Positron diffusion in solid and liquid metals.
Item
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Title
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Positron diffusion in solid and liquid metals.
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Identifier
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AAI9224818
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identifier
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9224818
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Creator
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Gramsch, Ernesto Vicente.
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Contributor
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Adviser: Kelvin G. Lynn
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter
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Abstract
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A systematic study of diffusion of positrons in several liquid and solid metals was performed with a vertical positron beam. The S parameter and positronium fraction was measured as a function of temperature in the solid and liquid phases for Ga, Bi, Na, Sn, In and Pb. An appreciable change is observed in metals where positrons trapping is not observed in the solid just below the melting point (Ga, Bi, Na, Sn). In metals where positrons are trapped below the melting point (In and Pb), a very small or no change is observed upon melting. The results suggest that all positrons are trapped in the liquid.;The diffusion length of positrons in the liquid was also measured. In Ga, Bi and Sn, a large drop is observed upon melting. In Pb and In only small or no change is observed. In all liquid metals, as the temperature of the liquid is increased the diffusion length increases. Diffusion appears to be related to trapping in temporary density fluctuations, thus the positron hops from one trap to another. The size of the traps is strongly dependent on temperature, so that when it is increased, the hopping motion increases.;The re-emitted energy spectra of positrons from the liquid and solid surfaces was measured. No appreciable change was seen with increasing temperature, or when the sample is melted.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
