SIST EN ISO 19581:2025

SLOVENSKI STANDARD
01-december-2025
Merjenje radioaktivnosti - Radionuklidi, ki sevajo gama žarke - Metoda hitrega
presejanja z uporabo scintilacijskega zaznavala in gama spektrometrije (ISO
19581:2025)
Measurement of radioactivity - Gamma emitting radionuclides - Rapid screening method
using scintillation detector gamma-ray spectrometry (ISO 19581:2025)
Mesurage de la radioactivité - Radionucléides émetteurs gamma - Méthode d'essai de
dépistage par spectrométrie gamma utilisant des détecteurs par scintillation (ISO
19581:2025)
Ta slovenski standard je istoveten z: EN ISO 19581:2025
ICS:
17.240 Merjenje sevanja Radiation measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 19581
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2025
EUROPÄISCHE NORM
ICS 17.240 Supersedes EN ISO 19581:2020
English Version
Measurement of radioactivity - Gamma emitting
radionuclides - Rapid screening method using scintillation
detector gamma-ray spectrometry (ISO 19581:2025)
Mesurage de la radioactivité - Radionucléides
émetteurs gamma - Méthode d'essai de dépistage par
spectrométrie gamma utilisant des détecteurs par
scintillation (ISO 19581:2025)
This European Standard was approved by CEN on 28 September 2025.

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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19581:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 19581:2025) has been prepared by Technical Committee ISO/TC 85 "Nuclear
energy, nuclear technologies, and radiological protection " in collaboration with 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 April 2026, and conflicting national standards shall be
withdrawn at the latest by April 2026.
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.
This document supersedes EN ISO 19581:2020.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. 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 19581:2025 has been approved by CEN as EN ISO 19581:2025 without any modification.

International
Standard
ISO 19581
Second edition
Measurement of radioactivity —
2025-09
Gamma emitting radionuclides
— Rapid screening method using
scintillation detector gamma-ray
spectrometry
Mesurage de la radioactivité — Radionucléides émetteurs
gamma — Méthode d'essai de dépistage par spectrométrie
gamma utilisant des détecteurs par scintillation
Reference number
ISO 19581:2025(en) © ISO 2025
ISO 19581:2025(en)
© ISO 2025
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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 19581:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions . 2
4 Symbols . 3
5 Principle . 4
6 Apparatus . 6
7 Sample container . 7
8 Procedure . 8
8.1 Packaging of samples for measuring purposes .8
8.2 Calibration .8
8.2.1 General .8
8.2.2 Reference source .9
8.2.3 Check source .9
8.2.4 Energy calibration.9
8.2.5 Detection efficiency calibration .10
8.3 Validation of the screening level . 12
8.4 Screening procedure . 12
8.4.1 Total spectrum counting/Single channel analyser counting. 12
8.4.2 Multichannel analyser counting . 13
8.4.3 Effect of sample density . 13
9 Test report . 14
Annex A (informative) Example of application of this document for radio-caesium screening .16
Bibliography .21

iii
ISO 19581:2025(en)
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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 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, Radiological protection, in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 430, Nuclear energy, nuclear technologies,
and radiological protection, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 19581:2017), which has been technically
revised.
The main changes are as follows:
— the updated IAEA Nuclear Safety and Security Glossary was referenced;
— Annex A has been updated with considering recent technological improvements;
— editorial changes have been made.
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 19581:2025(en)
Introduction
Everyone is exposed to natural radiation. The natural sources of radiation are cosmic rays and naturally
occurring radioactive substances which exist in the earth and within the human body. Human activities
involving the use of radiation and radioactive substances add to the radiation exposure from this natural
exposure. Some of those activities, such as the mining and use of ores containing naturally occurring
radioactive materials (NORM) and the production of energy by burning coal that contains such substances,
simply enhance the exposure from natural radiation sources. Nuclear power plants and other nuclear
installations use radioactive materials and produce radioactive effluent and waste during operation and on
their decommissioning. The use of radioactive materials in industry, agriculture and research is expanding
around the globe.
All these human activities give rise to radiation exposures that are only a small fraction of the global average
level of natural exposure. The medical use of radiation is the largest and a growing human-made source of
radiation exposure in developed countries. It includes diagnostic radiology, radiotherapy, nuclear medicine
and interventional radiology.
Radiation exposure also occurs as a result of occupational activities. It is incurred by workers in industry,
medicine and research using radiation or radioactive substances, as well as by crew during air travel and
for astronauts. The average level of occupational exposures is generally similar to the global average level of
[1]
natural radiation exposure .
As uses of radiation increase, so do the potential health risk and the public's concerns. Thus, all these
exposures are regularly assessed in order to
a) improve the understanding of global levels and temporal trends of public and worker exposure,
b) evaluate the components of exposure so as to provide a measure of their relative importance, and
c) identify emerging issues that may warrant more attention and study.
While doses to workers are mostly directly measured, doses to the public are usually assessed by indirect
methods using radioactivity measurements results performed on various sources: waste, effluent and/or
environmental samples.
To ensure that the data obtained from radioactivity monitoring programmes support their intended use,
it is essential that the stakeholders, for example, nuclear site operators, regulatory and local bodies agree
on appropriate methods and procedures for obtaining representative samples and then handling, storing,
preparing and measuring the test samples. An assessment of the overall measurement uncertainty needs
also to be carried out systematically. As reliable, comparable and ‘fit for purpose’ data are an essential
requirement for any public health decision based on radioactivity measurements, International Standards
of tested and validated radionuclide test methods are an important tool for the production of such
measurement results. The application of standards serves also to guarantee comparability over time of
the test results and between different testing laboratories. Laboratories apply them to demonstrate their
technical qualifications and to successfully complete proficiency tests during interlaboratory comparison,
two prerequisites for obtaining national accreditation. Today, over a hundred International Standards,
prepared by Technical Committees of the International Organization for Standardization (ISO), including
those produced by ISO/TC85, and the International Electrotechnical Commission (IEC), are available for
application by testing laboratories to measure the main radionuclides.
Generic standards help testing laboratories to manage the measurement process by setting out the general
requirements and methods to calibrate and validate techniques. These standards underpin specific
standards which describe the test methods to be performed by staff, for example, for different types of
samples. The specific standards cover test methods for:
40 3 14
— Naturally occurring radionuclides (including K, H, C and those originating from the thorium and
226 228 234 238 210
uranium decay series, in particular Ra, Ra, U, U, Pb) which can be found in materials from
natural sources or can be released from technological processes involving naturally occurring radioactive
materials (e.g. the mining and processing of mineral sands or phosphate fertilizer production and use);

v
ISO 19581:2025(en)
— Human-made radionuclides, such as transuranium elements (americium, plutonium, neptunium, and
3 14 90
curium), H, C, Sr and gamma emitting radionuclides found in waste, liquid and gaseous effluent, in
environmental matrices (water, air, soil, biota) and food and feed as a result of authorized releases into
the environment and of fallout resulting from the explosion in the atmosphere of nuclear devices and
accidents, such as those that occurred in Chernobyl and Fukushima.
Environmental materials, including foodstuffs, thus may contain radionuclides at activity concentrations
which could present a risk to human health. In order to assess the potential human exposure to radioactivity
and to provide guidance on reducing health risks by taking measures to decrease radionuclide activity
concentrations, the environment and foodstuffs are routinely monitored for radioactivity content as
recommended by the World Health Organization (WHO). Gamma-emitting radionuclides are usually
quantified in environmental and food samples by gamma-ray spectrometry using High Purity Germanium
(HPGe) gamma-ray spectrometry. Following a nuclear accident, a screening approach based on rapid
test methods is recommended to help the decision makers to decide whether activity concentrations in
environmental samples, feed and food samples are above or below operational intervention levels (OILs)
[2]
that are specifically set up to determine the appropriate protective actions. During nuclear emergency
response, these default radionuclide specific OILs for food, milk and water concentrations from laboratory
analysis would be used to measure the effectiveness of protective actions and contribute to determining any
[2][3]
further actions required .
In 1989, following the Chernobyl accident, the first version of the Codex Guideline Levels (GLs) for
Radionuclides in Foods Contaminated Following a Nuclear or Radiological Emergency (in the following
referred to as “Codex GLs”) was adopted. The Codex GLs were reviewed in 2006 and are included in the
[4][5]
General Standard for Contaminants and Toxins in Food and Feeds . During a nuclear emergency situation,
106 106 131 −1
the Codex GLs for gamma-emitting radionuclides such as Ru/ Rh and I is 100 Bq·kg ; the GL for
60 103 137 134 144 −1 −1
Co, Ru, Cs and Cs, Ce is higher at 1 000 Bq·kg but a lower limit of 100 Bq·kg still applies for
foods for infants. Default radionuclide specific OILs for food, milk and water concentrations from laboratory
[6]
analysis set up by FAO, IAEA, ILO, OECD/NEA, PAHO, OCHA, WHO were recently revised .
NOTE The Codex GLs are the activity concentration in foods that would result in an effective dose of 1 mSv/year
for members of the Public (infant and adult) in accordance with the most recent recommendations of the International
Commission on Radiological Protection (ICRP) considering that 550 kg of food is consumed per year by an adult and
200 kg of food and milk is consumed per year by an infant, with 10 % of the diet is of imported food, all of which
is contaminated giving an import to production factor of 0,1. For convenience the GL values were rounded, and
radionuclides with ingestion dose coefficients of similar magnitudes grouped and given similar GLs values. However,
separate GLs were derived for infants and adults due to differences in radionuclide absorption, metabolism and
sensitivity to radiation.
Emergency preparedness should include planning for the implementation of optimized test methods that
can provide rapid estimates of activity concentration to be checked against OILs. Thus, an International
Standard on a screening method using gamma-ray spectrometry is justified for use by testing laboratories
carrying out measurements of gamma-emitting radionuclides during an emergency situation. Such
laboratories are intended to obtain a specific accreditation for radionuclide measurement in environmental
and/or food samples.
This document describes, after proper sampling, sample handling and preparation, a screening method to
quantify rapidly the activity concentration of iodine and caesium in environmental, feedstuffs and foodstuffs
samples using scintillation spectrometer during an emergency situation.
This document is one of a set of generic International Standards on measurement of radioactivity.

vi
International Standard ISO 19581:2025(en)
Measurement of radioactivity — Gamma emitting
radionuclides — Rapid screening method using scintillation
detector gamma-ray spectrometry
WARNING — Persons using this document should be familiar with normal testing laboratory practice.
This document does not purport to address all of the safety problems, if any, associated with its use.
It is the responsibility of the user to establish appropriate safety and health practices and to ensure
compliance with any national regulatory conditions.
IMPORTANT — It is absolutely essential that tests conducted according to this document be carried
out by suitably trained staff.
1 Scope
This document specifies a screening test method to quantify rapidly the activity concentration of gamma-
131 132 134 137
emitting radionuclides, such as I, Te, Cs and Cs, in solid or liquid test samples using gamma-
ray spectrometry with lower resolution scintillation detectors as compared with the HPGe detectors (see
[7] .
IEC 61563 )
This test method can be used for the measurement of any potentially contaminated environmental matrices
(including soil), food and feed samples as well as industrial materials or products that have been properly
[8]
conditioned . Sample preparation techniques used in the screening method are not specified in this
document, since special sample preparation techniques other than simple machining (cutting, grinding,
etc.) should not be required. Although the sampling procedure is of utmost importance in the case of the
measurement of radioactivity in samples, it is out of scope of this document; other International Standards
for sampling procedures that can be used in combination with this document are available (see References
[9] [10] [11] [12] [13] [14]).
131 134 137
The test method applies to the measurement of gamma-emitting radionuclides such as I, Cs and Cs.
Using sample sizes of 0,5 l to 1,0 l in a Marinelli beaker and a counting time of 5 min to 20 min, decision
−1
threshold of 10 Bq·kg can be achievable using a commercially available scintillation spectrometer [e.g.
thallium activated sodium iodide (NaI(Tl)) spectrometer 2” ϕ × 2” (50,8 mm Ø x 50,8 mm) detector size, 7 %
resolution (FWHM) at 662 keV, 30 mm lead shield thickness].
This test method also can be performed in a “makeshift” laboratory or even outside a testing laboratory on
samples directly measured in the field where they were collected.
During a nuclear or radiological emergency, this test method enables a rapid measurement of the activity
concentration of potentially contaminated samples to check against operational intervention levels (OILs)
set up by decision makers that would trigger a predetermined emergency response to reduce existing
[2]
radiation risks .
Due to the uncertainty associated with the results obtained with this test method, test samples requiring
more accurate test results can be measured using high purity germanium (HPGe) detectors gamma-ray
[15][16]
spectrometry in a testing laboratory, following appropriate preparation of the test samples .
This document does not contain criteria to establish the activity concentration of OILs.
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 19581:2025(en)
ISO 11929 (all parts), Determination of the characteristic limits (decision threshold, detection limit and limits of
the confidence interval) for measurements of ionizing radiation — Fundamentals and application
ISO 80000-10, Quantities and units — Part 10: Atomic and nuclear physics
IEC 61453, Nuclear instrumentation — Scintillation gamma ray detector systems for the assay of radionuclides
– Calibration and routine tests
3 Terms, definitions
For the purposes of this document, the terms and definitions given in ISO 80000-10 and the following 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
blank sample
sample of a similar material to the test sample but containing radioactive impurities negligible in comparison
with the test sample
[SOURCE: ISO 20042:2019, 3.2]
3.2
emergency
non-routine situation or event that necessitates prompt action, primarily to mitigate a hazard or adverse
consequences for human life and health, property and the environment
[SOURCE: IAEA. IAEA Nuclear Safety and Security Glossary: 2022 edition. Vienna: IAEA, 2022. 248 p.]
Note 1 to entry: This includes nuclear and radiological emergencies and conventional emergencies such as fires,
release of hazardous chemicals, storms or earthquakes. It includes situations for which prompt action is warranted to
[2]
mitigate the effects of a perceived hazard .
3.3
operational intervention level
OIL
set level of a measurable quantity that corresponds to a generic criterion
[SOURCE: IAEA. IAEA Nuclear Safety and Security Glossary: 2022 edition. Vienna: IAEA, 2022. 248 p.]
Note 1 to entry: OILs are typically expressed in terms of dose rates or of activity of radioactive material released, time
integrated air activity concentrations, ground or surface concentrations, or activity concentrations of radionuclides
in environmental, food or water samples. An OIL is used immediately and directly (without further assessment) to
[2]
determine the appropriate protective actions on the basis of an environmental measurement .
3.4
reference level
level of dose, risk or activity concentration
above which it is not appropriate to plan to allow exposures to occur and below which optimization of
protection and safety would continue to be implemented
[SOURCE: IAEA Nuclear Safety and Security Glossary: 2022 edition. Vienna: IAEA, 2022. 248 p.]
Note 1 to entry: The value chosen for a reference level will depend upon the prevailing circumstances for the exposure
under consideration.
ISO 19581:2025(en)
3.5
response
R
ratio of the indicated value of a meter to the conventional true value (reference activity).
Note 1 to entry: In many cases, the net count rate can serve as the indicated value. The response is also applicable to
equipment that provides direct indicated value of activity or activity concentration.
3.6
screening level
SL
values that are set up by the laboratory taking into account the characteristics of the measuring equipment
and the test method to guarantee that the test result and its uncertainty obtained are fit for purpose for
comparison with the operational intervention levels(OILs) (3.3)
Note 1 to entry: The screening level is less than the operational intervention level.
Note 2 to entry: Food is safe for consumption if the screening level is not exceeded.
4 Symbols
For the purposes of this document, the following symbols apply.
A Activity of each radionuclide in reference source, at the measurement time, in becquerels.
c Activity concentration of each radionuclide expressed in becquerels per kilogram.
A
c Activity concentration that corresponds to the screening level of each radionuclide expressed
A,SL
in becquerels per kilogram.
c Activity concentration that corresponds to the reference level of each radionuclide expressed
A,RL
in becquerels per kilogram.
*
Decision threshold, without and with corrections, in becquerels per kilogram.
c
A
#
Detection limit, without and with corrections, in becquerels per kilogram.
c
A

Upper limits of the confidence interval, in becquerels per kilogram.
c
A
R Response of specific radionuclide, i.
i
ε Counting efficiency of the detector at energy, E.
E
ε Radionuclide-specific counting efficiency of the detector at energy, E, of specific radionuclide, i.
i,E
n , Number of net counts in the gamma-ray energy region of interest, at energy E, in the sample
N,E
spectrum, in the calibration spectrum and in the spectrum obtained from the measurement
n ,
Ns,E
of reference sample having activity that corresponds to the screening level, respectively.
n
N,SL,E
n , n , Number of gross counts in the gamma-ray energy region of interest, at energy E, in the sample
g,E gb,E
spectrum, in the background spectrum, in the calibration spectrum and in the spectrum
n , n
gs,E g,SL,E
obtained from the measurement of reference sample having activity that corresponds to
the screening level, respectively.
P Probability of the emission (emission intensity) of a gamma ray with energy, E, of each ra-
E
dionuclide, per decay.
t Sample counting live time, in seconds.
g
ISO 19581:2025(en)
t Background counting live time, in seconds.
b
t Reference source counting live time, in seconds.
s
t Counting live time, in seconds, of a reference sample with an activity corresponding to a
SL
screening level.
t The two sided t-distribution with k − 1 degree of freedom and α two sides probability.
k-1,α
u(c ) Standard uncertainty associated with the measurement result c , without and with correc-
A A
tions, in becquerels per kilogram.
U Expanded uncertainty calculated by U = k∙u(c ) with k = 1, 2., in becquerels per kilogram.
A
m Mass of the sample for test, in kilograms.
α, β Probability of a false positive and false negative decision, respectively.
1 − γ Probability for the coverage interval of the measurand.
5 Principle
During a nuclear or radiological emergency, it is essential to measure rapidly the activity concentration in
samples from the environment and potentially contaminated foodstuffs and feed to protect workers and
[3]
the public, in accordance with International Standards, by keeping doses below the dose reference levels .
It is recognized among organizations responsible for emergency management that good preparedness
can substantially improve the emergency response. Thus default OILs for food are set up by national
authorities, and measurement procedures using commonly available contamination screening equipment
are implemented to meet the OILs criteria. This should be carried out as part of the emergency preparedness
process. The process of assessing radionuclide concentrations in food, milk and water is shown in Figure 1.
During the process of assessing radionuclide concentrations in food, milk and water the potentially
contaminated food should be screened over a wide area and analysed to determine promptly the activity
concentration of gross and/or individual radionuclides. If the OILs are not exceeded, the food, milk and
water are safe for consumption during the emergency phase. If an OIL is exceeded, the radionuclide specific
concentrations in the food, milk or water should be determined. Finally, as soon as possible the guidance
in Reference [21] should be used to determine whether the food, milk or water is suitable for international
[22]
trade, and national criteria or WHO guidance should be used to determine whether the food, milk or
[6]
water is suitable for long term consumption after the emergency phase .

ISO 19581:2025(en)
Figure 1 — Example of process of assessing radionuclide concentrations in food
(see explanations in the text and modified from Reference [6])
Laboratories shall make the necessary arrangements to be able to perform appropriate and reliable analyses
of environmental and food/feed samples for the purposes of an emergency response. Thus, a screening
approach is required, using a fast test method that rapidly provides test results to the decision maker in
order to determine whether food or feed is suitable for either human or animal consumption during the post
nuclear or radiological emergency monitoring period and for international trade.
The main radioactive materials released into the atmosphere during a power plant nuclear accident
131 132 133 134 136 137
are volatile elements including iodine isotopes ( I, I, I), caesium isotopes ( Cs, Cs, Cs) and
tellurium ( Te). Samples taken from the environment, the foodstuffs and feed can initially contain high
131 [23]
activity concentrations of I relative to the caesium isotopes . Although often activity released is also
dominated by noble gases, these cannot end up in food.
Therefore, the monitoring that shall be implemented immediately following a nuclear or radiological
emergency requires a test method designed for the screening of I activity concentration of environmental
and food samples. When using a test method with a scintillation detector system incorporating a
spectrometer (hereinafter referred to as scintillation spectrometer) or a portable gamma-ray detector (e.g.
survey meter) with no radionuclide discrimination function, I is not determined separately from other
iodine isotopes and caesium isotopes due to poor detector energy resolution. When using a test method with
131 134 137
a scintillation spectrometer I, Cs and Cs can be discriminated and potentially quantified. However,
using a multichannel analyser (MCA) with a peak deconvolution programme does not avoid the contributions
in the energy region of interest of other radionuclides, including short-lived iodine isotopes, caesiums and
naturally occurring radionuclides. The I activity concentration may be therefore overestimated but this
is considered as acceptable during the immediate phase following a nuclear or radiological emergency to
rapidly assess the contamination.
A few months after the nuclear or radiological emergency, the short-lived radionuclides, including iodine
134 137
isotopes, have decayed. Longer-lived radionuclides including Cs and Cs become predominant in
environmental and food samples. During this later period, when using a test method with a portable
134 137
gamma-ray detector (e.g. survey meter) with no radionuclide discrimination function, Cs and Cs
activity concentration cannot be quantified separately and the test result is considered as the gross activity
134 137
of both Cs and Cs. With a scintillation spectrometer, individual nuclide activity concentrations can

ISO 19581:2025(en)
be determined. However, contributions from naturally occurring radionuclides might be unavoidable even
during this later period.
134 137
NOTE In the later stage, the radionuclide composition is usually known, including the ratio of Cs to Cs; it
allows to estimate the activity concentration of the individual caesium isotopes using the gross activity results.
Direct measurement without iodine retention treatment, evaporation or ashing can be used to measure the
activity concentration rapidly during the nuclear or radiological emergency and post nuclear or radiological
emergency monitoring period. The test sample is measured directly without any preparation, preferably in
a Marinelli beaker type container.
As the tests are performed to check the activity concentration of the sample against OILs set up by national
authority, screening levels should be set in a range from half of these OILs to close to the OILs in order to
avoid false-positives.

Upper limit of confidence interval of the best estimate of the true value for the screening level, C , shall be
A,SL
below that for the reference level, C , with a 95 % confidence level (α = 0,05, k = 2) as shown in the
A,RL
following Formula (1):

CC=+tu⋅ CC< (1)
()
AA,,SL SL kA−1,,α SL A,RL
where
t is the two sided t-distribution;
uC() is the uncertainty of the best estimate of the true value for the screening level.
A,SL
The probability distribution function associated with the test results can be obtained by repeating the tests
on the same samples. uC should be determined by repeated measurement with the minimum counting
()
A,SL
time of a reference source or reference material with an activity close to the screening level of the

radionuclide tested and containing no other radionuclide. C should specify the number of repeated
A,SL
measurements which would enable the use of a t-distribution (see 8.3). This document recommends to
repeat the measurements of the same sample a minimum of 4 times.
In order to ensure the reliability of the screening test, the decision threshold, see ISO 11929 (series), is
defined taking into consideration that the counting time shall be shortened to obtain the test results rapidly
for a large number of samples. This document recommends that one-fourth of the OIL value is an appropriate
value for the decision threshold.
NOTE False negatives are not considered in this document. In many cases, however, it is expected that the
probability of false negatives occurring at the SL determined by Formula (1) could be equal to the probability of false
positives occurring. The probability of false negatives occurring can also be reduced by setting a lower SL than the SL
determined by Formula (1).
6 Apparatus
Several types of scintillation spectrometers can be used for sample screening. Commercially available
scintillation crystals that would be useful for the screening test are shown in Table 1.

ISO 19581:2025(en)
Table 1 — Examples of commercially available scintillation crystals with typical detector size and
its resolution
Crystal Detector size Resolution at 662 keV
50,8 mm ϕ ×50,8 mm
a
NaI(Tl) <8 %
127 mm ϕ ×127 mm
b
CsI(Tl) 110 mm ϕ ×25 mm 10 %
c
LaBr (Ce) 38,1 mm ϕ ×38,1 mm 3 %
d
SrI(Eu) 25,4 mm ϕ ×25,4 mm <4 %
e,f
CeBr 50,8 mm ϕ ×50,8 mm <4 %
g
GAGG(Ce) 50,8 mm ϕ ×50,8 mm <7 %
h
BGO 50,8 mm ϕ ×50,8 mm 10 %
i
CLYC 50,8 mm ϕ ×50,8 mm <5 %
a
Alpha Spectra, Inc., Large Volume Detectors Data Sheet. https:// alphaspectra .com/ wp -content/ uploads/ ASI -Large -Volume
-Detectors -Data -Sheet .pdf
b
Hamamatsu Photonics K.K., C12137 series. https:// www .hamamatsu .com/ content/ dam/ hamamatsu -photonics/ sites/
documents/ 99 _SALES _LIBRARY/ ssd/ c12137 _series _kacc1196e .pdf
c
Mirion Technologies, Inc. Lanthanum Bromide Scintillation Detector. https:// www .mirion .com/ products/ technologies/
spectroscopy -scientific -analysis/ gamma -spectroscopy/ detectors/ scintillation -czt -detectors -accessories/ labr3 -15 -x -15
-lanthanum -bromide -scintillation -detector
d
RADIATION MONITORING DEVICES, Gamma Scintillator Properties SrI2. https:// www .rmdinc .com/ assets/ Strontium -Iodide
-SrI2 -Gamma -Scintillator -Properties .pdf
e
Scionix Holland B.V., Properties and use of scintillation materials. https:// scionix .nl/ scintillation -crystals/ #tab -id -5
f
Hellma Materials, Radiation Detection Materials. https:// www .hellma .com/ fileadmin/ fos/ Website/ Broschueren _Flyer
_Handhabung/ Hellma _Materials/ Englisch/ Radiation _Detection _Materials .pdf
g
Corporation, Products information of GAGG. https:// www .c -and -a .jp/ products _details/ products _detail _GAGG .html
h
Alpha Spectra, Inc., BGO Detectors Data Sheet. https:// alphaspectra .com/ wp -content/ uploads/ ASI -BGO -Detectors -Data
-Sheet -1 .pdf
i
RADIATION MONITORING DEVICES, Gamma Scintillator Properties CLYC. https:// www .rmdinc .com/ assets/ CLYC -Gamma
-Neutron -Scintillator -Properties .pdf
NOTE These are examples of a suitable product available. This information is given for the convenience of users of this
document and does not constitute an endorsement by ISO of these products.
A spectrometry apparatus consists of two parts: the scintillation detector with plug-on or external
electronics and multi-channel analyser and the device which handles, stores, and analyses the measured
spectra. The instrument is typically connected to a PC for control or analysis when installed and used in a
laboratory. Digital signal processing electronics are commonly used. Portable scintillation spectrometers
(e.g. survey meter) for in situ measurements are also available. For screening, a simple total spectrum
counting system that counts all pulses above a low-energy threshold or single-channel analyser (SCA)
counting system that co
...