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    Wyświetlanie 1-13 z 13
    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:
    Defect Recovery in α-Fe e$\text{}^{-}$-irradiated at 300 K
    Autorzy:
    Dai, G. H.
    Li, X. H.
    Moser, P.
    Moya, G.
    Van Duysen, J. C.
    Powiązania:
    https://bibliotekanauki.pl/articles/1928989.pdf
    Data publikacji:
    1993-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.70.Bv
    61.80.Fe
    78.70.Bj
    Opis:
    Defect annealing recovery has been studied, by measuring positron lifetime spectra, in high-purity α-iron irradiated at 300 K with 3 MeV electrons to a fluency of 7 × 10$\text{}^{19}$ cm$\text{}^{-2}$. Vacancy clusters containing 6-10 single vacancies were observed immediately after irradiation during which they were possibly forming (the so-called "irradiation annealing"). With increasing temperature, the agglomerates continually grow in size at the expense of their concentration, giving rise to the formation of microvoids (> 15 vacancies). Also present were other types of defects, probably immobile vacancies trapped by impurity (e.g. carbon) atoms and dislocation/loops generated presumably from collapse of voids during the relatively high dose irradiation and/or the annealing. The immobile vacancies eventually became movable at around 350 K, supplying the growing clusters and thus leading to a stabilization in their concentration till around 500 K. Between 500 and 700 K, microvoids gradually evaporated, but the dislocation-associated defects were able to survive annealing at temperatures as high as 700 K. The void size and concentration and their evolution have been evaluated on the basis of both the to date theoretical and experimental studies. The temperature dependence was also, observed of positron trapping into vacancy agglomerates of various sizes.Za
    Źródło:
    Acta Physica Polonica A; 1993, 83, 3; 277-286
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positron Annihilation Studies of Czochralski-Grown Silicon Annealed Under Pressure
    Autorzy:
    Karwasz, G. P.
    Brusa, R. S.
    Misiuk, A.
    Zecca, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2008074.pdf
    Data publikacji:
    1999-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    71.55.Cn
    Opis:
    Two positron techniques have been applied to study dynamics of oxygen precipitation in Czochralski-grown silicon, annealed under high (up to 1.4 GPa) pressure. Lifetime measurements were performed with 180 ps resolution; Doppler broadening with a variable-energy slow-positron beam. Different thermal treatings rise the mean lifetime of positrons from 222 ps in as-grown samples up to 227 ps. In samples with a high (up to 85%) amount of oxygen precipitated, an intermediate (550-800 ps) lifetime is observed.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 4; 575-580
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Porosity of Low-κ Materials Studied by Slow Positron Beam
    Autorzy:
    Brusa, R. S.
    Macchi, C.
    Mariazzi, S.
    Karwasz, G. P.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042213.pdf
    Data publikacji:
    2005-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    68.60.Dv
    68.90.+g
    Opis:
    The information about porosity in low-κ materials obtainable by depth profiling with positron annihilation spectroscopy is reviewed. In particular we focus on Doppler broadening spectroscopy and 2-3γ ratio of positronium measurements on SiOCH and amorphous carbon a-C:F:H thin films produced by plasma enhanced chemical vapour deposition.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 4; 702-711
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positrons and Positronium Atoms in a Condensed Phase Close to Its Melting Point
    Autorzy:
    Stepanov, S.
    Zvezhinskiy, D.
    Byakov, V.
    Duplâtre, G.
    Stepanov, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1196038.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    34.80.Lx
    78.70.Bj
    82.30.Gg
    Opis:
    Investigation of the local heating effect at the terminal part of a fast positron track sheds light on the accumulation of defects in a frozen medium close to its melting point. Estimations of the formation energies of the structural defects which may trap the Ps atom as well as a contribution of these defects to the enthalpy of fusion are obtained.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 691-695
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Amorphous Carbon Thin Films Deposited on Si and PET: Study of Interface States
    Autorzy:
    Mariazzi, S.
    Macchi, C.
    Karwasz, G. P.
    Brusa, R. S.
    Laidani, N.
    Bartali, R.
    Gottardi, G.
    Anderle, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2043339.pdf
    Data publikacji:
    2005-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    68.55.Ac
    71.60.+z
    73.20.At
    78.70.Bj
    Opis:
    Thin carbon films with various thicknesses, deposited on different substrates (Si and poly-ethylene-terephthalate) at the same operating conditions in a radio frequency plasma enhanced chemical vapour deposition system were characterized by Doppler broadening spectroscopy. The films and the substrates were depth profiled by a slow positron beam. The aim of these measurements was to study the open volume structure and the interface of the films. It was found that, independently from the substrate, the films were homogeneous and exhibited the same open volume distribution. On the contrary, the effective positron diffusion length in the Si substrate was found to change with the thickness of the carbon films. This behaviour was interpreted as a change in the electric field at the carbon/silicon interface.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 5; 842-847
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Systematic Measurements of Doppler-Coincidence Spectra for Positron Annihilation in Pure Metals and Semiconductors
    Autorzy:
    Deng, W.
    Pliszka, D.
    Brusa, R. S.
    Karwasz, G. P.
    Zecca, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2030758.pdf
    Data publikacji:
    2002-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    Opis:
    Doppler-broadening measurements of the electron-positron annihilation line in twenty six elements are presented. The adopted coincidence technique allows to reduce the background and point out the contribution of positron annihilation with core electrons. The changes of the high momentum contribution is presented for selected examples and a semiempirical analysis of the dependence on electronic structure is performed. Measured data are in a good agreement with recent theoretical calculations and can be used to identification of impurities surrounding open volume defects.
    Źródło:
    Acta Physica Polonica A; 2002, 101, 6; 875-892
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positrons and Positroniu m in Grainy and Porous Solids
    Autorzy:
    Kajcsos, Zs.
    Liszkay, L.
    Duplâtre, G.
    Varga, L.
    Lázár, K.
    Pál-Borbély, G.
    Beyer, H.
    Lohonyai, L.
    Caullet, P.
    Patarin, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2025110.pdf
    Data publikacji:
    2001
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    36.10.Dr
    61.43.Gt
    Opis:
    Systematic investigations have been performed using positron annihilation techniques on micrograins of crystalline powders (e.g., MgO, Al$\text{}_{2}$O$\text{}_{3}$, SiO$\text{}_{2}$) and on various zeolites (e.g., silicalite 1, Na-X, Na-Y, ZSM-5, mordenite) aiming at a better under standing of the formation and decay of the long-lived ortho-positronium states. The techniques were lifetime spectroscopy, Doppler-effect measurements and the recording of the full energy distribution of the annihilation radiation. The influences of heat treatment, sample evacuation and presence of gases were investigated. Lifetimes over 130 ns and o-Ps fractions of about 30% were found. A strong correlation of positron annihilation technique data with a water content of the samples was evidenced. Possible pictures of the formation and decay of ortho-positronium in porous media are discussed.
    Źródło:
    Acta Physica Polonica A; 2001, 99, 3-4; 399-406
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positronium Trapping in Porous Solids: Means and Limitations for Structural Studies
    Autorzy:
    Kajcsos, Zs.
    Liszkay, L.
    Duplâtre, G.
    Varga, L.
    Lohonyai, L.
    Pászti, F.
    Szilágyi, E.
    Lázár, K.
    Kótai, E.
    Pál-Borbély, G.
    Beyer, H. K.
    Caullet, P.
    Patarin, J.
    Azenha, M. E.
    Gordo, P. M.
    Lopes Gil, C.
    de Lima, A. P.
    Ferreira Marques, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042216.pdf
    Data publikacji:
    2005-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    36.10.Dr
    78.70.Bj
    61.43.Gt
    Opis:
    Positron annihilation techniques are used for the structural investigation of solids but the interpretation of results in grainy and porous media is still unclear. A unique picture can be obtained assuming that the dominant process is Ps trapping in competing "extended free volume" sites. In samples with a large amount of free volumes near-saturation Ps trapping will rule the lifetime pattern, and very long lifetimes of over 100 ns might arise from o-Ps trapped in mesopores. It is shown that lifetime parameters must be corrected for the 3γ/2γ counting efficiency ratio. The results demonstrate the high sensitivity of Ps to mesopores in zeolites but also that Ps-trapping poses limitations on the applicability of lifetime to structural investigation in porous systems. The evolution of the lifetime spectra upon changes in the sample and measuring conditions should be considered in a complex way, observing not only changes in some selected components but in the whole lifetime pattern simultaneously.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 5; 729-737
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Structural Studies of Titanium Oxide Multilayers
    Autorzy:
    Karwasz, G. P.
    Miotello, A.
    Zomer, E.
    Brusa, R. S.
    Kościelska, B.
    Armellini, C.
    Kuzmin, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2043379.pdf
    Data publikacji:
    2005-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    82.47.Jk
    78.70.Bj
    61.10.Nz
    Opis:
    Multilayers of titanium oxide on conductive glasses (silica, covered with indium/tin and tin oxides) were obtained by different methods (from suspension, by sol-gel, by vacuum sputtering). X-ray diffraction and positron annihilation depth-resolved characterization of these samples are presented. The data allow us to determine optimal deposition parameters, in order to obtain the anatase phase, important in practical applications in photoelectrochemical cells.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 6; 977-982
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Surfaces of Electron-Emitting Glasses Studied by a Slow Positron Beam
    Autorzy:
    Pliszka, D.
    Gazda, M.
    Kusz, B.
    Trzebiatowski, K.
    Karwasz, G. P.
    Deng, W.
    Brusa, R. S.
    Zecca, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2025748.pdf
    Data publikacji:
    2001
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    Opis:
    Semi-conducting glasses used for electron multipliers and microchannel plate devices are obtained by surface modification of Pb or Bi-reach silicon-based glasses. The reduced layer extends down to 200-500 nm, much more than the effective depth of the electron-emitting layer. By the use of slow-positron beam we monitor the structural changes undergoing in near-to-surface layers after isothermal annealing. The measurements suggest a possible correlation between secondary-electron emission coefficient and the Doppler-broadening S-parameter. On these samples there were also performed atomic force microscopy, secondary electron emission, differential scanning calorimetry, and electric conductivity measurements.
    Źródło:
    Acta Physica Polonica A; 2001, 99, 3-4; 465-472
    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:
    Positronium for antihydrogen production in the AEGIS experiment
    Autorzy:
    Consolati, G.
    Aghion, S.
    Amsler, C.
    Bonomi, G.
    Brusa, R.
    Caccia, M.
    Caravita, R.
    Castelli, F.
    Cerchiari, G.
    Comparat, D.
    Demetrio, A.
    Di Noto, L.
    Doser, M.
    Evans, C.
    Fanì, M.
    Ferragut, R.
    Fesel, J.
    Fontana, A.
    Gerber, S.
    Giammarchi, M.
    Gligorova, A.
    Guatieri, F.
    Haider, S.
    Hinterberger, A.
    Holmestad, H.
    Kellerbauer, A.
    Khalidova, O.
    Krasnicky, D.
    Lagomarsino, V.
    Lansonneur, P.
    Lebrun, P.
    Malbrunot, C.
    Mariazzi, S.
    Marton, J.
    Matveev, V.
    Mazzotta, Z.
    Müller, S.
    Nebbia, G.
    Nedelec, P.
    Oberthaler, M.
    Pacifico, N.
    Pagano, D.
    Penasa, L.
    Petracek, V.
    Prelz, F.
    Prevedelli, M.
    Ravelli, L.
    Rienaecker, B.
    Robert, J.
    Røhne, O.
    Rotondi, A.
    Sandaker, H.
    Santoro, R.
    Smestad, L.
    Sorrentino, F.
    Testera, G.
    Tietje, I.
    Widmann, E.
    Yzombard, P.
    Zimmer, C.
    Zmeskal, J.
    Zurlo, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1057954.pdf
    Data publikacji:
    2017-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    04.80.Cc
    07.77.-n
    36.10.Dr
    78.70.Bj
    Opis:
    The primary goal of the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEGIS) collaboration is to measure for the first time precisely the gravitational acceleration of antihydrogen, H̅, a fundamental issue of contemporary physics, using a beam of antiatoms. Indeed, although indirect arguments have been raised against a different acceleration of antimatter with respect to matter, nevertheless some attempts to formulate quantum theories of gravity, or to unify gravity with the other forces, consider the possibility of a non-identical gravitational interaction between matter and antimatter. We plan to generate H̅ through a charge-exchange reaction between excited Ps and antiprotons coming from the Antiproton Decelerator facility at CERN. It offers the advantage to produce sufficiently cold antihydrogen to make feasible a measurement of gravitational acceleration with reasonable uncertainty (of the order of a few percent). Since the cross-section of the above reaction increases with n⁴, n being the principal quantum number of Ps, it is essential to generate Ps in a highly excited (Rydberg) state. This will occur by means of two laser excitations of Ps emitted from a nanoporous silica target: a first UV laser (at 205 nm) will bring Ps from the ground to the n=3 state; a second laser pulse (tunable in the range 1650-1700 nm) will further excite Ps to the Rydberg state.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 5; 1443-1449
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-13 z 13

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