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A Comparison of Different Theoretical Models of Positron Lifetime Spectra for Polymers

100%
Kansy J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1397-1407
EN
The same reference positron lifetime spectra of polyurethane, measured in temperature range 112 to 390 K, were analyzed with three theoretical models: the "conventional" model with three exponential decay component of discrete values of lifetimes, a model with one discrete exponential component and two "packages" of exponentials with log-normal distribution of annihilation rates, and a model considering positronium slow localization, positronium internal relaxation as well as "delayed" formation of positronium. It turns out that the two latter models fit to the experimental data with the same excellent quality, in spite of the fact that in both models the ratio of intensities related to para-positronium and ortho-positronium was constrained to be as 1:3.
2
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Relationship between Enhanced Positronium Formation and Enhanced Positron Trapping in Polymers at Low Temperature

64%
Kansy J., Suzuki T.
Acta Physica Polonica A
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2006
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vol. 110
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issue 5
593-604
EN
Positron annihilation lifetime spectroscopy is used for investigation of low-density polyethylene and ethylene-methyl methacrylate copolymers of 1.45, 3.0, and 5.4 mole% of methyl methacrylate. The lifetime spectra are collected at 30 K, one by one, as a function of elapsed time. In the computer analysis a new theoretical model is developed, which enables separating the annihilation from positron free state, its trapped state and bound state in positronium. The positron trapping rateμ and the enhanced positronium formation rateκ are determined. The calculated values of μ andκ turned out to be linearly correlated. This correlation presumably originates from an influence of trapped electrons on the trapping of positrons. The dependences ofκ on measurement time are determined for low-density polyethylene and ethylene-methyl methacrylate of different methyl methacrylate content. A theoretical model describing quantitatively the dependences is proposed. The model considers the processes of electron-ion recombination, electron trapping, and electron scavenging by dipolar carbonyl groups supplied by methyl methacrylate additives.
3
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Correlations between Positron Annihilation Parameters and Macroscopic Properties in Copolymers Belonging to Elastomers Group

64%
Krzemień K., Kansy J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1435-1440
EN
The positron annihilation lifetime spectroscopy was used to study correlations between positron annihilation parameters and macroscopic properties in two kinds of polymers from elastomers group. Two kinds of material were investigated: three samples of ethylene octane copolymers (commercial name engage) of different densities and six samples of polybutylene terephtalate-polyether glycol copolymers (hytrel) having different densities. A correlation between intensity of ortho-positronium component and the density (d) of samples was observed for both kinds of material. From the ortho-positronium pick-off lifetime the mean radii (R) of free volume centers were determined. A good linear correlation between R and d was found.
4
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Hyperfine Interaction Parameters in Fe_{28}Al_{72}: ^{57}Fe Mössbauer Spectroscopy and Ab Initio Study

51%
Hanc A., Deniszczyk J., Kansy J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1154-1155
EN
The paper discusses a theoretical model that associates the shape of the Mössbauer spectrum with the configuration of atoms in local surroundings of the Mössbauer nuclide. Using the model we analyse the Mössbauer spectra of Fe_{72}Al_{28} alloys after various heat treatments. Basing on the model calculations the hyperfine structure parameters describing an effect of an Al atom in the first and the second coordination shell of ^{57}Fe atom are evaluated. Using these parameters the values of hyperfine magnetic field and isomers shift for the atomic configurations present in stoichiometric Fe_3Al are estimated and compared with the results of ab initio calculations.
5
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Positron Annihilation Lifetime in situ Study of Deformed Polyolefin Elastomers

51%
Krzemień K., Kansy J., Frąckowiak J.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
837-841
EN
The positron annihilation lifetime spectroscopy was used to investigate the free volume hole size of ethylene octane copolymers as a function of deformation in the range from 0 to 110% in steps of 10%. For each degree of deformation a series of 5-6 positron annihilation lifetime spectra was collected in situ. All spectra of a given series were analysed simultaneously. They were resolved into three exponential components, of lifetimes parametersτ_i and intensities I_i. The variations ofτ_3 reflect three deformation regions, the elastic range, strain softening range, and plastic region.
6
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Surface Concentration of Defects at Grain Boundaries in Sintered Alumina Determined by Positron Annihilation Lifetime Spectroscopy

51%
Kansy J., Si Ahmed A., Liebault J., Moya G.
Acta Physica Polonica A
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2001
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vol. 100
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issue 5
737-742
EN
Sintered alumina samples of grain diameters spanning from 1.2 to 4.5μm have been investigated by positron annihilation lifetime spectroscopy. One series of samples was produced from material containing about 150 ppm impurities (mainly SiO_2). The second one was made from material having about 2700 ppm of various elements (SiO_2, MgO, CaO). Two models of positron trapping at grain boundaries are compared: The first one relates to the diffusion-limited regime; and the other one - to the transition-limited regime of trapping. As a result the relative change of surface concentration of defects at grain boundaries is determined. Additionally, the positron diffusion constant in bulk alumina at room temperature, D_+=0.36±10 cm^2/s, is estimated.
7
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Influence of Heat Treatment on Ordering Process in Fe_{72}Al_{28} Alloy Studied by Mössbauer Spectroscopy

51%
Kansy J., Hanc A., Giebel D.
Acta Physica Polonica A
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2011
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vol. 119
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issue 1
44-47
EN
The paper discusses a theoretical model that associates the shape of Mössbauer spectrum with the configuration of atoms in local surroundings of the Mössbauer nuclide. The model has been implemented to a computer program which was used to analyse the Mössbauer spectra of Fe_{72}Al_{28} alloys after various heat treatments. Basing on the determined configuration of atoms, the long range ordering parameter was estimated.
8
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Vacancy Formation in Fe-Al of B2 and DO_3 Alloys

51%
Kansy J., Hanc A., Giebel D., Jabłońska M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1409-1415
EN
The positron lifetime spectroscopy is employed to study vacancy formation in intermetallic phases of DO_3 and B2 structures from Fe-Al system as a function of Al concentration, ternary additive (Cr) and their thermal treatment. Lifetime spectra were fitted en block by a simple trapping model encoded directly to the software (computer program LT-9). In the investigated range of Al concentration (28, 38, 42, and 45 at%) only two types of defects are found. In DO_3 region a single type of defects (characterized by positron lifetime τ_1=170±2 ps) is detected and indicated as vacancies in the Fe sublattice (V_{Fe}). In B2 region a small amount of an additional type of defects (characterized by positron lifetime τ_2=214±13 ps) appears. Supposedly, these are vacancies in Al sublattice (V_{Al}). For Fe28Al and Fe28Al5Cr samples changes in V_{Fe} concentration are determined as a function of the sample composition, annealing time at 1000°C and quenching the samples to air and oil. The defect concentration increases with increase in Al content. For FeAl with Al above 38 at%, the total concentration of defects is so high that positrons are exclusively trapped by defects. Therefore the concentrations V_{Al} and V_{Fe} cannot be determined separately. However, the ratio of V_{Al} concentration to V_{Fe} concentration is estimated as a function of Al content.
9
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Genetic Algorithms for Positron Lifetime Data

45%
Karbowski A., Fisz J., Karwasz G., Kansy J., Brusa R.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1365-1372
EN
Recently, genetic algorithms have been applied for ultrafast optical spectrometry in systems with several convoluted lifetimes. We apply these algorithms and compare the results with POSFIT (by Kirkegaard and Eldrup) and LT programme (by Kansy). The analysis was applied to three types of samples: molybdenum monocrystals, Czochralski-grown silicon with oxygen precipitates, Si with under-surface cavities obtained by He + H ion co- implantation. In all three tests, the genetic algorithm performs very well, in particular for short lifetimes. Further developments to model the resolution function in genetic algorithms are needed.
10
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Properties of Neutron Doped Multicrystalline Silicon for Solar Cells

39%
Pochrybniak C., Pytel K., Milczarek J., Jaroszewicz J., Lipiński M., Piotrowski T., Kansy J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 4
1255-1265
EN
The technology of neutron transmutation doping of silicon wafers in MARIA nuclear research reactor is described. The studies of the radiation defects performed with positron annihilation confirmed that divacancies dominate in the irradiated material. Thermal treatment of irradiated silicon at 700-1000°C produces void-phosphorus complexes and void aggregates. The resistivity of the samples produced by neutron transmutation doping was found to be uniform within 2.5% limits. The severe reduction of the minority carrier lifetime in irradiated samples was confirmed.
11
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A Study of Point Defects in the B2-Phase Region of the Fe-Al System by Mössbauer Spectroscopy

39%
Hanc A., Kansy J., Dercz G., Pająk L., Oleszak D., Mrzigod J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6
1555-1562
EN
In this work, we employed the Mössbauer spectroscopy and X-ray powder diffraction in a study of point defect formation in intermetallic phases of the B2 structure of the Fe-Al system as a function of Al concentration. The results are compared with the concentrations of point defect determined from positron annihilation data. In the Mössbauer effect, two types of samples are investigated: Fe-Al alloys with few additives obtained by induction melting and Al-rich metallic powders produced by the self-decomposition method and intensive grinding of high energy in the electro-magneto-mechanical mill. We present the values of the ^{57}Fe isomer shift and quadrupole splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentration of the Fe vacancies and Fe atoms substituting Al (Fe-AS) are determined. The results showed that an increase in Al content causes an increase in vacancy and Fe-AS concentration.
12
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Structural Relaxation in Fe_{78}Nb_{2}B_{20} Amorphous Alloy Studied by Mössbauer Spectroscopy

39%
Kansy J., Hanc A., Rasek J., Haneczok G., Pająk L., Stokłosa Z., Kwapuliński P.
Acta Physica Polonica A
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2011
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vol. 119
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issue 1
41-43
EN
It was shown that soft magnetic properties of Fe_{78}Nb_{2}B_{20} amorphous alloy can be significantly improved by applying 1-h annealing at temperature 623 K (permeability increases even about 8 times). The Mössbauer Spectroscopy technique indicated that the optimized microstructure (corresponding to the maximum magnetic permeability) is free of iron nanograins and should be attributed to annealing out of free volume and a reduction of internal stresses i.e. to the relaxed amorphous phase.
13
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Optimization of Soft Magnetic Properties in Fe₈₂Nb₂B₁₄RE₂ (RE = Y, Gd, Tb and Dy) Group of Amorphous Alloys

39%
Chrobak A., Haneczok G., Zivotsky O., Hendrych A., Kansy J., Kotur B.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
916-919
EN
Enhancement of soft magnetic properties in the selected group of amorphous alloys was examined by different experimental methods. It was shown that permeability for annealed samples (at T_{a} for 1 h; 300 K < T_{a} < 900 K) plotted vs. T_{a} shows a maximum at which is 700, 725, 725, and 750 K for Fe₈₂Nb₂B₁₄Y₂, Fe₈₂Nb₂B₁₄Gd₂, Fe₈₂Nb₂B₁₄Tb₂ and Fe₈₂Nb₂B₁₄Dy₂ alloy, respectively. For samples after the optimization annealing permeability is at least 10 times higher than in the as-quenched state. The optimized microstructure is free of iron nanograins and corresponds to so-called relaxed amorphous phase.
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