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Wyświetlanie 1-15 z 307
Tytuł:
Formation and Annealing of Micropores in Hematite
Autorzy:
Dauwe, C.
Da Costa, G. M.
Van Hoecke, T.
Segers, D.
Powiązania:
https://bibliotekanauki.pl/articles/1933484.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
In iron oxide powders positrons are trapped in the surface layers and the value of the S-parameter is an indicator of the total specific surface, including external surface and internal surfaces of micropores. The evolution of micropores is followed when α-FeOOH is thermally decomposed into α-Fe$\text{}_{2}$O$\text{}_{3}$. It is shown that the micropore formation is not linked to the decomposition process, but that they also form in hematite synthesized from a ferrihydrite precursor in aqueous solution.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 119-123
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Remarks on Reconstruction of Defects Distribution by Positron Lifetime Measurements
Autorzy:
Dryzek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1933485.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
It is well known that the positron trapping rate obtained from positron lifetime measurements depends upon defect concentrations and trapping efficiency. If a distribution of open volume defects exists, a distribution of trapping efficiency also could be present. As an example, the calculation of trapping efficiency as a function of radius of defects in Al is presented. The correct explanation of defect size distribution obtained by positron lifetime measurements needs to introduce some additional assumptions about trapping efficiency.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 125-128
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Studies of the Cu-Mn System
Autorzy:
Nicht, E.-M.
Brauer, G.
Kajcsos, Zs.
Molnar, B.
Powiązania:
https://bibliotekanauki.pl/articles/1933529.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The superstructures Cu$\text{}_{3}$Mn and Cu$\text{}_{5}$Mn have been characterized for the first time by X-ray and differential scanning calorimetry measurements. In addition, positron lifetime measurements are presented in order to show the defect structure of these alloys. It turned out that the annealing behaviour is equal for the two different alloys and the two different deforming processes. An annealing temperature of 300°C is not sufficient to obtain a defect free state.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 205-210
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Annihilation Studies of the Ni-H Systems Containing Thermally Induced Crystal Lattice Defects
Autorzy:
Pająk, J.
Powiązania:
https://bibliotekanauki.pl/articles/1933538.pdf
Data publikacji:
1995-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The interaction between hydrogen and thermally induced defects has been studied in nickel samples using the positron annihilation technique. From measurements further evidence has been found for agglomeration of vacancies and small vacancy complexes into large-size three-dimensional void-like defects in the plastically deformed and electron beam irradiated samples containing hydrogen.
Źródło:
Acta Physica Polonica A; 1995, 88, 1; 219-223
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Kinetics of the Spin-Conversion of Positronium Measured by β$\text{}^{+}$γ∆E Age-Momentum Correlation
Autorzy:
Lauff, U.
Maier, K.
Major, J.
Seeger, A.
Stoll, H.
Wesołowski, P.
Koch, M.
Bilard, I.
Abbé, J.
Duplâtre, G.
Powiązania:
https://bibliotekanauki.pl/articles/1929104.pdf
Data publikacji:
1993-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
Age-momentum correlation (AMOC) measurements provide time-resolved information on the momentum distribution of annihilating electron-positron pairs through correlated determination of Doppler broadening (∆E) of the 511 keV annihilation radiation line and positron age. In the β$\text{}^{+}$γ∆E AMOC technique implemented at the Stuttgart pelletron accelerator the start signals for the age measurements are generated when the relativistic positrons pass through a fast plastic scintillator, which has a detection efficiency close to unity. Beam-based β$\text{}^{+}$γ∆E AMOC measurements thus combine high β$\text{}^{+}$γ∆E triple-coincidence rates with low background. From a practical point of view this constitutes a major progress compared to conventional (source-based) γγ∆E AMOC measurements. The AMOC technique permits direct access to a wide variety of time-dependent processes, among them the reaction kinetics in positronium chemistry. As an example, we present a β$\text{}^{+}$γ∆E AMOC investigation of the kinetics of a spin-conversion reaction of positronium in methanol induced by the presence of a nitrosyl free-radical paramagnetic solute (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl , HTEMPO). The AMOC measurements allowed the time-resolved observation of the spin-conversion process, which had been investigated before by uncorrelated positron lifetime and Doppler-broadening measurements. It is found that within the concentration range investigated (≤ 0.1 mol/l) the spin-conversion reaction rate at room temperature depends linearly on the HTEMPO concentration with a reaction-rate constant k$\text{}_{conv}$ = (22.5 ± 0.5) × 10$\text{}^{9}$ l mol$\text{}^{-1}$ s$\text{}^{-1}$.
Źródło:
Acta Physica Polonica A; 1993, 83, 3; 349-358
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Use of Energy Summing for Selection of Coincidence Events in Positron-Lifetime Spectroscopy
Autorzy:
Bec̆vár̆, F.
C̆iz̆ek, J.
Procházka, I.
Powiązania:
https://bibliotekanauki.pl/articles/2007883.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
A BaF$\text{}_{2}$ positron-lifetime spectrometer equipped with a coincidence system that represents a compromise between the traditional fast-fast and fast-slow arrangements is described. The main difference of the present configuration from both the fast-slow and fast-fast ones consists in use of a sum of the energy signals from the start and stop detectors to select the coincidence events. Quality of the spectrometer response function (≈ 150 ps FWHM for $\text{}^{22}$Na) is very close to that observed for our fast-slow configuration with the equivalent detectors but throughput of the present apparatus is increased almost by a factor of two. Moreover, the electronic scheme becomes less complicated, which has also a positive impact on its cost.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 448-454
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positronium in Small and Large Voids in Vycor Glass
Autorzy:
Ciesielski, K.
Dawidowicz, A. L.
Goworek, T.
Powiązania:
https://bibliotekanauki.pl/articles/2007951.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The intensities of ortho-positronium components related to the pores and to small voids in the bulk were determined for a series of Vycor glasses. The ratio of "pore fraction" to the total o-Ps yield depends on the specific surface area of the porous medium. The diffusion coefficient for o-Ps was found equal to 3.7×10$\text{}^{-5}$ cm$\text{}^{2}$/s.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 483-486
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Trapping Model in Fine Grained Sample
Autorzy:
Dryzek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2007999.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
In the paper we consider the positron trapping model in the sample where the spherical particles were immersed in the medium. The radius of the particles was small enough to take into account the diffusion of positrons. We present the exact solutions of the model for two cases, when transition of the positrons from the particle to the medium was neglected and when it was taken into consideration. The theoretical calculations were applied to description of the positron annihilation in the copper sample where the recrystallization process took place.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 539-545
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Positron Annihilation in Deformed and Hydrogenated Pd-23%atcu Alloy
Autorzy:
Pająk, J.
Szatanik, R.
Szuszkiewicz, M.
Powiązania:
https://bibliotekanauki.pl/articles/2008180.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
Peak coincidence counting rate and positron lifetime spectra for deformed by cold-rolling, and annealed by four hours in the temperature 973 K, hydrogen free and hydrogenated PdCu with 23% Cu samples, in the temperature range from room temperature to about 720 K were measured. It was found that hydrogen improved to tempered samples creates defects that are annealed to the temperature about 525 K. In the cold-rolled up to deformation degree of 50% samples, hydrogen is trapped at defects, probably vacancies, forming H-V complexes, that become disappearing in the vicinity of the temperature at 350 K.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 637-640
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Measurements of Positrons Lifetimes in Corroded Nickel
Autorzy:
Pietrzak, R.
Szatanik, R.
Szuszkiewicz, M.
Powiązania:
https://bibliotekanauki.pl/articles/2008182.pdf
Data publikacji:
1999-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
An attempt was undertaken at making use of a technique of taking measurements of lifetimes of positrons emitted from $\text{}^{22}$Na source to investigate corroded nickel. It was found that after corrosion in HCl vapours mean positrons lifetime, the second component of positrons lifetimes as well as its intensity rise along with the corrosion time.
Źródło:
Acta Physica Polonica A; 1999, 95, 4; 647-651
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A Study of Positron Properties in Quartz Crystals and Synthetic Silica Glass
Autorzy:
Anwand, W.
Brauer, G.
Hasegawa, M.
Dersch, O.
Rauch, F.
Powiązania:
https://bibliotekanauki.pl/articles/2024077.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The monoenergetic positron beamline "SPONSOR" at Rossendorf has been used to investigate the positron behaviour in a naturally grown Brasilian quartz, two synthetic quartz crystals of different origin, and synthetic silica glass. The measurements allow us to obtain the positron diffusion length of free positrons and Bloch para-positronium, if formed, in these materials. In addition, hydrothermal treatment of a synthetic quartz has been used to introduce hydrogen into the crystal up to a certain depth. The presence of hydrogen is found to influence the formation of para-positronium. The depth distribution of hydrogen has been measured independently by nuclear reaction analysis, and will be discussed in comparison with the results deduced from the positron studies.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 321-328
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Algorithm for Shifting Positron Annihilation Spectra
Autorzy:
Dryzek, J.
Polak, A.
Powiązania:
https://bibliotekanauki.pl/articles/2024230.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
We present a simple procedure which allows us to shift the positron annihilation spectra, e.g., the Doppler broadening spectrum of the annihilation line. That is especially required when we wish to compare different spectra obtained with a spectrometer with the reduction of background. As an application of the obtained algorithm we present the studies of positron annihilation in carbon material samples.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 355-361
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Study of Defects in GeTe and (GeTe)$\text{}_{1-x}$(AgBiTe_2)_x Solid Solutions by Positrons
Autorzy:
Misheva, M.
Avramova, I.
Plachkova, St.
Djourelov, N.
Powiązania:
https://bibliotekanauki.pl/articles/2025145.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
Positron lifetimes and Doppler broadening of the annihilation line measurements were performed to study the vacancy type defects in polycrystalline GeTe and (GeTe)$\text{}_{(1-x)}$(AgBiTe$\text{}_{2}$)$\text{}_{x}$ (x=0,0.03,0.05,0.1,0.15,0.2, and 1) solid solutions. The values of lifetimes obtained are explained as due to positron and positronium saturated trapping at vacancies and vacancy clusters. The interdependence between mean positron lifetime and hole concentration is discussed.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 423-428
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect of Annealing on Free-Volume Properties of Poly(ethylene Terephthalate) Studied by Positron Annihilation
Autorzy:
Misheva, M.
Djourelov, N.
Seganov, I.
Powiązania:
https://bibliotekanauki.pl/articles/2025732.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
The effect of annealing on free-volume properties of poly( ethylene terephthalate) was studied using a set of samples annealed for two hours in air at eight temperatures between 80ºC and 220ºC. The fractional free-volume in the samples was estimated from ortho-positronium lifetime and its relative intensity. The variations of fractional free-volume and of the macroscopic specific volume with annealing temperature were compared. The variation of the pore volume probability density functions with the annealing temperature was found. The interdependence between S- and W-parameters was also discussed.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 429-433
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Some Aspects of Positronium Interaction with Elementary Free Volumes in Polymers
Autorzy:
Shantarovich, V. P.
Powiązania:
https://bibliotekanauki.pl/articles/2025763.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
This paper contains a discussion of original and recently published results on positronium annihilation lifetime studies of elementary free volumes in the group of polymer glasses. The results are used for indication of non-homogeneity of these materials and give some basis for considering a connection of the long-lived component intensities I$\text{}_{3}$(I$\text{}_{4}$) with concentrations N$\text{}_{3}$(N$\text{}_{4}$) of elementary free volumes and, in this way, with fractional free volume.
Źródło:
Acta Physica Polonica A; 2001, 99, 3-4; 487-495
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 307

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