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    Wyświetlanie 1-12 z 12
    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:
    Influence of Positron Irradiation on Positronium Formation in n-Alkanes
    Autorzy:
    Pietrow, M.
    Zgardzińska, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047152.pdf
    Data publikacji:
    2006-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    36.10.Dr
    61.80.Fe
    78.70.Bj
    Opis:
    Positronium formation probability was investigated as a function of irradiation time and temperature for some long-chain saturated hydrocarbons (alkanes). Intensity of ortho-positronium component in the lifetime spectrum depends on the concentration of trapped excess electrons, but also on concentration of radicals and ions acting as electron scavengers. The results indicate the existence of two kinds of electron traps; those which are not emptied by thermal treatment disappear after several days of positron irradiation.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 5; 641-648
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Revision of the Model of Formation of Radiolytic Products in Aqueous Solutions
    Autorzy:
    Stepanov, S. V.
    Byakov, V. M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042192.pdf
    Data publikacji:
    2005-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.80.Fe
    36.10.Dr
    78.70.Bj
    Opis:
    Mathematical model of formation of radiolytic products (e$\text{}_{aq}^{-}$, H, OH, H$\text{}_{2}$, H$\text{}_{3}$O$\text{}^{+}$, OH$\text{}^{-}$, Ps) in water is developed. It takes into account (1) reactions between dissolved scavengers of thermalized and hydrated electrons as well as epithermal ones; (2) ambipolar diffusion expansion of the intratrack species; (3) additional channels of Ps and H$\text{}_{2}$ formation due to appearance of weakly trapped electrons. Good agreement is obtained with experimental data on kinetics of accumulation of the products in pure water and their concentration variations in aqueous solutions.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 4; 651-660
    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:
    Relationship between Enhanced Positronium Formation and Enhanced Positron Trapping in Polymers at Low Temperature
    Autorzy:
    Kansy, J.
    Suzuki, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047130.pdf
    Data publikacji:
    2006-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.60.+z
    61.80.Fe
    Opis:
    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.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 5; 593-604
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Experimental Verification of the Blob Model and Delayed Formation of Ps
    Autorzy:
    Dauwe, C.
    Van Waeyenberge, B.
    De Baerdemaeker, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042183.pdf
    Data publikacji:
    2005-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    36.10.Dr
    78.70.Bj
    61.80.Fe
    82.35.Lr
    Opis:
    Stepanov and Byakov's blob model for the formation of positronium can be considered as an extension of the spur model. However, it offers many extra possibilities and is more sound from the radiation chemistry point of view. A full coding of this model leads to non-exponential lifetime spectra, and standard multi-component analysis is no longer adequate for materials such as polymers. Age momentum correlation experiments were performed on linear PMMA at different temperatures and were analyzed with the non-exponential blob model. We show the adequacy of this model, and moreover an alternative explanation for the young-age broadening and delayed formation of positronium.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 4; 623-628
    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:
    Doppler Broadening and Positron Lifetime Measurements of Well-Characterized Sandstone and Limestone Rocks
    Autorzy:
    Urban, J. M.
    Quarles, C. A.
    Salaita, G. N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933548.pdf
    Data publikacji:
    1995-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    91.60.-x
    78.70.Bj
    61.80.Fe
    Opis:
    We measured the S parameter for samples of well-characterized rocks. Some samples were cleaned while others contained natural hydrocarbons. We also saturated some samples with oil. Preliminary results show a difference in the S parameter for sandstone and limestone samples. There is also a significant difference between samples when clean and when containing natural hydrocarbons or when saturated with light oil. We also measured the lifetime spectrum for the same samples in dry, fresh water-saturated, and brine-saturated condition. The observed lifetime spectra could be described with two or three components. While a detailed understanding of the physical processes responsible for the lifetime spectra is still under study, several interesting results have been obtained. The average lifetime is correlated with the S parameter. The porosity of the samples is correlated with the intensity of the third lifetime component. The average lifetime, as well as the second lifetime component, is systematically longer in the sandstone than limestone samples, and in water or brine-saturated samples. The intensity of the third lifetime component is generally larger in the water or brine-saturated samples.
    Źródło:
    Acta Physica Polonica A; 1995, 88, 1; 241-248
    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:
    Role of Trapped and Solvated Electrons in Ps Formation
    Autorzy:
    Stepanov, S. V.
    Byakov, V. M.
    He, C.
    Hirade, T.
    Mikhin, K. V.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042190.pdf
    Data publikacji:
    2005-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.80.Fe
    36.10.Dr
    78.70.Bj
    82.35.Lr
    Opis:
    Role of trapped and solvated electrons in Ps formation is discussed. Combination of thermalized positron with such electrons is possible from the viewpoint of the energy balance and may results in Ps formation. This process proceeds during all e$\text{}^{+}$ lifetime in matter. Fitting of raw experimental e$\text{}^{+}$ - e$\text{}^{-}$ annihilation spectra has to be based on an adequate physical input, which often leads to necessity of nonexponential deconvolution of the spectra. We have interpreted the Ps formation data in polyethylene, ethylene-methylmethacrylate and polymethylmethacrylate in dark and in light vs. time of the measurement and temperature. Parameters characterized accumulation of trapped electrons and their recombination with counter ions and positrons are obtained.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 4; 642-650
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Investigation of PCM Microcapsules with Paraffin Filling by Positron Lifetime Spectroscopy
    Autorzy:
    Zgardzińska, B.
    Powiązania:
    https://bibliotekanauki.pl/articles/1402636.pdf
    Data publikacji:
    2015-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    62.23.Pq
    61.80.Fe
    61.72.-y
    61.46.-w
    81.07.Nb
    64.70.Nd
    82.35.Pq
    Opis:
    Positron annihilation lifetime spectroscopy was applied to investigate the microcapsules composed of n-eicosane (filling material) and polysiloxane polymer (shell) in the range of temperatures 123-333 K. Pure components of microcapsules were also investigated as a base for interpretation of the measurement results. The temperature of phase transitions in microcapsules was determined. It showed the appearance of a rotary phase, which is not present in pure n-eicosane. In the considered material, two types of free volume have been identified. The sizes of free volumes able to accommodate Ps were estimated using standard models. On the basis of the o-Ps intensities, the content of polysiloxane in microcapsules was estimated as about 40%. Internal structure of the microcapsules (morphology) was observed by scanning electron microscopy.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 5; 1536-1539
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Primary Chemical Reactions Induced by Transformation of Radioactive Nuclei in Solids at Low Temperatures. Investigation by Means of the Emission Mössbauer and Positron Spectroscopies
    Autorzy:
    Byakov, V. M.
    Kulikov, L. A.
    Perfil'ev, Y. D.
    Stepanov, S. V.
    Powiązania:
    https://bibliotekanauki.pl/articles/2043320.pdf
    Data publikacji:
    2005-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.80.Fe
    36.10.Dr
    78.70.Bj
    Opis:
    A set of early chemical reactions in grapes of ionization (blobs) arising in tracks of fast electrons and positrons in liquids as well as formed by the Auger electrons in frozen aqueous media around decaying Mössbauer $\text{}^{57}$Co or $\text{}^{119m}$Sn nuclei is suggested. The mechanism predicts a correlated variation of the formation probabilities of intrablob final products, namely Fe$\text{}^{2+}$-Fe$\text{}^{3+}$ or Sn$\text{}^{2+}$-Sn$\text{}^{4+}$ ions, positronium atom and molecular hydrogen with variation of temperature, degree of crystallinity, concentration of electron scavengers. These correlations indicate on similarity of chemical processes as in blobs created by $\text{}^{57}$Co and $\text{}^{119m}$Sn after their decay as well as in blobs produced in tracks of fast positrons and electrons.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 5; 792-798
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-12 z 12

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