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Digitale Medien

Positron decay in polymers: Molecular weight dependence in polystyrene (1975)

West, D. H. D. ; McBrierty, V. J. ; Delaney, C. F. G.

Springer

Applied physics 7 (1975), S. 171-174

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ISSN: 1432-0630

Schlagwort(e): Positron annihilation ; Polymers

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract The decay time τl ofo-Ps by the electron pickoff process has been measured in polystyrene as a function of molecular weight. For samples below their glass transition temperature τl is essentially independent of $$\bar M_n $$ . In the low molecular weight region, $$\bar M_n〈 850$$ , τl increased with decreasing $$\bar M_n $$ in line with earlier theoretical predictions. The overall behaviour reflects closely the dependence of free volume on $$\bar M_n $$ . The effects of molecular motion on τl are examined and it is concluded that the decay time is insensitive to such motions in polystyrene below the melting point, in contrast to what is observed in polytetrafluoroethylene.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00936020

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Digitale Medien

First measurements of positronium total scattering cross sections (1975)

Spektor, D. M. ; Paul, D. A. L.

Springer

Applied physics 5 (1975), S. 383-384

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ISSN: 1432-0630

Schlagwort(e): Positron annihilation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract A new type of experiment has been devised in which ortho-positronium diffusion to the metal walls of a series of parallel-sided cells is studied by measuring the annihilation lifetimes. Experimental results are subjected to an analysis in which two parameters are varied to give a best fit, one of the two parameters being the scattering cross section. The method requires a number of systematic corrections which have still to be worked out. Preliminary cross section values for helium, argon and isobutane are 0.017 πa 0 2 , 0.09 πa 0 2 , and 0.54 πa 0 2 , respectively.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00928029

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Digitale Medien

Positron annihilation in ionic crystals (1975)

Balogh, Á. ; Dézsi, I. ; Horváth, D. ; [weitere]

Springer

Applied physics 6 (1975), S. 21-23

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ISSN: 1432-0630

Schlagwort(e): Positron annihilation ; Ionic crystals

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau , Physik

Notizen: Abstract Positron lifetime measurements were made on Ca2+ doped NaCl, Ba2+ doped NaCl and X-ray- and additively-coloured KCl crystals. In the NaCl(Ca) system a correlation which could be approximated by a power equation was found between the dopant concentration and the positron annihilation parameters. In the NaCl(Ba) system the decay parameters do not change significantly as expected and no significant difference in the decay parameters of the coloured and uncoloured crystals could be found.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00883544

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