Intrinsic momentum distributions of positron and positronium annihilation in polymers

Sato, K.; Ito, Kenji; Hirata, Koichi; Yu, Ruan; Kobayashi, Yoshinori

doi:10.1103/physrevb.71.012201

Cited by 68 publications

(86 citation statements)

References 11 publications

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“…This paper concerns the application of positron annihilation techniques to identify the effects of polar groups with a dipole distribution of electric charge in polymer chains and the extent to which those effects may be modified in polymer blends [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Influence of polar groups in binary polymer blends on positronium formation

et al. 2013

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The present work studied the role of the polar group unconjugated oxygen on the inhibition of positronium (Ps) formation in two binary blends made from a set of chosen constituent polymers with polar and weakly polar groups (nonpolar). The polymer blend samples of PVC-EVA and PVC-SAN were investigated by coincidence Doppler broadening and positron lifetime techniques. The strong polar acetate group in the EVA contributed to positron annihilation with electrons of unconjugated oxygen (-C + =O − ) as revealed by the momentum distribution curves peaking around 17 P L (10 −3 m 0 c). The ortho-Ps intensity indicated the unconjugated oxygen shows about a 28% Ps reduction even in the presence of a strong Ps inhibiting halogen (Cl − ). In contrast, this effect was not seen in the PVC-SAN blends since SAN contains a weakly polar (nonpolar) acrylonitrile group (C≡N). Our results indicate the chlorine of PVC in the blends is a major contributor to Ps inhibition through the formation of a (Cl − -e +) bound state but the unconjugated oxygen in EVA of the PVC-EVA blend also plays a similar, but lesser, role.

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Section: Introductionmentioning

confidence: 99%

Influence of polar groups in binary polymer blends on positronium formation

et al. 2013

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“…A correlation between Doppler broadening line-shape S parameter and ortho-positronium fraction, I 3 (S−I 3 correlation) [5] has been introduced to examine intrinsic momentum distributions of positrons (e + ), para-positronium (p-Ps), and orthopositronium (o-Ps). The correlation has been found to be classified into the following groups depending on the chemical element which polymers contain: (1) polymers consisting of only carbon and hydrogen, (2) oxygen-containing polymers, and (3) fluorine-containing polymers [3]. In addition, low energy Ps formed by recombination of weakly bound Mott-Wannier (MW) positron-electron pairs with large separations becomes visible by the S−I 3 correlation [4].…”

Section: Introductionmentioning

confidence: 99%

“…We have systematically investigated Ps formation in polymers by employing coincident Doppler broadening and positron lifetime spectroscopy [3,4]. A correlation between Doppler broadening line-shape S parameter and ortho-positronium fraction, I 3 (S−I 3 correlation) [5] has been introduced to examine intrinsic momentum distributions of positrons (e + ), para-positronium (p-Ps), and orthopositronium (o-Ps).…”

Section: Introductionmentioning

confidence: 99%

Positron and Positronium Annihilation in Polymers Studied by Age-Momentum Correlation Spectroscopy

et al. 2008

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Positron (e + ) and positronium (Ps) annihilation processes in polymers are studied by positron age-momentum correlation spectroscopy, which can sensitively probe momentum distributions of e + , p-Ps, and o-Ps. For polyether sulfone and ethylene tetrafluoroethylene copolymer belonging to oxygen-containing polymers (O group) and fluorine-containing polymers (F group), respectively, significant effects of positron trapping by polar element are observed. The Doppler profile of o-Ps pick-off annihilation is strongly influenced by F atoms, giving rise to anomalous broadening. The results are discussed together with our previous data of the S−I 3 correlation in order to explore the feasibility of chemical analysis around the free volumes by age-momentum correlation spectroscopy.

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“…Measurements of the Doppler shifts by γ-ray energy spectroscopy with high purity Ge detector make it possible to obtain information on the momentum distribution of the positron-electron annihilation pairs. The momentum distribution of o-Ps is broadened centered at 511 keV because the pick-off annihilation is influenced by electrons bound to the surrounding molecules [22]- [23]. Thus, the momentum distribution of o-Ps pick-off annihilation provides the information on electronic states of pore surfaces.…”

Section: Introductionmentioning

confidence: 99%