H., Lochhaas K.
Acta Physica Polonica A
|
2005
|
vol. 107
|
issue 4
685-689
EN
Positron lifetime and pressure-volume-temperature experiments were performed as function of T (100-485 K) and P (10^{-5} Pa-500 MPa) on a fluoroelastomer. From positron annihilation lifetime spectroscopy, analyzed with LT9.0 assuming a dispersion in the e^+ (τ_2) and o-Ps (τ_3) lifetime, the mean, 〈v_h〉, and the width (standard deviation), σ_h, of the hole size distribution were calculated. The pressure-volume-temperature data were analyzed using the Simha-Somcynsky hole-lattice theory to estimate the specific hole free volume V_f. From a comparison of V_f with 〈v_h〉 the specific hole number, N'_h, is estimated. The data from thermal expansion and pressure experiments show complete agreement when taking into account the compressibility of the occupied volume.
first rewind previous Page / 1 next fast forward last
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.