Development of an ISO technical specification for evaluation of pore size in materials via the positron annihilation lifetime technique

Abstract

We have developed a Technical Specification (TS) under the International Organization for Standardization (ISO) for the evaluation of pore size in materials via the positron annihilation lifetime technique (ISO/TS 23878:2024). This TS outlines a standard procedure for measuring the ortho-positronium (o-Ps) lifetime in Ps-forming materials, employing a conventional sandwich configuration with two γ-ray photon detectors. The TS describes the measurement procedure, data analysis, and conversion from measured o-Ps lifetime to nanopore size via the Tao-Eldrup formula, largely based on a previous Japanese domestic standard (JIS TS Z 0031:2012). To ensure the validity of measurement and data analysis procedures, an inter-laboratory comparison involving eight institutions was conducted using two types of reference materials: fused silica and polymethyl methacrylate.