Nanotechnologies. Positron annihilation lifetime measurement for nanopore evaluation in materials
Nanotechnologies. Positron annihilation lifetime measurement for nanopore evaluation in materials
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1 Scope This document describes a method for performing positron annihilation lifetime measurements using a 22 Na positron source that decays with β + emission. The β + (positron) lifetime is determined from a measurement of the lifetime of the ortho - positronium which ranges from 1 ns to 10 ns (ascribed to a pore size from approximately 0,3 nm to 1,3 nm in diameter), as observed for polymeric materials in which the positronium atoms mostly annihilate via a two-gamma annihilation process. This document is not applicable to thin surface layers (that are less than several micrometers). This document does not apply to measuring: — non- positronium forming materials; — positronium -forming materials that induce a spin conversion reaction; — positronium -forming materials that contain chemicals influencing the annihilation process of ortho - positronium by chemical reactions; — positronium -forming materials that contain mesoporous silica gels with a large contribution from the three-gamma annihilation process.
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