SIST EN ISO 8529-1:2023

Neutron reference radiations fields - Part 1: Characteristics and methods of production (ISO 8529-1:2021)

This document specifies the neutron reference radiation fields, in the energy range from thermal up to 20 MeV, for calibrating neutron-measuring devices used for radiation protection purposes and for determining their response as a function of neutron energy.
This document is concerned only with the methods of producing and characterizing the neutron reference radiation fields. The procedures for applying these radiation fields for calibrations are described in References [1] and [2].
The neutron reference radiation fields specified are the following:
—    neutron fields from radionuclide sources, including neutron fields from sources in a moderator;
—    neutron fields produced by nuclear reactions with charged particles from accelerators;
—    neutron fields from reactors.
In view of the methods of production and use of them, these neutron reference radiation fields are divided, for the purposes of this document, into the following three separate clauses:
—    In Clause 4, radionuclide neutron sources with wide spectra are specified for the calibration of neutron-measuring devices. These sources should be used by laboratories engaged in the routine calibration of neutron-measuring devices, the particular design of which has already been type tested.
—    In Clause 5, accelerator-produced monoenergetic neutrons and reactor-produced neutrons with wide or quasi monoenergetic spectra are specified for determining the response of neutron‑measuring devices as a function of neutron energy. Since these neutron reference radiation fields are produced at specialized and well-equipped laboratories, only the minimum of experimental detail is given.
—    In Clause 6, thermal neutron fields are specified. These fields can be produced by moderated radionuclide sources, accelerators, or reactors.

Neutronen-Referenzstrahlungsfelder - Teil 1: Charakteristika und Verfahren zur Erzeugung (ISO 8529-1:2021)

Dieses Dokument legt die Neutronen-Referenzstrahlungsfelder im Energiebereich von thermisch bis 20 MeV fest, die zur Kalibrierung von Neutronenmessgeräten für Strahlenschutzzwecke und zur Bestimmung ihres Ansprechvermögens in Abhängigkeit von der Neutronenenergie verwendet werden.
Dieses Dokument befasst sich nur mit den Verfahren zur Erzeugung und Charakterisierung der Neutronen-Referenzstrahlungsfelder. Die Verfahren zur Anwendung dieser Strahlungsfelder für Kalibrierungen sind in den Literaturhinweisen [1] und [2] beschrieben.
Die beschriebenen Neutronen-Referenzstrahlungsfelder sind:
–   Neutronenfelder von Radionuklidquellen, einschließlich Neutronenfelder von Quellen in einem Moderator;
–   Neutronenfelder, die durch Kernreaktionen mit geladenen Teilchen aus Beschleunigern erzeugt werden;
–   Neutronenfelder von Reaktoren.
Auf Grundlage ihrer Erzeugungs- und Anwendungsverfahren werden diese Neutronen-Referenzstrahlungsfel¬der für die Zwecke dieses Dokuments in den folgenden drei Abschnitten behandeltN1.
–   In Abschnitt 4 werden Radionuklid-Neutronenquellen mit breiten Spektren für die Kalibrierung von Neutro¬nenmessgeräten beschrieben. Diese Quellen sollten von Laboren verwendet werden, die sich mit der regelmäßigen Kalibrierung von Neutronenmessgeräten befassen, deren jeweilige Konstruktionsart bereits bauartgeprüft ist.
–   In Abschnitt 5 werden beschleunigererzeugte monoenergetische Neutronen und reaktorerzeugte Neutro¬nen mit breiten oder quasi-monoenergetischen Spektren zur Bestimmung des Ansprechvermögens von Neutronenmessgeräten in Abhängigkeit von der Neutronenenergie beschrieben. Da diese Neutronen-Referenzstrahlungsfelder in spezialisierten und gut ausgestatteten Laboren erzeugt werden, wird nur ein Minimum an experimentellen Details angegeben.
–   In Abschnitt 6 werden thermische Neutronenfelder beschrieben. Diese Felder können durch moderierte Radionuklidquellen, Beschleuniger oder Reaktoren erzeugt werden.

Champs de rayonnement neutronique de référence - Partie 1: Caractéristiques et méthodes de production (ISO 8529-1:2021)

Le présent document spécifie les champs neutroniques de référence, s’inscrivant dans le domaine d’énergie allant des «thermiques» jusqu’à 20 MeV, destinés à l’étalonnage des dispositifs de mesure des neutrons utilisés à des fins de radioprotection et pour déterminer leur réponse en fonction de l’énergie des neutrons.
Le présent document traite uniquement des méthodes de production et de caractérisation des champs de rayonnement neutronique de référence. Les modes opératoires d’application de ces champs de rayonnement à des fins d’étalonnage sont décrits dans les références [1] et [2].
Les champs de rayonnement neutronique de référence spécifiés sont:
—    les champs de neutrons issus de sources de radionucléides, y compris les champs de neutrons de sources placées dans un modérateur;
—    les champs de neutrons produits par réactions nucléaires avec des particules chargées issues d’accélérateurs;
—    les champs de neutrons issus de réacteurs.
Compte tenu des méthodes de production et de leur utilisation, ces champs de rayonnement neutronique de référence sont, pour les besoins du présent document, traités dans les trois articles distincts suivants:
—    l’Article 4 spécifie les sources de neutrons de radionucléides à spectre large destinées à l’étalonnage de dispositifs de mesure des neutrons. Il convient que ces sources soient utilisées par des laboratoires chargés de l’étalonnage de routine des dispositifs de mesure des neutrons dont la conception particulière a déjà fait l’objet d’un essai de type;
—    l’Article 5 spécifie les neutrons monoénergétiques produits par des accélérateurs et les neutrons produits dans des réacteurs à spectre large ou quasi monoénergétiques, destinés à déterminer la réponse de dispositifs de mesure des neutrons en fonction de l’énergie des neutrons. Ces champs de rayonnement neutronique de référence étant produits dans des laboratoires spécialisés et bien équipés, seul un minimum de détails expérimentaux est donné;
—    l’Article 6 spécifie les champs neutroniques thermiques qui peuvent être produits par des sources de radionucléides modérées, des accélérateurs ou des réacteurs.

Referenčna polja nevtronskih sevanj - 1. del: Značilnosti in metode izdelave (ISO 8529-1:2021)

Ta dokument določa referenčna polja nevtronskih sevanj v energijskem območju od toplotnega do 20 MeV za umerjanje nevtronskih merilnikov, ki se uporabljajo za zaščito pred sevanjem in za ugotavljanje njihovega odziva glede na energijo nevtronov.
Ta dokument se nanaša le na metode izdelave in karakterizacije referenčnih polj nevtronskih sevanj.
Določa naslednja referenčna polja nevtronskih sevanj:
–   nevtronska polja iz virov radionuklidov, vključno z nevtronskimi polji iz virov v moderatorju;
–   nevtronska polja, ki nastanejo pri jedrskih reakcijah z nabitimi delci iz pospeševalnikov;
–   nevtronska polja iz reaktorjev.

General Information

• Status: Published
• Public Enquiry End Date: 13-Jun-2023
• Publication Date: 20-Aug-2023
• ICS: 17.240 - Radiation measurements
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 26-Jul-2023
• Due Date: 30-Sep-2023
• Completion Date: 21-Aug-2023
• Ref Project: EN ISO 8529-1:2023 - Neutron reference radiations fields - Part 1: Characteristics and methods of production (ISO 8529-1:2021)

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2023
Referenčna polja nevtronskih sevanj - 1. del: Značilnosti in metode izdelave (ISO
8529-1:2021)
Neutron reference radiations fields - Part 1: Characteristics and methods of production
(ISO 8529-1:2021)
Champs de rayonnement neutronique de référence - Partie 1: Caractéristiques et
méthodes de production (ISO 8529-1:2021)
Ta slovenski standard je istoveten z: EN ISO 8529-1:2023
ICS:
17.240 Merjenje sevanja Radiation measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 8529-1
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2023
EUROPÄISCHE NORM
ICS 17.240
English Version
Neutron reference radiations fields - Part 1:
Characteristics and methods of production (ISO 8529-
1:2021)
Champs de rayonnement neutronique de référence -
Partie 1: Caractéristiques et méthodes de production
(ISO 8529-1:2021)
This European Standard was approved by CEN on 16 July 2023.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8529-1:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 8529-1:2021 has been prepared by Technical Committee ISO/TC 85 "Nuclear energy,
nuclear technologies, and radiological protection” of the International Organization for Standardization
(ISO) and has been taken over as EN ISO 8529-1:2023 by Technical Committee CEN/TC 430 “Nuclear
energy, nuclear technologies, and radiological protection” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by January 2024, and conflicting national standards shall
be withdrawn at the latest by January 2024.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 8529-1:2021 has been approved by CEN as EN ISO 8529-1:2023 without any
modification.
INTERNATIONAL ISO
STANDARD 8529-1
Second edition
2021-11
Neutron reference radiations fields —
Part 1:
Characteristics and methods of
production
Champs de rayonnement neutronique de référence —
Partie 1: Caractéristiques et méthodes de production
Reference number
ISO 8529-1:2021(E)
ISO 8529-1:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 8529-1:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Broad spectrum neutron reference radiation fields produced with radionuclide
sources . 3
4.1 Overview . 3
4.2 Types of calibration sources . 3
4.3 Source shape and encapsulation . 4
4.4 Photon component of the neutron field . 4
4.5 Energy distribution of neutron source emission rate . 5
4.6 Neutron fluence rate produced by a source. 5
4.7 Determination of the neutron source emission rate. 6
4.8 Irradiation facility . 6
5 Reference fields for the determination of the response of neutron‑measuring
devices as a function of neutron energy . 7
5.1 Overview . 7
5.2 General properties . 7
5.3 Neutron reference radiation fields produced with particle accelerators . 8
5.3.1 General requirements . 8
5.3.2 Energy of charged particles . 8
5.3.3 Neutron spectrum . 9
5.3.4 Parasitic and scattered neutron background . 9
5.3.5 Neutron fluence measurement and monitoring . 10
5.4 Neutron reference radiation fields produced with reactors . 10
5.4.1 General requirements . 10
5.4.2 Production and monitoring . 10
6 Thermal neutron reference radiation fields .10
Annex A (informative) Tabular and graphical representation of the neutron spectra for
radionuclide sources .12
Annex B (normative) Energy distribution of the neutron emission rate for the Cf source .14
Annex C (informative) Characteristics of D O-moderated Cf sources .16
Annex D (informative) Characteristics of Am-Be sources .20
Annex E (informative) Angular source emission rate characteristics of radionuclide
neutron sources .24
Annex F (normative) Conventional thermal‑neutron fluence rate .27
Bibliography .28
iii
ISO 8529-1:2021(E)
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, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely 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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,
and radiological protection, Subcommittee SC 2, Radiation protection.
A list of all the parts in the ISO 8529 series can be found on the ISO website.
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
ISO 8529-1:2021(E)
Introduction
This is the first of a set of three International Standards concerning the calibration of dosemeters and
dose rate meters for neutron radiation for protection purposes. It describes the characteristics and
methods of production of the neutron reference radiation fields to be used for calibrations. ISO 8529-2
describes fundamentals related to the physical quantities characterizing the radiation field and
calibration procedures in general terms, with emphasis on active dose rate meters and the use of
radionuclide sources. ISO 8529-3 deals with dosemeters for area and individual monitoring, describing
the respective procedures for calibrating and determining the response in terms of the International
Commission on Radiation Units and Measurements (ICRU) operational quantities. Conversion
coefficients for converting neutron fluence into these operational quantities are provided in ISO 8529-3.
v
INTERNATIONAL STANDARD ISO 8529-1:2021(E)
Neutron reference radiations fields —
Part 1:
Characteristics and methods of production
1 Scope
This document specifies the neutron reference radiation fields, in the energy range from thermal up
to 20 MeV, for calibrating neutron-measuring devices used for radiation protection purposes and for
determining their response as a function of neutron energy.
This document is concerned only with the methods of producing and characterizing the neutron
reference radiation fields. The procedures for applying these radiation fields for calibrations are
described in References [1] and [2].
The neutron reference radiation fields specified are the following:
— neutron fields from radionuclide sources, including neutron fields from sources in a moderator;
— neutron fields produced by nuclear reactions with charged particles from accelerators;
— neutron fields from reactors.
In view of the methods of production and use of them, these neutron reference radiation fields are
divided, for the purposes of this document, into the following three separate clauses:
— In Clause 4, radionuclide neutron sources with wide spectra are specified for the calibration of
neutron-measuring devices. These sources should be used by laboratories engaged in the routine
calibration of neutron-measuring devices, the particular design of which has already been type
tested.
— In Clause 5, accelerator-produced monoenergetic neutrons and reactor-produced neutrons with wide
or quasi monoenergetic spectra are specified for determining the response of neutron-measuring
devices as a function of neutron energy. Since these neutron reference radiation fields are produced
at specialized and well-equipped laboratories, only the minimum of experimental detail is given.
— In Clause 6, thermal neutron fields are specified. These fields can be produced by moderated
radionuclide sources, accelerators, or reactors.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 29661, Reference radiation fields for radiation protection — Definitions and fundamental concepts
3 Terms and definitions
For the purposes of this document, the terms and definitions of ISO 29661 and the following apply:
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
ISO 8529-1:2021(E)
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
neutron emission rate of a neutron source
B
differential quotient of N with respect to time, where N is the number of neutrons being emitted from
the source, in all directions
dN
B=
dt
–1
Note 1 to entry: The unit of the neutron emission rate is s .
3.2
direction distribution of the neutron emission rate
angular distribution of the neutron emission rate
B
Ω
differential quotient of B with respect to solid angle, where Ω is a specific spatial direction
dB
B =
Ω
dΩ
–1 –1
Note 1 to entry: The unit of the direction distribution of the neutron emission rate is s sr .
3.3
energy distribution of the neutron emission rate
spectral neutron emission rate
B
E
differential quotient of B with respect to energy, where E is the neutron energy
dB
B =
E
dE
–1 –1 –1 –1
Note 1 to entry: The unit of the spectrum of neutron emission rate is s J ; a frequently used unit is s MeV .
Note 2 to entry: The terms “spectrum” and “energy distribution” are considered to be equivalent.
Note 3 to entry: The neutron source emission rate B is derived from B as follows:
E
∞
BB= dE
E
∫
Note 4 to entry: At a distance l from a point source, the energy distribution of the fluence rate φ , due to neutrons
E
emitted isotropically from the point source with a spectral neutron emission rate B (neglecting the influence of
E
the air and the surrounding material), is given by:
B
E
ϕ =
E
4πl
3.4
fluence‑averaged neutron energy
E
neutron energy averaged over the energy distribution of the fluence
∞
EE=⋅Φ EEd
()
E
∫
Φ
where Φ (E) is the energy distribution of the neutron fluence and Φ is the total fluence.
E
ISO 8529-1:2021(E)
4 Broad spectrum neutron reference radiation fields produced with
radionuclide sources
4.1 Overview
In this clause, neutron reference fields produced with radionuclide sources are specified, which are
particularly suited for the calibration of neutron-measuring devices (see Reference [2]).
Thermal neutron reference radiation fields are achievable by moderating radionuclide sources, but are
covered by Clause 6.
4.2 Types of calibration sources
The radionuclide sources given in Table 1 shall be used to produce neutron reference radiation fields.
The numerical values given in Table 1 are to be taken only as a guide to the prominent features of the
sources, since the properties of a specific source vary with the construction of the source, because of
scattering and absorption of neutron and gamma radiation, and with the isotopic impurities of the
radioactive material used. Hence details of the source encapsulation are specified (see 4.3), and the
method for determining the anisotropy of the neutron emission is specified (see Annex E).
252 252
Cf has a high specific neutron emission rate and Cf sources are therefore comparatively small.
Because of their short half-life of 2,647 years, they need regular replacement.
252 252
The D O-moderated Cf source is ideally composed of a point Cf source located in the centre of a
300 mm diameter heavy-water sphere, surrounded by
a) a 0,8 mm thick iron shell, and
b) a1 mm thick cadmium shell.
In practice, a number of designs have been developed in reference laboratories, being slightly different
in terms of construction details, such as the guide used to locate the source in the sphere centre, the
material used to contain the heavy water, and the structure used to suspend or hold the moderating
sphere. In addition, every moderating assembly has specific D O purity and Cf source capsule. The
experience of reference laboratories suggests that variability in the construction of D O-moderated
252 [3]
Cf sources results in non-negligible differences in the energy distribution of the neutron fluence .
Laboratories should characterize their D O-moderated Cf sources by simulations and spectral
measurements. The energy distribution of the neutron emission rate and spectrum-averaged quantities
of these fields should be checked through comparisons. A representative spectrum of the D O-
moderated Cf source was derived, for the purposes of this document, by Monte Carlo simulations.
In this model, 11,4 % of the source neutrons are absorbed in the moderating assembly. See Annex C for
details.
Am-Be (α,n) neutron sources include appropriate alloys, mixtures or compounds of americium, such
as a compressed mixture of americium oxide and beryllium as appropriate. See Annex D for details.
241 [4][5][6] [7][8]
In addition to the sources listed in Table 1, sources such as Am-B(α,n) , Pu-Li(α,n) ,
[8] 241 [6] 241 [9] 244 [10]
Pu-Be(α,n) , Am-F(α,n) , Am-Li(α,n) and Cm are also used but are not addressed
1)
specifically in this document .
238 239
1) Plutonium-based (α,n) sources may actually include more than one plutonium isotope, such as Pu, Pu,
240 241 242
Pu, Pu and Pu.
ISO 8529-1:2021(E)
Table 1 — Reference radionuclide sources for calibrating neutron‑measuring devices
Ratio of photon to neutron
Fluence‑averaged Specific source
Half‑life ambient‑dose‑equivalent
a b
energy emission rate
Source
c
rates
d –1 –1
a MeV s kg
Cf (D O moder-
2 15 e
2,647 0,57 2,1 × 10 <0,18
ated)
252 15 f
Cf 2,647 2,13 2,4 × 10 0,05
–1 –1
s Bq
Am-Be(α,n)
g
small source 4,17
–5 h
432,6 6 × 10 <0,035
large source 4,05
a
The reported values are calculated applying the definition of the fluence-averaged neutron energy given in 3.4 to the
spectra tabulated in Annexes B, C and D.
b 252 241
For Cf sources, the specific emission rate is related to the mass of californium. For the Am-Be sources, this is
related to the Am activity and is subject to variations according to manufacturing process and degree of mixing. For
252 241
both Cf and Am-Be, these are indicative values only. For any source used to produce reference fields, a determination
of the neutron emission rate is needed. Information on the sources is given in References [3][11][12] for moderated Cf,
252 241
Reference [13] for Cf, and References [4][5][14][16] for Am-Be.
c
Calculated on the basis of the neutron spectra given in Annexes B, C and D and the conversion coefficients given in
Reference [17].
d 252 241
a = 1 mean solar year = 31 556 926 s or 365,242 20 days. Uncertainties on Cf and Am half-life can be assumed as
0,1 % (k=1) and 0,14 % (k=1) respectively. Half-life and related uncertainty are taken from Reference [18].
e
Data from References [12][19].
f 252
For approximately 2,5 mm thick steel encapsulation. The low energy gamma spectrum of Cf is easily shielded by
the small amount of steel in the encapsulation. Other construction details are likely to affect the ratio. Data for the photon
component of the Cf field are available in References [20][22].
g 241
For definition of "small" and "large" Am-Be source, see Annex D.
h
For sources enclosed within an additional 1 mm to 2 mm thick lead shield, see 4.4 for more information.
4.3 Source shape and encapsulation
The shape of the source would ideally be spherical, but most practical sources are cylindrical. In the
latter case, it is preferable that the diameter and length are approximately the same. The thickness of
the encapsulation should be uniform and small compared to the external diameter. For a Am-Be(α,n)
source, the spectral distribution, mainly in the energy range below approximately 2 MeV, depends, to
[5][15][16]
some extent, on the size and the composition of the source . See Annex D for more details.
[23]
Sources should comply with ISO 2919 encapsulation requirements .
4.4 Photon component of the neutron field
For Cf, the ratio of photon to neutron ambient dose equivalent rate is dependent upon the age of
the source because of the build-up of gamma-emitting fission products, as well as upon source
encapsulation. The 5 % value reported in Table 1 refers to new sources. During the first 30 years, this is
[21][22]
likely to remain below 10 % .
The Am-Be(α,n) source may be wrapped in a lead shield to reduce the gamma component. A thickness
[20][21][23]
of 1 mm to 2 mm reduces the photon to neutron dose-equivalent rate to less than 3,5 % . This
ratio does not depend on the americium activity and source encapsulation. The lead shield produces a
negligible change (less than 1 %) in the neutron dose equivalent rate. In the absence of the lead shield,
the photon to neutron dose equivalent rate (mainly from 59,5 keV gamma radiation) depends upon
[20]
the source construction. Based on bibliography data , it decreases as the physical size of the source
increases. Typical values for bare sources are 50 % for small sources (in the order of 37 GBq), 30 % and
20 % for larger sources (370 GBq and 555 GBq respectively).
ISO 8529-1:2021(E)
4.5 Energy distribution of neutron source emission rate
The tabular and graphical representation of neutron spectra in this document is addressed in Annex A.
The energy distribution reported in Annex B shall be used for Cf sources.
The spectrum of the D O-moderated Cf source is affected by the construction details of the
moderating sphere, D O purity, and any additional material surrounding the source. See Annex C for
details.
For Am-Be, sources with different capsules, americium activity, chemical composition, granularity of
the active material, and construction methods, result in slightly different spectra. This is discussed in
Annex D.
The average fluence to dose equivalent conversion coefficients, h can be derived from the spectra
Φ
using Formula (1):
∞
hh= ()EEΦ d (1)
ΦΦ E
∫
Φ
where Φ is taken to be proportional to B and h (E) is the energy-dependent fluence to dose equivalent
E E Φ
conversion coefficient from Reference [17].
4.6 Neutron fluence rate produced by a source
The fluence rate produced by a neutron source is determined primarily from its neutron emission rate,
B, and the distance between the source centre and the point of test. Neutron sources generally show
anisotropic neutron emission in a coordinate system fixed in the geometrical centre of the source. The
coordinate system is shown in Figure 1.
The neutron emission rate, B, and its direction distribution, dB/dΩ, in the direction used for calibrations,
shall be determined (see also Annex E).
[24]
For the purposes of determining the direction distribution , the measuring device should have the
smallest solid angle consistent with deriving good statistics and should have sufficiently small energy
dependence of the fluence response to avoid sensitivity to changes of the energy with the angle.
Anisotropy measurements should be corrected for the contribution of scattered neutrons.
Once this is done, the neutron fluence rate, at a distance, l, from the centre of the source in a direction
for which θ = 90°, may then be taken as per Formula (2):
dB 1
ϕ =× (2)
()l,90°
dΩ
l
The neutron fluence rate obtained from this expression still has to be corrected for air attenuation,
and scattering from air and the surrounding material. These corrections, which are only negligible in
exceptional circumstances, are described in detail in Reference [1].
ISO 8529-1:2021(E)
Figure 1 — Coordinate system for the case of an anisotropically emitting source
4.7 Determination of the neutron source emission rate
241 252
The emission rate from Am-Be(α,n) and Cf sources shall be measured by a reference laboratory
before use. Reference laboratories can generally measure the emission rate of neutron sources to within
[25]
a relative standard uncertainty of about 1,5 % (k=1) .
For Am-Be(α,n) sources there is the possibility that, with time, the constituent components may shift
with respect to each other, with a resultant change in the neutron source emission rate.
The source emission rate of a Cf source shall be corrected for radioactive decay on a day-to-day
basis. It is important to take into account the decay of all the constituents of the source including the
250 254 248 252 [26]
Cf, Cf, and Cm in available Cf sources . Therefore, the manufacturer shall supply a dated
certificate of the isotopic composition and a record of when the curium was last removed from the
source material.
It is recommended that the emission rate of neutron sources be checked every five years. An alternative
to recalibrating the sources in a manganese sulphate bath is to perform regular stability tests against
stable instruments or against other sources.
252 250
For Cf sources expected to have more than 5 % neutron emission due to the combination of Cf and
Cm, these tests should take place more frequently.
4.8 Irradiation facility
In general, irradiation rooms have thick walls (for example concrete) for shielding. In this case, the inside
dimensions should be as large as practically possible. The magnitude of the correction for room- and air-
scattered neutrons, and the resulting uncertainty in the field quantities, depend critically on the size of
the room. In all cases, the effects of scattered neutrons may be characterized through measurements
with a shadow cone and investigations of deviations from the 1/l -relationship (where l is the distance
between the neutron source and the detector reference point). Details of the recommended calibration
procedures are dealt with in Reference [1].
ISO 8529-1:2021(E)
5 Reference fields for the determination of the response of neutron‑measuring
devices as a function of neutron energy
5.1 Overview
In this clause, neutron reference radiation fields produced by particle accelerators and nuclear reactors
are specified. Those with nearly-monoenergetic spectra may be especially suited for the determination
of the response of neutron-measuring devices as a function of neutron energy. These fields may also
be used to determine dose equivalent rate dependence and directional dependence. Radiation fields
specified in this clause may also be used for the calibration of neutron-measuring devices.
Thermal neutron fields are achievable at reactors and by moderating neutrons from particle accelerators
or radionuclide neutron sources, but are covered by Clause 6.
5.2 General properties
The recommended neutron energies and the methods used for their production are given in Table 2,
along with relevant references. These energies were chosen for practical reasons, including yield, even
spacing in logarithmic energy scale, and availability of data from international comparisons. Some of
them were chosen because they can be produced in multiple ways (see for example 0,024 MeV).
Other energies can be used, provided they are well characterized. Methods to produce these energies
and to characterize the fields can be found in References [27] and [28].
With accelerators, the neutron energy range between 2 keV and 19 MeV can be covered in principle
using protons and deuterons up to 3,5 MeV, except for the gap region (6 MeV to 13 MeV).
Production of monoenergetic neutrons at 0° is usually advantageous because it shows a maximum in
the yield and a minimum in the variation of the energy and the yield with the angle. But angles larger
[29]
than 0° can be also used , provided that account is taken of specific problems, such as the larger
contribution of scattering in the target assembly, the strong variation of yield and energy with angle,
and the increased relative photon contribution.
Table 2 — Neutron radiations for determining the response of neutron‑measuring devices as a
function of neutron energy
Neutron energy References
Method of production
MeV (see Bibliography)
0,002 Scandium-filtered reactor neutron beam or accelerator-pro-
[30]
45 45
duced neutrons from reaction Sc(p,n) Ti
45 45 [31]
0,008 Accelerator-produced neutrons from reaction Sc(p,n) Ti
a
0,024 Iron/aluminium-filtered reactor neutron beam or acceler-
45 45 [29][32]
ator-produced neutrons from reactions Sc(p,n) Ti and
7 7
Li(p,n) Be.
45 45
Sc(p,n) Ti can generate both 0,024 and 0,027 MeV varying
the angle.
[33]
0,022 8 MeV neutrons can also be produced using a Sb-
Be(γ,n) radionuclide source
a
0,144 Silicon-filtered reactor neutron beam or accelerator-produced
[30][34][35]
3 7 7
neutrons from reactions T(p,n) He and Li(p,n) Be
ISO 8529-1:2021(E)
Table 2 (continued)
Neutron energy References
Method of production
MeV (see Bibliography)
a 3
0,25 Accelerator-produced neutrons from reaction T(p,n) He and
}
7 7
Li(p,n) Be
}
a 3
0,565 Accelerator-produced neutrons from reaction T(p,n) He and
}
7 7
Li(p,n) Be
a 3
}
1,2 Accelerator-produced neutrons from reaction T(p,n) He
a 3
}
2,5 Accelerator-produced neutrons from reaction T(p,n) He
ab 3
[22][23]
2,8 Accelerator-produced neutrons from reaction D(d,n) He
}
a 3
5,0 Accelerator-produced neutrons from reaction D(d,n) He
}
ab 4
14,8 Accelerator-produced neutrons from reaction T(d,n) He
}
17,0 Accelerator-produced neutrons from reaction T(d,n) He
}
c 4
19,0 Accelerator-produced neutrons from reaction T(d,n) He
}
a [36][38]
Energies at which international comparisons of neutron fluence measurements were performed .
b
Accelerator-produced neutrons, with deuteron energy up to a few hundred keV.
c
In the 17 MeV and 19 MeV fields parasitic neutrons are very likely to be present because of the high deuteron
energy used to produce this field. They need to be subtracted using a well-matched blank target. Such targets
are routinely available, and the time-of-flight technique should be used to check the equivalence of the targets. In
this way, the parasitic neutrons can be corrected for, and the fluence of the pure 17 MeV and 19 MeV neutron field
can be determined. Attention has to be made for those instruments under test that are also sensitive to parasitic
neutrons with energies lower than the main monoenergetic energy. In this case, a blank target measurement
might also be necessary.
5.3 Neutron reference radiation fields produced with particle accelerators
5.3.1 General requirements
An accelerator providing protons and deuterons up to an energy of 3,5 MeV is required to generate
neutrons of all the energies given in Table 2. For the production of neutrons with energies of 2,8 MeV
and 14,8 MeV, however, a small accelerator with a potential of up to few hundred kilovolts, is sufficient.
When these neutrons are used for calibrating instruments, the following parameters shall be assessed:
— charged particle beam energy;
— angle relative to the charged particle beam;
— neutron fluence measurements and monitoring;
— neutron spectrum;
— sources of scattered and contaminant neutrons;
— target age and thickness.
5.3.2 Energy of charged particles
Computer codes or databases are used to derive the charged particle energy required to obtain a given
[34][35]
neutron energy .
The energy of the incident charged particle beam shall be determined. A stabilised analysing magnet
calibrated by means of a few known nuclear reaction thresholds may be used in order to select the
momentum of the particle beam. The energy loss of the charged particles in the target shall be taken
into account in the calculation of the bombarding energy needed to produce the required neutron
ISO 8529-1:2021(E)
energy. Relevant stopping power values in different materials can be found in References [39][41]. A
computer code to calculate stopping power values can be found at www .srim .org.
5.3.3 Neutron spectrum
Due to energy losses in the target, and other influences, accelerated charged particles generate, at a
given angle, neutrons with a narrow, but finite, width in energy around the stated reference energy. For
[27]
thin targets , it is not necessary to consider this energy spread when applying the fluence-to-dose-
equivalent conversion coefficients in order to calculate the dose-equivalent quantities. The conversion
coefficients for the “monoenergetic” neutrons at the stated energy are used in this case.
With endothermic reactions, two neutron groups are produced near the threshold relative to the
incident proton beam. This is the case for the T(p,n) He reaction if it is used to provide neutron energies
of either 0,144 MeV or 0,25 MeV at 0°. To obtain monoenergetic neutrons of these energies, larger
angles of neutron emission should be used with charged particles of correspondingly higher energies.
Alternatively, the Li(p,n) reaction can be used to produce these energies. For the exothermic T(d,n)
reaction, account shall be taken of neutrons produced by the lower energy D(d,n) reaction, arising from
deuterium implantation during irradiation or pre-existing deuterium contamination of the tritium. To
limit the effects of deuterium implantation, the use of the same target for more than one energy with
the T(d,n) reaction is deprecated.
Excited states of the residual nuclei are formed for scandium and lithium for neutrons produced at 0°
with energies above 0,053 MeV and 0,65 MeV, respectively. These higher particle energies should only
be used if the response of the instrument to the resulting additional neutron energy group, as well as
the relative intensity of the secondary group to that of the primary group, are known.
5.3.4 Parasitic and scattered neutron background
Parasitic neutrons are those that are not part of the desired reference spectrum and occur for example
from scattering and from contaminant reactions. Corrections need to be considered:
a) in the measurement of the neutron fluence;
b) in monitoring the neutron production;
c) in evaluating the performance of the instrument under investigation.
To reduce the effect of scattered neutrons, the room used for the measurements shall be as large as
possible (see 4.8).
To reduce the influence of the scattered neutron background on a measurement, a reaction angle of 0°
should be used wherever possible, and the target assembly mass should be as low as possible.
The effect of parasitic neutron-producing reactions in the target, and of neutrons scattered in the target
assembly, on the neutron energy distribution shall be determined.
The background resulting from reactions of the beam in the target backing, or in material used to
absorb the reacting element, e.g. titanium for tritium and deuterium targets, can be accounted for
with "blank target" measurements, where a non-active target, having the same construction details
and materials, is irradiated. Scattering of neutrons in the target assembly is best accounted for using
neutron transport calculations.
Target properties should be monitored by time-of-flight neutron spectrometry to investigate depth
[42]
profiles of reacting isotopes, impurities, and deuterium implantation .
ISO 8529-1:2021(E)
5.3.5 Neutron fluence measurement and monitoring
Practical guidance on the measurement of neutron fluence can be found in Reference [28] and may be
obtained from neutron reference laboratories. Appropriate methods and instruments may include:
a) counters measuring recoil protons (hydrogen-filled proportional counters, recoil-proton
telescopes, scintillation detectors);
b) activation of threshold and resonance detectors;
c) fission fragment detectors;
d) detectors of well-known, calibrated efficiency (for example a precision long counter).
The neutron fluence shall be determined at the location of the instrument to be calibrated. If the
measurements with the reference instrument are done at a different distance to the measurements
with the calibration measurements for the instruments to be calibrated, the distance dependence of the
neutron fluence including air scattering shall be considered. Attention should be paid that the same solid
angle is covered by the reference instrument and the object under test. One or more fluence monitors
[43]
at other positions shall be used during the calibration . The monitors then indicate the fluence at the
location of calibration. Account should be taken of the possible perturbation in the monitor reading
due to the presence of the reference instrument or the device to be calibrated. A correction can be
determined by carrying out two consecutive measurements with and without the object in place.
The duration of these measurements shall be such that the integrated beam current can be used as a
monitor for this period.
5.4 Neutron reference radiation fields produced with reactors
5.4.1 General requirements
For calibration purposes, unidirectional beams of neutrons shall be used. If the diameter of the beam is
small compared to the dimensions of the measuring device under investigation, broad beam irradiation
[44]
may be simulated by appropriate sweeping of the measuring device across the beam .
5.4.2 Production and monitoring
The production of quasi-monoenergetic neutron radiation fields by means of filtered reactor neutron
beams makes use of the existence of deep relative minima in the total cross-sections of certain
materials at distinct energies (for exampl
...