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1
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Relationship between Enhanced Positronium Formation and Enhanced Positron Trapping in Polymers at Low Temperature

100%
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.
2
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Positron Irradiation Effects on Positronium Formation in Polycarbonate Sduring a Positron-Annihilation Experiment

81%
Suzuki T., Kondo K., Hamada E., Ito Y.
Acta Physica Polonica A
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2001
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vol. 99
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issue 3-4
515-521
EN
The positron-irradiation effect on polycarbonate during a positron-annihilation lifetime spectroscopy experiment was investigated using different intensities of ^{22}Na positron sources andγ-irradiated samples. The decrease in I_3 was larger for a larger intensity of positron sources. In the case of a weak source (≈ 140 kBq), I_3 did not change with the elapsed time for non-irradiated samples. However, for 1 MGy irradiated samples, I_3 measured with the weak source increased with the elapsed time. This can be attributed to a decrease in the radicals induced in the irradiated samples by γ-irradiation. In order to explain the change in I_3 measured at room and liquid-nitrogen temperatures, several effects, such as radicals, cross-linking, structure change, and charging, need to be considered. Also, it is difficult to explain the change in I_3 using only one of these effects.
3
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Polymerization of Epoxy Resins Studied by Positron Annihilation

81%
Suzuki T., Hayashi T., Ito Y.
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vol. 95
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issue 4
671-676
EN
The polymerization process of epoxy resins (bisphenol-A dicyanate) was studied using positron-annihilation lifetime spectroscopy. The polymerization from monomer to polymer through a polymerization reaction was followed by positron-annihilation lifetime spectroscopy measurements. Resins kept at curing temperatures (120, 150, and 200°C) changed form from a powder to a solid through a liquid. The size of the intermolecular spaces of the solid samples increased along with the progress of polymerization.
4
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Growth Spirals Appeared in c-Axis Oriented YBCO Films Grown on MgO Substrate by Sputtering

81%
Suzuki T., Azechi K., Sakurai S., Aizawa S.
Acta Physica Polonica A
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1997
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vol. 92
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issue 1
215-220
EN
The early stages of growth and the evolution of surface microstructure of epitaxial c-axis YBa_{2}Cu_{3}O_{7-x} thin films were studied as a function of film thickness, growth temperature, and growth rate. The films were grown in situ on as-polished or annealed MgO(100) substrates by off-axis magnetron sputtering. Atomic force microscopy was used to observe the surface microstructure. From the results at early stages, we proposed a growth model of spirals for the films grown on as-polished substrate, i.e. spirals are formed around the surface roughness of the substrate. Growth temperature and growth rate dependence on the density of spirals support this model. That is, the density of spirals does not change according to the change of growth temperature (600-740°C) or growth rate (7-80 nm/h).
5
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The Effect of Visible Light Irradiation on Positronium Formation in Polyethylene at Low Temperature

71%
Ito Y., Hirade T., Hamada E., Suzuki T., Ito Y.
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vol. 95
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issue 4
533-538
EN
The effect of visible light exposing on the ortho-positronium formation in polyethylene was studied. Lifetime spectra of positrons in polyethylene were measured in the temperature range between 50 K and 370 K. It was observed that the visible light quenches the enhancement of ortho-positronium intensity (I_{3}) at lower temperature than ca. 250 K - the glass transition temperature of polyethylene. On the other hand, the lifetime of ortho-positronium component (τ_{3}) was not affected by the presence of the visible light.
6
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Application of Coincidence Doppler Broadening Spectroscopy to Hydrocarbons at Different Substance States

61%
Yu R., Suzuki T., Ito Y., Djourelov N., Kondo K., Shantarovich V.
Acta Physica Polonica A
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2005
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vol. 107
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issue 4
697-701
EN
Coincidence Doppler broadening spectroscopy was applied to study n-hexane (C_6H_{14}), cyclohexane (C_6H_{12}) and cyclohexanone (C_6H_{10}O), at solid, as well as liquid states. The experiments were performed in parallel with traditional positron annihilation lifetime spectroscopy. Significant positron trapping by oxygen was observed in cyclohexanone; the oxygen effect is stronger in liquid state than in solid one, which can possibly be attributed to positron solvation in polar solution. Coincidence Doppler broadening results for n-hexane and cyclohexane indicate an existence of higher energetic annihilation electrons in Ps-bubble forming liquids than that in solids.
7
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Some Aspects of Free Volume Studies in Molecular Substances Using Positron Annihilation Experiments

61%
Shantarovich V., Suzuki T., Djourelov N., Shimazu A., Gustov V., Kevdina I.
Acta Physica Polonica A
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2005
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vol. 107
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issue 4
629-634
EN
Positron annihilation lifetime spectroscopy is accepted now as a method for the studies of elementary free volumes (free volume holes) in solids, in polymers in particular. The aim of this paper is to discuss some problems, the difficulties on the way of this application and to illustrate them by several examples obtained by the authors.
8
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Application of a Pulsed Slow-Positron Beam to Low-Density Polyethylene Film

52%
Hamada E., Oshima N., Katoh K., Suzuki T., Kobayashi H., Kondo K., Kanazawa I., Ito Y.
Acta Physica Polonica A
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2001
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vol. 99
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issue 3-4
373-378
EN
A pulsing system for a slow-positron beam was applied to study the region near the surface of low-density polyethylene film using positron-annihilation lifetime measurement. The lifetime and intensity of ortho-positronium near the surface were measured as a function of the incident positron energy (1.6-9.1 keV). The size of intermolecular spaces in the surface region (~ 1500 nm) was larger than that in the bulk region. This tendency was especially strong in the region around 200 nm below the surface. On the other hand, the intensity of ortho-positronium decreased at lower incident positron energies, which was attributed to a decrease in the density of the spur electrons and/or an increase in the number of reemitted positrons from the surface.
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