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    Wyświetlanie 1-9 z 9
    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:
    Anisotropic Magnetic Quenching of Positronium Formed by Polarized Positrons in Oriented Crystals
    Autorzy:
    Bondarev, I. V.
    Powiązania:
    https://bibliotekanauki.pl/articles/2007885.pdf
    Data publikacji:
    1999-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.60.+z
    36.10.Dr
    Opis:
    A theoretical analysis is performed of the phenomenon of anisotropic magnetic quenching of a positronium atom formed by polarized positrons in noncubic crystals oriented with respect to an external magnetic field. An initial polarization of positrons is shown to enhance an anisotropy of Ps magnetic quenching and to decrease the strength of magnetic field in which an anisotropy is maximal. A maximal anisotropic effect has been estimated for quasi-Ps in crystalline quartz and Ps complex in naphthalene single crystal.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 4; 455-460
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Polypropylene Films Studied with Variable Positron Beams
    Autorzy:
    Dębowska, M.
    Coleman, P. G.
    Gidley, D. W.
    Powiązania:
    https://bibliotekanauki.pl/articles/2007958.pdf
    Data publikacji:
    1999-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    36.10.Dr
    61.41.+e
    71.60.+z
    78.70.Bj
    Opis:
    Doppler broadening and positron lifetime spectra have been measured for polypropylene films of constant thickness (≈ 50 μm) and different morphology that crystallized from melt at temperature 0, 100, and 120°C. The S -parameter vs. energy curves do not change in a systematic way with crystallinity of samples. It is supposed that decrease in the fractional free volume for samples of greater crystallinity is not seen in S-values because of their increase resulting from annihilation in defects present both in the crystalline regions and on the lamellae surfaces. Intensities of the components in the positron lifetime spectra: I$\text{}_{2}$ (τ$\text{}_{2}$=1.3 ns) and I$\text{}_{3}$ (τ$\text{}_{3}$≈ 2.3÷2.8 ns) show changes with crystallinity of samples. The evident trend is observed for the longer-lived τ$\text{}_{3}$-component intensity to decrease with crystallinity while the reverse is true for the shorter, fixed τ$\text{}_{2}$-component. The decrease in the intensity of the longer-lived component can result from reduction of the fractional free volume.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 4; 496-504
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Analysis of Possible Scattering Processes for Bloch Positronium in Ionic Crystals at Elevated Temperatures
    Autorzy:
    Bondarev, I. V.
    Powiązania:
    https://bibliotekanauki.pl/articles/2024215.pdf
    Data publikacji:
    2001
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.60.+z
    71.38.+i
    36.10.Dr
    Opis:
    The role of nonpolar optic phonon scattering and of umklapp acoustic phonon scattering is analyzed for a delocalized positronium atom in ionic crystals at elevated temperatures. At temperatures above which they become essential both of these scattering mechanisms contribute to the imaginary self-energy of positronium renormalizing its acoustic deformation potential constant. It was such a renormalization that was recently observed experimentally for delocalized positronium in MgF$\text{}_{2}$ crystal. We put forward the theoretical explanation of these experiments based upon the model of nonpolar optic phonon scattering of positronium. An effect analogous to that observed in MgF$\text{}_{2}$ is predicted for crystalline quartz above the temperature of (α-β)-phase transition.
    Źródło:
    Acta Physica Polonica A; 2001, 99, 3-4; 337-343
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Sensitivity of Positronium Momentum Distribution to Phase Transitions in Crystalline Dielectrics
    Autorzy:
    Bondarev, I. V.
    Hyodo, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042201.pdf
    Data publikacji:
    2005-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.60.+z
    71.38.-k
    36.10.Dr
    Opis:
    We give a review of recent theoretical and experimental study of the positronium-phonon and positronium-quadrupole interactions in dielectric crystals of different local symmetries, placing a special emphasis on the sensitivity of the positronium momentum distribution to the second order phase transitions in crystalline dielectrics.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 4; 673-684
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ortho-Positronium in Alkanes under High Pressure
    Autorzy:
    Goworek, T.
    Zgardzińska, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812529.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    36.10.Dr
    61.80.Fe
    71.60.+z
    78.70.Bj
    Opis:
    Phase transitions in n-alkanes were observed by using the positron annihilation lifetime method. In the case of alkanes, application of pressure is equivalent to temperature lowering (1 K corresponds to ≈4 MPa). When argon at high pressure penetrates the sample one observes a non-monotonous dependence of the melting point on pressure. This effect is observed also in even-numbered alkanes, in which there is no rotator phase.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1379-1383
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positronium in Phase IV and Rotator Phase of Long-Chain Alkanes
    Autorzy:
    Zgardzińska, B.
    Goworek, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812555.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    36.10.Dr
    61.80.Fe
    71.60.+z
    78.70.Bj
    Opis:
    Ortho-positronium lifetime and intensity was measured as a function of temperature and pressure for some n-alkanes in which so-called "phase IV" appears. This phase is characterized by slightly increased ortho-positronium lifetime compared to low-temperature phases. It was found that the effect of quenching positronium by light does not appear in all phases from phase IV upwards. The lifetime in the rotator phases becomes equal to that in liquids, and only the change of positronium formation intensity allows to detect the solid-liquid transition in positron lifetime measurements.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1551-1555
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ortho-Positronium in Some n-Alkanes; Influence of Temperature and Pressure
    Autorzy:
    Zgardzińska, B.
    Pietrow, M.
    Goworek, T.
    Wawryszczuk, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047166.pdf
    Data publikacji:
    2006-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    36.10.Dr
    61.80.Fe
    71.60.+z
    78.70.Bj
    Opis:
    Positron lifetime spectra were measured for a series of odd-numbered n-alkanes from C$\text{}_{11}$H$\text{}_{24}$ to C$\text{}_{19}$H$\text{}_{40}$ 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.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 5; 747-753
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Quadrupole Interactions and Anisotropic Magnetic Quenching of Positronium in Oriented Crystals
    Autorzy:
    Bondarev, I. V.
    Kuten, S. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933475.pdf
    Data publikacji:
    1995-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Βj
    36.10.Dr
    31.30.Gs
    Opis:
    The quadrupole interaction of positronium in noncubic defectless crystals has been investigated theoretically. It is shown to lead to the weak anisotropy of positronium magnetic quenching. The temperature dependence of the quadrupole coupling constant and the estimations of the magnitude of the anisotropy are obtained for delocalized positronium in crystalline quartz. The significant magnitude of the anisotropy is predicted for "anomalous" positronium in oriented crystalline polymeric structures.
    Źródło:
    Acta Physica Polonica A; 1995, 88, 1; 83-90
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-9 z 9

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