ISO/TS 23878:2024

This document describes a method for performing positron annihilation lifetime measurements using a 22Na 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.