EN ISO 18589-3:2017

SLOVENSKI STANDARD
01-december-2017
Merjenje radioaktivnosti v okolju - Tla - 3. del: Preskusna metoda za radionuklide,
ki sevajo žarke gama, s spektrometrijo gama (ISO 18589-3:2015, popravljena
različica 2015-12-01)
Measurement of radioactivity in the environment - Soil - Part 3: Test method of gamma-
emitting radionuclides using gamma-ray spectrometry (ISO 18589-3:2015, Corrected
version 2015-12-01)
Ermittlung der Radioaktivität in der Umwelt - Erdboden - Teil 3: Messung von
Gammastrahlen emittierenden Radionukliden mittels Gammaspektrometrie (ISO 18589-
3:2015, korrigierte Fassung 2015-12-01)
Mesurage de la radioactivité dans l'environnement - Sol - Partie 3: Méthode d'essai des
radionucléides émetteurs gamma par spectrométrie gamma (ISO 18589-3:2015, Version
corrigée 2015-12-01)
Ta slovenski standard je istoveten z: EN ISO 18589-3:2017
ICS:
13.080.99 Drugi standardi v zvezi s Other standards related to
kakovostjo tal soil quality
17.240 Merjenje sevanja Radiation measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 18589-3
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2017
EUROPÄISCHE NORM
ICS 17.240; 13.080.01
English Version
Measurement of radioactivity in the environment - Soil -
Part 3: Test method of gamma-emitting radionuclides
using gamma-ray spectrometry (ISO 18589-3:2015,
Corrected version 2015-12-01)
Mesurage de la radioactivité dans l'environnement - Ermittlung der Radioaktivität in der Umwelt -
Sol - Partie 3: Méthode d'essai des radionucléides Erdboden - Teil 3: Messung von Gammastrahlen
émetteurs gamma par spectrométrie gamma (ISO emittierenden Radionukliden mittels
18589-3:2015, Version corrigée 2015-12-01) Gammaspektrometrie (ISO 18589-3:2015, korrigierte
Fassung 2015-12-01)
This European Standard was approved by CEN on 13 September 2017.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 18589-3:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 18589-3:2015, Corrected version 2015-12-01 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 18589-3:2017
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 April 2018, and conflicting national standards shall be
withdrawn at the latest by April 2018.
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.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 18589-3:2015, Corrected version 2015-12-01 has been approved by CEN as EN ISO
18589-3:2017 without any modification.

INTERNATIONAL ISO
STANDARD 18589-3
Second edition
2015-02-15
Corrected version
2015-12-01
Measurement of radioactivity in the
environment — Soil —
Part 3:
Test method of gamma-emitting
radionuclides using gamma-ray
spectrometry
Mesurage de la radioactivité dans l’environnement — Sol —
Partie 3: Méthode d’essai des radionucléides émetteurs gamma par
spectrométrie gamma
Reference number
ISO 18589-3:2015(E)
©
ISO 2015
ISO 18589-3:2015(E)
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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the requester.
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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2015 – All rights reserved

ISO 18589-3:2015(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 2
3.1 Terms and definitions . 2
3.2 Symbols . 2
4 Principle . 2
5 Gamma-spectrometry equipment . 3
6 Sample container . 4
7 Procedure. 4
7.1 Packaging of samples for measuring purposes . 4
7.2 Laboratory background level . 5
7.3 Calibration . 5
7.3.1 Energy calibration . 5
7.3.2 Efficiency calibration. 5
7.4 Measurements of and corrections for natural radionuclides . 6
8 Expression of results . 6
8.1 Calculation of the activity per unit of mass . 6
8.1.1 General. 6
8.1.2 Decay corrections . 7
8.1.3 Self-absorption correction . 7
8.1.4 Summation effects or coincidence losses corrections . 8
8.2 Standard uncertainty . 8
8.3 Decision threshold . 9
8.4 Detection limit . 9
8.5 Confidence limits.10
8.6 Corrections for contributions from other radionuclides and background .10
8.6.1 General.10
8.6.2 Contribution from other radionuclides .10
8.6.3 Contribution from background .12
9 Test report .12
Annex A (informative) Calculation of the activity per unit mass from a gamma spectrum
using a linear background subtraction .14
Annex B (informative) Analysis of natural radionuclides in soil samples using
gamma spectrometry .16
Bibliography .22
ISO 18589-3:2015(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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 2, Radiological protection.
This second edition cancels and replaces the first edition (ISO 18589-3:2007), which has been
technically revised.
ISO 18589 consists of the following parts, under the general title Measurement of radioactivity in the
environment — Soil:
— Part 1: General guidelines and definitions
— Part 2: Guidance for the selection of the sampling strategy, sampling and pre-treatment of samples
— Part 3: Test method of gamma-emitting radionuclides using gamma-ray spectrometry
— Part 4: Measurement of plutonium isotopes (plutonium 238 and plutonium 239 + 240) by alpha spectrometry
— Part 5: Measurement of strontium 90
— Part 6: Measurement of gross alpha and gross beta activities
— Part 7: In situ measurement of gamma-emitting radionuclides
This corrected version of ISO 18589-3:2015 incorporates a correction to Formula (4).
iv © ISO 2015 – All rights reserved

ISO 18589-3:2015(E)
Introduction
This part of ISO 18589 is published in several parts to be used jointly or separately according to needs.
ISO 18589-1 to ISO 18589-6, concerning the measurements of radioactivity in the soil, have been
prepared simultaneously. These parts are complementary and are addressed to those responsible for
determining the radioactivity present in soils. The first two parts are general in nature. ISO 18589-3
to ISO 18589-5 deal with radionuclide-specific measurements and ISO 18589-6 with non-specific
measurements of gross alpha or gross beta activities. ISO 18589-7 deals with the measurement of
gamma-emitting radionuclides using in situ spectrometry.
Additional parts can be added to ISO 18589 in the future if the standardization of the measurement of
other radionuclides becomes necessary.
INTERNATIONAL STANDARD ISO 18589-3:2015(E)
Measurement of radioactivity in the environment — Soil —
Part 3:
Test method of gamma-emitting radionuclides using
gamma-ray spectrometry
1 Scope
This part of ISO 18589 specifies the identification and the measurement of the activity in soils of a large
number of gamma-emitting radionuclides using gamma spectrometry. This non-destructive method,
applicable to large-volume samples (up to about 3 000 cm ), covers the determination in a single
measurement of all the γ-emitters present for which the photon energy is between 5 keV and 3 MeV.
This part of ISO 18589 can be applied by test laboratories performing routine radioactivity
measurements as a majority of gamma-emitting radionuclides is characterized by gamma-ray emission
between 40 keV and 2 MeV.
The method can be implemented using a germanium or other type of detector with a resolution
better than 5 keV.
This part of ISO 18589 is addressed to people responsible for determining gamma-emitting radionuclides
activity present in soils for the purpose of radiation protection. It is suitable for the surveillance of the
environment and the inspection of a site and allows, in case of accidents, a quick evaluation of gamma
activity of soil samples. This might concern soils from gardens, farmland, urban or industrial sites that
can contain building materials rubble, as well as soil not affected by human activities.
When the radioactivity characterization of the unsieved material above 200 μm or 250 μm, made of
petrographic nature or of anthropogenic origin such as building materials rubble, is required, this
material can be crushed in order to obtain a homogeneous sample for testing as described in ISO 18589-2.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 10703, Water quality — Determination of the activity concentration of radionuclides — Method by
high resolution gamma-ray spectrometry
ISO 11074, Soil quality — Vocabulary
ISO 11929, Determination of the characteristic limits (decision threshold, detection limit and limits of the
confidence interval) for measurements of ionizing radiation — Fundamentals and application
ISO 18589-1, Measurement of radioactivity in the environment — Soil — Part 1: General guidelines
and definitions
ISO 18589-2, Measurement of radioactivity in the environment — Soil — Part 2: Guidance for the selection
of the sampling strategy, sampling and pre-treatment of samples
ISO 80000-10, Quantities and units — Part 10: Atomic and nuclear physics
IEC 61452, Nuclear instrumentation — Measurement of gamma-ray emission rates of radionuclides —
Calibration and use of germanium spectrometer
ISO 18589-3:2015(E)
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 10703, ISO 11074, ISO 18589-1
and ISO 80000-10 apply.
3.2 Symbols
m mass of the test portion, in kilograms
A activity of each radionuclide in the calibration source, at the calibration time, in becquerel
a, a activity, in becquerel per kilogram, per unit of mass of each radionuclide, without and with
c
corrections
t sample spectrum counting time, in seconds
g
t ambient background spectrum counting time, in seconds
t calibration spectrum counting time, in seconds
s
n , n , n number of counts in the net area of the peak, at energy, E, in the sample spectrum, in the
N,E N0,E Ns,E
background spectrum and in the calibration spectrum, respectively
n , n , n number of counts in the gross area of the peak, at energy, E, in the sample spectrum, in the
g,E g0,E gs,E
background spectrum and in the calibration spectrum, respectively
n , n , n number of counts in the background of the peak, at energy, E, in the sample spectrum, in
b,E b0,E bs,E
the background spectrum and in the calibration spectrum, respectively
ε efficiency of the detector at energy, E, with the actual measurement geometry
E
P probability of the emission of gamma radiation with energy, E, for each radionuclide, per
E
decay
μ(E), μ (E) linear attenuation coefficient at photon energy, E, of the sample and calibration source,
1 2
respectively, per centimetre
μ (E) mass attenuation coefficient, in square centimetres per gram, at photon energy, E, of ele-
m,i
ment i
h height of the sample in the container, in centimetres
w mass fraction of element i (no unit)
i
ρ bulk density, in grams per cubic centimetre, of the sample
λ decay constant of each radionuclide, per second
u(a), u(a ) standard uncertainty, in becquerel per kilogram, associated with the measurement result,
c
with and without corrections, respectively
.
U expanded uncertainty, in becquerel per kilogram, calculated by U = k u (a) with k = 1, 2, …
decision threshold, in becquerel per kilogram, for each radionuclide, without and with
**
aa,
c
corrections, respectively
detection limit, in becquerel per kilogram, for each radionuclide, without and with correc-
##
aa,
c tions, respectively
lower and upper limits of the confidence interval, for each radionuclide, in becquerel per

aa,
kilogram
4 Principle
The activity of gamma-emitting radionuclides present in the soil samples is determined using gamma
spectrometry techniques based on the analysis of the energies and the peak areas of the full-energy
2 © ISO 2015 – All rights reserved

ISO 18589-3:2015(E)
peaks of the gamma lines. These techniques allow the identification and the quantification of the
[1][2]
radionuclides.
The nature and geometry of the detectors as well as the samples call for appropriate energy and
[1][2]
efficiency calibrations. Both coincidence and random summation effects need to be considered,
particularly with container sitting directly on the detector and Marinelli type container, high activity
levels or with well-type detectors used to measure small-mass samples (see 8.1.4).
NOTE ISO 18589 deals exclusively with gamma spectrometry using semiconductor detectors.
5 Gamma-spectrometry equipment
Gamma-spectrometry equipment generally consists of
— a semiconductor detector with a cooling system (liquid nitrogen, cryogenic assembly, etc.),
— a shield, consisting of lead and/or other materials, against ambient radiation,
— appropriate electronics (high-voltage power supply; signal-amplification system; an analogue-to-
digital converter),
— a multi-channel amplitude analyser, and
— a computer to display the measurement spectra and to process the data.
The semiconductor detectors generally used are made of high-purity germanium crystals (HP Ge). The
type and geometry of these detectors determine their field of application. For example, when detecting
photons with an energy below 400 keV, the use of detectors with a thin crystal is recommended in
order to limit interference from high-energy photons. However, it is better to use a large-volume, P-type
coaxial detector to measure high-energy photons (above 200 keV) or an N-type coaxial detector to
detect both low- and high-energy radiation.
At the level of natural radioactivity, it is advantageous for the measurement to use an ultra-low-level
measuring instrument, i.e. a set-up arranged with a choice of materials for the detector and shielding
that guarantees a very low background level. This includes very low-noise electronic preamplifiers and
amplifiers. The shielding case should be large enough to allow sufficient distance from all walls and the
detector set up in the centre of the case, when 1-l samples are inserted. This allows the use of a room
with a very low specific activity of building materials and a very low radon concentration in the room
air to be chosen. It is optimal to erect the measuring instruments in the middle of the room with the
maximum distance available to the room walls. Forced ventilation of the measuring room can possibly
contribute to stabilizing the background level. On the other hand, forced ventilation can then cause
problems when the outside air drawn in contains excess radon as a result of a warming-up of the soil
(in particular, when the soil thaws in spring). It is always good practice to fill the inner part of the
shielding with nitrogen. For this, the gaseous nitrogen escaping from the Dewar vessel of the detector
arrangement can be passed permanently into the shielding.
The main characteristics that allow the estimation of a detector performance are as follows:
a) energy resolution (total width at half maximum of the full-energy peak), which enables the detector
to separate two neighbouring gamma peaks;
b) absolute efficiency, which specifies the percentage of photons detected in the full-energy peak
relative to the number of photons emitted;
c) peak-to-Compton ratio.
Depending on the required accuracy and the desired detection limit, it is generally necessary to use
high-quality detectors whose energy resolution is less than 2,2 keV (for the Co peak at 1 332 keV) and
with a peak/Compton ratio between 50 and 80 for Cs (see IEC 61452).
ISO 18589-3:2015(E)
210 238 234
Some natural radionuclides, e.g. Pb and U through Th, can be measured only through gamma
lines in the energy range of 100 keV. In this case, the use of an N-type detector is recommended. Low-
energy, low-level detectors offered by manufacturers have been optimized for this purpose and can
additionally be used in other areas of environmental monitoring, e. g. for measurements of I and
Am in samples from the vicinity of nuclear facilities.
[5][6]
The computer, in combination with the available hardware and software, shall be carefully selected.
It is recommended that the results of the computer analysis of the spectrum be visually checked regularly.
Comparison with a certified reference material is recommended to check the performance of the
apparatus. Participation in proficiency and inter-laboratory tests and inter-comparison exercises can
[9][10]
also help to verify the performance of the apparatus and the status of the analysis.
6 Sample container
Measuring gamma radioactivity in soils requires sample containers that are suited to gamma
spectrometry with the following recommended characteristics:
— be made of materials with low absorption of gamma radiation;
— be made of transparent material to see the level of content;
— have volumes adapted to the shape of the detector for maximum efficiency;
— be watertight and not react with the sample constituents;
— have a wide-necked, airtight opening to facilitate filling;
— be unbreakable.
In order to verify easily that the content of the container conforms to the standard counting geometry,
a transparent container with a mark to check the filling can be selected.
7 Procedure
7.1 Packaging of samples for measuring purposes
The soil samples packaged for gamma spectrometry measurements are usually dried, crushed, and
homogenized in accordance with ISO 18589-2.
The procedure shall be carried out as follows.
a) Choose the container that is best suited to the volume of the sample so as to measure as much material
as possible. To decrease self-absorption effects, the height of the contents should be minimized.
b) Fill the container to the level of the volume mark. It is recommended to use a mechanical filling
device (for example, a vibrating table) to pack the sample to avoid any future losses in volume.
c) Note the sample mass. This information is useful when using the measurements to express the
result as specific activity and when carrying out self-absorption corrections.
d) Visually check the upper level of the sample and make sure that it is horizontal before measuring.
Where applicable, add more material to the sample until the mark has been reached and adjust the
noted sample mass accordingly.
e) Hermetically seal the container if volatile or natural radionuclides are being measured.
f) Clean the outside of the container to remove potential contamination due to the filling process.
4 © ISO 2015 – All rights reserved

ISO 18589-3:2015(E)
If measurements are required quickly, the processing method described in ISO 18589-2 can be ignored.
This shall be mentioned in the test report and the results cannot be expressed in becquerels per
kilogram of dry soil.
When measuring Ra-226 through the short-lived decay products of Rn-222, the sealed container shall be
stored long enough (30 d) to allow radioactive equilibrium to be reached between Ra-226 and Rn-222.
7.2 Laboratory background level
As some radionuclides found in the soil (see Annex B) are the same as in building materials, the
detector and sample shall be adequately shielded against natural background radiation. Frequently, it
is sufficient to shield the detector in a 10 cm thick, low-background lead case wall. Reduction of radon
inside the shield is desirable. Further information is given in References [1]and [2].
The natural radionuclides and their decay products occur widely and with large concentration ranges
in floors, walls, ceilings, the air of the measuring rooms and in the materials of which detectors and
shielding are made.
There are isotopes of the decay chain of the rare gas radon, whose emanation from the materials
surrounding the measuring instruments depends on various physical parameters. Thus, large
fluctuations in the concentration of radon and of the decay products can occur in room air and in the air
of the detector shielding. This is a particular problem in basements of old buildings with defective floors.
The background of the measuring instruments shall be kept as low as possible and, in particular, as
stable as possible by appropriate measures. This includes vacuuming the shielding and removing
the dust by filtration. Frequent measurements of the background level permit the verification of its
stability. This is necessary because the peaks of the background spectrum shall be subtracted from
those of a sample spectrum.
7.3 Calibration
7.3.1 Energy calibration
Energy calibration is carried out using sources of a radionuclide with different emission lines (for
example Eu) or sources containing a mixture of several radionuclides. This calibration allows the
establishment of the relationship between the channel numbers of the analyser and the known energy of
[12][13]
the photons. Generally, this task is carried out with appropriate software, which uses the standard
spectra to automatically convert the channel scale of the multi-channel analyzer into a photon energy
scale and to record the useful information necessary for future analyses. By using the energy calibration
spectra, the full width at half the maximum of the full-energy peaks can be determined as a function of
the gamma energy. This information is usually required by the spectrometry analysis software.
Further information is given in IEC 61452, ISO 10703, and References [7] and [8].
7.3.2 Efficiency calibration
Efficiency calibration is carried out either through ab initio calculations of the detector efficiency using
transport theory and Monte Carlo techniques (not covered in ISO 18589) or by using a radionuclide
source having different emission lines or a mixed-radionuclide source. This calibration allows the
establishment of the detection efficiency of the detector as a function of the energy of the radiation.
When using a radionuclide source with different emission lines for calibration, summation effects or
coincidence losses should be taken into account.
The sample measurement shall be performed with the same measuring conditions as used for
calibrating the gamma spectrometry system. In particular, the settings of the electronics (gain and
high voltage), the measurement geometry, the position of the source in relation to the detector and the
sample and standard matrices shall be identical.
ISO 18589-3:2015(E)
For this purpose, a calibration source should have the same physical and chemical properties as the
sample. It might, for instance, be produced by spiking an appropriate sample of soil.
With these conditions, the efficiency at energy E shall be calculated as given in Formula (1):
nt/
Ns,sE
ε = (1)
E
AP⋅
E
For a single peak at an energy E, the count, n , in the net-peak area of a γ-spectrum is calculated as
Ns,E
given in Formula (2):
nn=−n (2)
Ns,,EEgs bs,E
When the physical and chemical nature of the sample (chemical composition, bulk density) is different
from the conditions of the efficiency calibration, a correction for the self-absorption of gamma radiation
should be applied.
Further information is given in IEC 61452, ISO 10703, and References [7] and [8].
7.4 Measurements of and corrections for natural radionuclides
If activities of natural radionuclides in the soil are being measured, the areas of full-energy peaks
used for evaluating their activities shall be corrected for the background contribution of those same
radionuclides inside the detector shielding, taking into account potential differences of the duration of
the sample and background measurements.
Special advice to take into account during the measurement of natural radionuclides in soil and
information on spectroscopic interferences is given in Annex B.
The gamma ray of the radionuclides in the background and/or of natural radionuclides inside the sample
can also interfere with measurements of artificial radionuclides and can require appropriate corrections.
8 Expression of results
8.1 Calculation of the activity per unit of mass
8.1.1 General
The activity per unit of mass, a of each radionuclide present in the sample is obtained from the net
count, n , from the peak of an individual γ-line without interference using Formula (3):
N,E
nt/
Ng,E
a= (3)
Pm⋅⋅ε ⋅ f
EE E
where
f is the correction factor considering all necessary corrections according to Formula (4).
E
ff=⋅ ff⋅⋅ f (4)
EEdatt,,cl EEs,
where
f is the factor to correct for decay for a reference date;
d
f is the factor to correct for self-absorption;
att,E
6 © ISO 2015 – All rights reserved

ISO 18589-3:2015(E)
f is the factor to correct for coincidence losses;
cl,E
f is the factor to correct summing-up effects by coincidences.
s,E
For an undisturbed peak with energy, E, the count, n , in the net-peak area of a γ-spectrum is
N,E
calculated by Formula (5):
nn=−n (5)
Ng,,EE b,E
Thus, Formula (3) can be expressed as given in Formula (6):
nt/ nn−
Ng,,E gbEE,
a= = =−()nn ⋅wt/ withw = (6)
gb,,EE gg
Pm⋅⋅εε⋅f Pm⋅⋅ ⋅⋅ft Pm⋅⋅ε ⋅f
EE E EE E g EE E
if the net-peak area, n , is obtained by unfolding of a multiplet Formula (6) is valid; but, special care is
N,E
needed in calculating the uncertainties according to 8.2.
If a peak is disturbed by an interfering γ-line of another radionuclide and cannot be resolved by
unfolding methods due to the limited resolution of the detector, and if the contribution of the interfering
radionuclide can be estimated from another γ-line of the interfering radionuclide, the procedure
described in 8.6 should be applied.
For nuclides characterized by more than one line, the activity can be computed using several peaks taking
into account the known branching ratios described by their decay scheme and the efficiency curve.
8.1.2 Decay corrections
Depending on the half-life of the radionuclide being measured, the activity per unit of mass shall be
corrected by f . To take into account the radioactive decay during the counting time and during the
d
time between the reference instant (t = 0) and the measuring instant (t = t ), f shall be calculated
i d
by Formula (7):
 λ⋅t 
g
−1 λ⋅t
i
fe=⋅ (7)
 
d
−⋅λ t
g
 
1−e 
8.1.3 Self-absorption correction
Measurement of radioactivity in soils by gamma spectrometry can involve sample whose matrix is
different from that of the calibrated source. In this case, a correction factor should be applied to the
result obtained. The lower the radiation energy, the larger the correction factor.
Different techniques can be used to determine this correction factor:
— measurement of the attenuation coefficient of gamma radiation in the sample material at a given
energy;
— mathematical calculation that takes into account the chemical composition and bulk density of the
sample.
For cylindrical sample containers at the level of the detector, the value of the attenuation correction
factor, f , can be estimated using Formula (8):
att,E
−μ ()EX⋅
μ ()Ee⋅−1
2 ()
f = (8)
att,E
−μ EX⋅
()
μ ()Ee⋅−1
1 ()
where
X is the average test sample thickness in the container, expressed in centimetres.
ISO 18589-3:2015(E)
The linear attenuation coefficient, μ(E), depends on the photon energy, bulk density, chemical
composition of the sample and expresses the exponential decrease of the flux density of gamma rays
with distance. It can be calculated using Formula (9):
 
μμ()Ew= ()E ρ (9)
∑ iim,
 
i
 
As an approximation and for soils of the same nature, the linear attenuation coefficient, μ(E), can be
obtained directly by multiplying the mass attenuation coefficient by the density.
8.1.4 Summation effects or coincidence losses corrections
For radionuclides with cascade transitions, counting losses due to coincidence summing are to be
expected, especially at high counting efficiencies.
These corrections are important for point as well as thin source samples measured very close to the
detector surface; they are specific for each radionuclide, detector, measuring geometry and sample-to-
detector distance.
Most of the theoretical methods for such calculations are related to the use of transport theory and
Monte-Carlo techniques (Geant, EGSnrc, MCNP, Penelope, etc.; see References [13] to [16]); given the
difficulties associated with modelling detectors, some experimental procedures can be applied for each
specific situation.
Some of these experimental procedures use data from specialized literature, but given the wide
range of detector possibilities and measuring conditions, direct measurement as given in a) to c)
below can be made.
a) Prepare a source containing the multi-line photon-emitting radionuclide whose correction factor at
energy, E, shall be calculated along with another radionuclide emitting at a similar energy, E′, which
is mono-energetic or has negligible summing corrections. The geometry shall be the same as that
used for the sample source.
b) Make a measurement with this source at a large distance from the detector. Calculate the
relationship between the net peak counts at energies E and E′.
c) Make a measurement with the sample in the normal measuring position. The relationship between
the net peak counts at energies E and E′ is similar to that calculated above and the theoretical net
T
peak counts, n , at energy E can be estimated.
N,E
T
The relationship between the theoretical net peak counts, n , and the measured net peak counts,
N,E
n , is the summing correction factor for energy E of the multi-line photon emitting radionuclide that
N,E
shall be applied to the analysis of the calibration and source sample spectrum.
Further information is given in References [2] and [8].
8.2 Standard uncertainty
[18]
According to ISO/IEC Guide 98-1:2009, the standard uncertainty of a is calculated by Formula (10):
22 22
 
ua()= wt/(⋅ un +un +⋅au w) (10)
()
() ()
gg,,EEbrel
 
where the uncertainty of the counting time is neglected.
8 © ISO 2015 – All rights reserved

ISO 18589-3:2015(E)
The relative standard uncertainty of w is calculated by Formula (11):
22 22 2
uw()=+uP() um()++uu()ε ()f (11)
relrel EErelrel rel E
Taking Formula (1) into account, the relative standard uncertainty of ε is calculated by Formula (12):
E
22 22 2 22
uu()ε =+()nu ()Au+=()Pu+−(nn )(++uA)(uP ) (12)
relrEEel Ns,,relrel EErelgssb ,,EErelrel
where u (A) includes all the uncertainties related to the calibration source: standard certificate,
rel
preparation of the calibration source.

For the calculation of the characteristic limits (see ISO 11929), it is necessary to know ua(), i.e. the
standard uncertainty of a as a function of its true value. For a true value a , from na=⋅ tw/ +n
gg,,EEb
and with un()=n , one obtains Formula (13):
gg
22 2
 
  
ua()= wt//⋅ tw ⋅+an +un() +⋅au ()w (13)
() ()
gg bb,,EE rel
 
The uncertainties u(n ), u(n ), and u(n ) shall be calculated in accordance with ISO/IEC Guide 98-
N g b
[18]
1:2009, taking into account that the individual counts, n , in channel i of a multi-channel spectrum
i
are the result of a Poisson process and hence u (n ) = n holds. The values of n , n , and n and their
i i N g b
associated standard uncertainties u(n ), u(n ), and u(n ) can be calculated with a computer program.
N g b
Since there are various methods of subtracting the background below a peak in order to derive the
number of counts in the net peak area, no generally applicable formula can be given. An example of the
simple case of linear background subtraction is given in Annex A.
If the net-peak area n , is obtained by a software using unfolding techniques, the software should
N,E
yield n and its associated standard uncertainty. When it provides both n with its associated
b,E
N,E
standard uncertainty, the uncertainties can be calculated according to Formulae (10) to (13). If the code
gives directly a decision threshold and a detection limit for the activity a, these characteristic limits
should be calculated according to ISO 11929, Annex C, in particular C.5. This procedure of ISO 11929
based on Reference [17] is not intended for users but rather for code developers.
8.3 Decision threshold
*

The decision threshold, a , is obtained from Formula (13) for a= 0 (see ISO 11929). This yields
Formula (14):
* 2
ak= ⋅⋅uk 0 = wt/ nu+ n (14)
()
() ()
11−−αα gb,,EEb
α = 0,05 and k α = 1,65 are often chosen by default.
1-
8.4 Detec
...