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Positron Irradiation Effects on Positronium Formation in Polycarbonate Sduring a Positron-Annihilation Experiment

100%
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.
2
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Application of Coincidence Doppler Broadening Spectroscopy to Hydrocarbons at Different Substance States

76%
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.
3
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Application of a Pulsed Slow-Positron Beam to Low-Density Polyethylene Film

64%
Hamada E., Oshima N., Katoh K., Suzuki T., Kobayashi H., Kondo K., Kanazawa I., Ito Y.
Acta Physica Polonica A
|
2001
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vol. 99
|
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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