Nanotechnologies — Positron annihilation lifetime measurement for nanopore evaluation in materials

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.

Nanotechnologies – Mesure d'annihilation de la durée de vie de positrons pour l'évaluation de nanopores dans des matériaux

General Information

Status
Published
Publication Date
15-Aug-2024
Current Stage
6060 - International Standard published
Start Date
16-Aug-2024
Due Date
21-Jul-2024
Completion Date
16-Aug-2024
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Technical specification
ISO/TS 23878:2024 - Nanotechnologies — Positron annihilation lifetime measurement for nanopore evaluation in materials Released:16. 08. 2024
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Technical
Specification
ISO/TS 23878
First edition
Nanotechnologies — Positron
2024-08
annihilation lifetime measurement
for nanopore evaluation in
materials
Nanotechnologies – Mesure d'annihilation de la durée de vie de
positrons pour l'évaluation de nanopores dans des matériaux
Reference number
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General .1
3.2 Experimental set-up .2
4 Symbols and abbreviated terms. 2
5 Principle . 3
6 Overview of the positron annihilation lifetime measurement . 4
7 Apparatus . 7
7.1 Specification of the detector .7
7.2 Discrimination of the detected signals .8
7.3 Measurement conditions .8
8 Preparation of the positron source. 9
9 Preparation of the measurement specimen . 9
10 Data analysis . 9
11 Reporting .10
11.1 Specific values .10
11.2 Pore dimension.11
12 Reference materials .11
Annex A (informative) Interlaboratory comparison .12
Annex B (informative) Configuration of the apparatus .15
Annex C (informative) List of parameters and measurement conditions . 19
Bibliography .21

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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This document was prepared by Technical Committee ISO/TC 229, Nanotechnologies.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
This document describes a method for measuring and reporting the lifetime of ortho-positronium utilizing
the positron annihilation lifetime technique. Some of the positrons introduced into insulating materials, like
oxides and organic polymers, can form the spin parallel positron-electron bound state ortho-positronium,
which tends to localize in voids. In its trapped state, ortho-positronium annihilates with a lifetime that is
less than its intrinsic lifetime of 142 ns in vacuum via a two-gamma annihilation process, where this lifetime
component is well correlated with the void dimension. Based on this principle, one can evaluate the average
porosity originating from nanometer size voids, such as free volumes in polymers. It is well documented that
the positron annihilation lifetime technique is a powerful tool for characterizing the nanopores of various
functional materials. Increased demands on the reliable evaluation of nanopores using this technique have
emerged for various industrial applications.
This document describes a method for performing positron annihilation lifetime measurements to analyse
the lifetime of the ortho-positronium ranging from 1 ns to 10 ns (ascribed to a pore size from approximately
0,3 nm to 1,3 nm in diameter), observed for polymeric materials. It also contains measurement procedures,
data analysis, and reporting sections. In the annexes, the results of an interlaboratory comparison using
two types of reference materials conducted by eight participating institutions, are described, followed by
details of measurement systems that are based on the available analogue and digital methods, and a list of
parameters and measurement conditions provided as a guide to the user.

v
Technical Specification ISO/TS 23878:2024(en)
Nanotechnologies — Positron annihilation lifetime
measurement for nanopore evaluation in materials
1 Scope
This document describes a method for performing positron annihilation lifetime measurements using a 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.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org
3.1 General
3.1.1
positronium
bound state of a positron and an electron
3.1.2
positron lifetime
component lifetime corresponding to the annihilation of a large number of positrons or positroniums, and
extracted from a measured lifetime spectrum

3.2 Experimental set-up
3.2.1
scintillator
material that luminesces when excited by radiation, wherein the luminescent energy is related to the energy
deposited by the injected radiation
3.2.2
photomultiplier tube
vacuum phototube that converts incident light to an electronic signal, the magnitude of which is based on the
energy and number of the incident photons, and subsequently amplifies that signal to provide an electrical output
3.2.3
counting rate
measured number of events per unit time where an event is the coincident detection of the photons generated
during the production and annihilation of positrons
3.2.4
positron source
+
emitter of positrons due to nuclear transmutation via β decay
22 22
Note 1 to entry: Sodium-22 ( Na) transmuting to Ne is a positron source, for example.
3.2.5
amplifier
module that increases the amplitude of a signal
3.2.6
gate and delay generator
module that generates a logic pulse of a desired duration (gate width) and with the desired delay relative to
a reference event
4 Symbols and abbreviated terms
ADC analogue-to-digital converter
CFDD constant fraction differential discriminator
CRM certified reference material
DCFD differential constant fraction discriminator
GDG gate and delay generator
I relative intensity of lifetime component
LLD lower level discriminator
MCA multichannel analyzer
NIM nuclear instrument modules
PMT photomultiplier tube
Ps positronium
RI radioisotope
TAC time-to-amplitude converter

ULD upper level discriminator
o-Ps ortho-positronium (triplet state)
p-Ps para-positronium (singlet state)
τ positron or positronium component lifetime extracted from the measured lifetime spectrum
Na sodium with an atomic mass number of 22
Ne neon with an atomic mass number of 22
Ne* excited state of neon with an atomic mass number of 22
5 Principle
A fraction of the total number of positrons injected into an insulating polymer, such as polyolefins, can form
positronium (P
...

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