ISO 4723:2023

INTERNATIONAL ISO
STANDARD 4723
First edition
2023-11
Water quality — Actinium-227 — Test
method using alpha-spectrometry
Qualité de l'eau — Actinium-227 — Méthode d'essai par
spectrométrie alpha
Reference number
© ISO 2023
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ii
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 . 4
5 Sampling, handling and storage . 5
6 Reagents and apparatus . 5
6.1 Reagents . 5
6.2 Apparatus . 6
7 Procedure .7
7.1 Sample preparation . 7
7.2 Coprecipitation . 7
7.3 Purification . 8
7.4 Thin layer source preparation . 8
7.5 Measurement . 8
8 Quality assurance and quality control program . 8
8.1 General . 8
8.2 Variables that can influence the measurement . 8
8.3 Instrument verification . 8
8.4 Contamination . 9
8.5 Interference control . 9
8.6 Method verification . 9
8.7 Demonstration of analyst capability . 9
9 Expression of results . 9
9.1 General . 9
9.2 Tracer activity added . 9
9.3 Count rate and net count rate . 10
9.4 Total recovery . 10
9.5 Activity concentration of Ac in the sample . 10
9.5.1 Direct measurement of Ac . 10
227 215
9.5.2 Indirect measurement of Ac via Po peak after an ingrowth period . 11
9.6 Combined uncertainties . 13
9.7 Decision threshold . 13
9.8 Detection limit . 14
9.9 Probabilistically symmetric coverage interval . 14
9.9.1 Limits of the probabilistically symmetric coverage interval . 14
9.9.2 The shortest coverage interval . 15
10 Test report .15
Annex A (informative) Potential radioactive interferences and examples of alpha spectrum .17
Annex B (normative) Preparation of alpha source by electrodeposition .20
Annex C (normative) Preparation of alpha source by lanthanide fluoride micro-
precipitation .23
Bibliography .25
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 3,
Radioactivity measurements.
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iv
Introduction
Radionuclides are present throughout the environment; thus, water bodies (e.g. surface waters, ground
waters, sea waters) contain radionuclides which can be of either natural, or anthropogenic origin:
3 14 40
— naturally-occurring radionuclides, including, H, C, K and those originating from the thorium
210 210 222 226 228 227 232 231 234
and uranium decay series, in particular Pb, Po, Rn, Ra, Ra, Ac, Th, Pa, U
and U, can be found in water bodies due to either natural processes (e.g. desorption from the soil
and runoff by rain water) or released from technological processes involving naturally-occurring
radioactive materials (e.g. mining, mineral processing, oil, gas, and coal production, water treatment
and the production and use of phosphate fertilisers);
55 59 63 90 99
— anthropogenic radionuclides such as Fe, Ni, Ni, Sr, Tc, transuranic elements (Np, Pu, Am,
60 137
and Cm) and some gamma emitting radionuclides such as Co and Cs can also be found in natural
waters. Small quantities of anthropogenic radionuclides can be discharged from nuclear facilities
to the environment as a result of authorized routine releases. The radionuclides present in liquid
[1]
effluents are usually controlled before being discharged to the environment and water bodies.
Anthropogenic radionuclides used for medical and industrial applications can be released to the
environment after use. Anthropogenic radionuclides are also found in waters due to contamination
from fallout resulting from above-ground nuclear detonations and accidents such as those that have
occurred at the Chornobyl and Fukushima nuclear facilities.
Radionuclide activity concentrations in water bodies can vary according to local geological
characteristics and climatic conditions and can be locally and temporally enhanced by releases from
[2][3]
nuclear installations during planned, existing, and emergency exposure situations . Some drinking-
water sources can thus contain radionuclides at activity concentrations that could present a human
health risk. The World Health Organization (WHO) recommends to routinely monitor radioactivity in
[4]
drinking waters and to take proper actions when needed to minimize the health risk.
National regulations usually specify the activity concentration limits that are authorized in drinking
waters, water bodies, and liquid effluents to be discharged to the environment. These limits can vary
for planned, existing, and emergency exposure situations. As an example, during either a planned or
227 −1
existing situation, the WHO guidance level for Ac in drinking water is 0,1 Bq·l , see Notes 1 and
2. Compliance with these limits is assessed by measuring radioactivity in water samples and by
comparing the results obtained with their associated uncertainties as specified by ISO/IEC Guide 98-3
[5]
and ISO 5667-20 .
NOTE 1 If the value is not specified in Annex 6 of Reference [4], the value has been calculated using the formula
provided in Reference [4] and the dose coefficient data from References [6] and [7].
−1
NOTE 2 The guidance level calculated in Reference [4] is the activity concentration with an intake of 2 l∙d
−1
of drinking water for one year, results in an effective dose of 0,1 mSv∙a to members of the public. This is an
effective dose that represents a very low level of risk to human health and which is not expected to give rise to
[4]
any detectable adverse health effects .
This document contains method(s) to support laboratories, which need to determine Ac in water
samples. The method(s) described in this document can be used for various types of waters (see Scope).
Minor modifications such as sample volume and counting time can be made if needed to ensure that the
characteristic limit, decision threshold, detection limit and uncertainties are below the required limits.
This can be done for several reasons such as emergency situations, lower national guidance limits, and
operational requirements.
v
INTERNATIONAL STANDARD ISO 4723:2023(E)
Water quality — Actinium-227 — Test method using alpha-
spectrometry
WARNING — Persons using this document should be familiar with normal laboratory practices.
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
determine the applicability of any other restrictions.
IMPORTANT — It is essential that tests conducted according to this document be carried out by
suitably trained staff.
1 Scope
This document specifies a test method to determine the activity concentration of Ac in all types of
waters by alpha spectrometry.
The test method is applicable to test samples of supply/drinking water, rainwater, surface and ground
water, marine water, as well as cooling water, industrial water, domestic, and industrial wastewater
after proper sampling and handling and test sample preparation (see ISO 5667-1, ISO 5667-3,
ISO 5667-10). Filtration of the test sample is necessary.
The detection limit depends on the sample volume, the instrument used, the background count rate,
the detection efficiency, the counting time, the chemical yield, and the progeny ingrowth. The method
described in this document, using currently available alpha spectrometry apparatus, has a detection
−1 227
limit of approximately 0,03 Bq·l , when directly measuring the alpha peak of Ac. This detection limit
is lower than the WHO criteria for safe consumption of drinking water for any actinide alpha emitter
−1 [4]
(0,1 Bq·l ). This value can be achieved with a counting time of 48 h for a sample volume of 1 l.
Only a small fraction of Ac decays through alpha emissions (~1,42 %). An option to lower the detection
limit of the method is to wait, let the progenies of Ac grow in, and measure an alpha progeny peak of
227 215 −1
Ac (e.g. Po). This is a longer technique, but a lower detection limit of approximately 0,000 2 Bq·l
can be obtained by re-counting the sample approximately 90 days after purification. The sample can be
re-counted before 90 days, but with a higher detection limit.
The test method(s) described in this document can be used during planned, existing and emergency
exposure situations as well as for wastewaters and liquid effluents with specific modifications that
can increase the overall uncertainty, detection limit and threshold. For an emergency situation, it is
preferable to reduce the counting time rather than the sample volume.
The analysis of Ac adsorbed to suspended matter is not covered by this document.
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/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and
sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 5667-10, Water quality — Sampling — Part 10: Guidance on sampling of waste water
ISO 11929 (all parts), Determination of the characteristic limits (decision threshold, detection limit and
limits of the coverage interval) for measurements of ionizing radiation — Fundamentals and application
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO 80000-10, Quantities and units — Part 10: Atomic and nuclear physics
3 Terms, definitions and symbols
3.1 Terms and definitions
No terms and definitions are listed in this document.
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/
3.2 Symbols
For the purposes of this document, the symbols and designations given in ISO/IEC Guide 98-3,
ISO/IEC Guide 99, ISO 11929 (all parts), ISO 80000-10 and the following shall apply.
Symbol Definition Unit
A Activity of Ac tracer added Bq
α Probability of the false positive decision
β Probability of the false negative decision
227 −1
Activity concentration of Ac measured in the sample Bq∙l
c
A
−1
*
Decision threshold of the measurand Bq∙l
c
A
−1
#
Detection limit of the measurand Bq∙l
c
A
−1
Lower and upper limits of the probabilistically symmetric coverage interval of the Bq∙l

cc,
AA
measurand, respectively
−1
<>
Lower and upper limits of the shortest coverage interval of the measurand, respectively Bq∙l
cc,
AA
−1
 Possible or assumed true quantity values of the measurand Bq∙l
c
A
225 −1
c Activity concentration of Ac tracer solution at the moment of separation Bq∙l
AT
ε Counting efficiency
ε Counting efficiency for the first measurement of the indirect method
ε Counting efficiency for the second measurement of the indirect method
F Bias correction factor for the losses of Rn
Φ Distribution function of the standardized normal distribution; Φ(k p) = p applies
1−γ Probability for the coverage interval of the measurand
Quantiles of the standardized normal distribution for the probabilities p
k
p
(for instance p = 1−α, 1− β or 1−γ/2)
Quantiles of the standardized normal distribution for the probabilities q
k
q
(for instance q = 1−α, 1− β or 1−γ/2)
p, q Probability for the coverage interval
Symbol Definition Unit
Decay constant of the isotope (ex: λ is the decay constant of Po)
λ
Po
m Sample mass kg
m Mass of tracer solution g
ST
Number of counts measured of the background on the alpha spectrum for a given time in
N
0 227
the region of interest of Ac, the measurand.
Number of counts measured of the background on the alpha spectrum for a given time in
N
0T 225
the region of interest of Ac, the tracer.
Number of counts measured on the alpha spectrum for a given time in the region of interest
N
g 227
of Ac, the measurand.
Number of counts measured on the alpha spectrum for a given time in the region of interest
N
T 225
of Ac, the tracer.
p, q Probability for the coverage interval
P Probability of the isotope to decay through alpha particle emission (branching ratio)
α
227 -1
r Background count rate in the region of interest of the measurand ( Ac) s
225 -1
r Background count rate in the tracer region of interest of the tracer ( Ac) s
0T
R Total recovery
R Chemical recovery
c
227 -1
r Gross count rate in the region of interest of the measurand ( Ac) s
g
227 -1
r Net count rate of the isotope to measure ( Ac) s
net
225 -1
r Net count rate of the tracer ( Ac) s
netT
r Net count rate of the tracer ( Ac) for the first measurement of the indirect method
netT(1)
r Net count rate of the tracer ( Ac) for the second measurement of the indirect method
netT(2)
225 -1
r Gross count rate in the region of interest of the tracer ( Ac) s
T
215 215
t Radiological half-life of the isotope (ex: t Po is the radiological half-life of Po) s
1/2 1/2
t Counting time s
t Counting time of the background by alpha spectrometry s
t Time elapsed between separation and counting s
t Sample counting time by alpha spectrometry s
g
U Expanded uncertainty
u Standard uncertainty
Relative uncertainty
u
rel
227 −1
uc Standard uncertainty of the activity concentration of Ac Bq∙l
()
A
−1
 Bq∙l
Standard uncertainty of the estimator c as a function of an assumed true value c of

A A
uc
()
A
the measurand
Standard uncertainty of an estimate of the measurand when the true value is equivalent
#
uc
()
A
to the detection limit
V Sample volume l
−1
w Ratio of activity concentration (c ) on net count rate (r ) (c /r ) l
A net A net
ω Distribution function of the standardized normal distribution
X , X , X , Terms for Formula 13
1 2 3
X , X , Z
4 5
If the results are expressed in mass activity, c is replaced by A and the volume, V, is replaced by the
A
sample mass, m.
4 Principle
Actinium-227 is a naturally occurring radionuclide from the U decay series (see Figure 1). It has a
[8]
half-life of 21,772 ± 0,003 a , which is by far the longest half-life among Ac isotopes. Actinium-227
mainly decays through beta emission (98,58 %) to Th and slightly through alpha emission (1,42 %)
to Fr (calculated based on the sum of alpha probabilities in Reference [8]).
Key
X atomic number (Z)
Y neutron number (N)
Figure 1 — Decay series of U
To determine Ac in water, a water sample of 1 l is collected, filtered, and acidified (see Clause 5).
225 229
The Ac tracer is added to the sample from a Th solution (see Figure 2). Given the relatively short
225 [8] 225 229
radiological half-life of Ac (10,0 ± 0,1d) , it is more practical to add Ac tracer via a Th solution
225 229
of certified activity, which is in radiological equilibrium with its Ac progeny. The parent Th is
separated from Ac during the purification process. Enough tracer is added to obtain a good statistical
precision and be easily distinguished from a blank sample (e.g. 15 mBq).
Key
X atomic number (Z)
Y neutron number (N)
Figure 2 — Decay series of Np
Actinium is preconcentrated by coprecipitation at pH 3,5. The resulting precipitate is dissolved with
an acidic solution. The solution is passed through an extraction chromatography resin (EXC) to purify
Ac from potential interferences. The potential radioactivity interferences for the measurement of Ac
225 2+
and the Ac tracer are listed in Annex A. The main potential chemical interference is Ca , which can
-
precipitate with F and degrade the alpha resolution.
After purification, either a micro-precipitation with lanthanide fluoride or an electrodeposition is
227 227
performed and Ac is measured by alpha spectrometry for 48 h. The activity concentration of Ac is
calculated and reported (see Clause 9).
5 Sampling, handling and storage
Sampling, handling and storage of the water shall be done as specified in ISO 5667-1, ISO 5667-3 and
ISO 5667-10. Guidance is given for the different types of water in References [9] to [16]. It is important
that the laboratory receives a sample that is truly representative and has not been damaged nor
modified during either transportation or storage.
The sample is filtered to remove suspended matter using a 0,45 μm filter. A smaller pore size filter can
also be used, but the filtration can be more tedious and time consuming. The sample shall be acidified
after filtration to a pH ≤ 2 with HNO .
6 Reagents and apparatus
6.1 Reagents
Use only reagents of recognized analytical grade. It is recommended to use acids and bases of trace
metal grade or equivalent (a better purity grade can also be used).
6.1.1 Th standard solution.
−1 −1
6.1.2 Titanium(III) trichloride in HCl solution (e.g. 12 mol∙l HCl), c(TiCl ) = 0,78 mol·l .
−1
6.1.3 Phosphoric acid solution, c(H PO ) = 14,8 mol·l .
3 4
−1
6.1.4 Sodium hydroxide solution, c(NaOH) = 10 mol·l .
−1
6.1.5 Nitric acid solution, c(HNO ) = 15,7 mol·l .
−1
6.1.6 Sodium chloride solution, c(NaCl) = 0,5 mol·l .
−1
6.1.7 Hydrogen peroxide solution, c(H O ) = 8,82 mol·l .
2 2
6.1.8 Ultrapure water, with a resistivity of more than 18,2 MΩ·cm at 25 °C and total organic carbon
−1
less than 1 μgl·l .
−1
6.1.9 Nitric acid solution, c(HNO ) = 2 mol·l .
6.1.10 Chromatographic extraction resin containing diglycolamine, 2 ml cartridge.
−1 −1
6.1.11 Hydrogen peroxide solution diluted in 2 mol∙l HNO , c(H O ) = 0,44 mol·l in
3 2 2
c(HNO ) = 2 mol·l .
−1
6.1.12 Hydrochloric acid solution, c(HCl) = 0,1 mol·l .
6.1.13 Ethanol.
6.1.14 Ac standard solution.
6.2 Apparatus
Usual laboratory equipment including the following:
6.2.1 Vacuum filtration system.
6.2.2 Filters, of pore size 0,45 µm or smaller.
6.2.3 Glass beakers.
6.2.4 Centrifuge.
6.2.5 Multi-hole vacuum box, e.g. 12 positions.
6.2.6 Analytical balance, accuracy 0,1 mg.
6.2.7 Centrifuge tubes (e.g. polypropylene), e.g. 50 ml and 500 ml in volume.
6.2.8 Pipettes.
6.2.9 Hot plate.
6.2.10 Stirring plate.
6.2.11 Magnetic stirrer.
6.2.12 Metal discs with a sticky side.
6.2.13 Alpha spectrometer.
7 Procedure
7.1 Sample preparation
Filter and acidify the samples and a method blank sample prepared with ultrapure water as specified
in Clause 5. A minimum of one method blank sample, which contains the tracer, is required, but several
method blanks can be prepared. It is recommended to prepare spiked samples as well when performing
the method for method validation.
229 225
In a large glass beaker (minimum 1 l), add Th( Ac) (6.1.1) tracer solution by mass, m .
ST
Transfer approximately 1 l of the filtered and acidified sample, V, into the large glass beaker containing
the tracer. Record the volume. Record the sample mass, m, to express the final activity concentration by
sample mass.
−1 −1
Add 0,6 ml of 0,78 mol·l TiCl (6.1.2) and 0,6 ml of 14,8 mol·l H PO (6.1.3). Mix the sample to
3 3 4
homogenize. A stirring plate with a magnetic stirrer is generally used to mix the sample, but the sample
can be mixed by hand with a glass or plastic rod.
7.2 Coprecipitation
−1
Add 14 ml of 10 mol·l NaOH solution (6.1.4) to the sample for pre-pH adjustment and mix.
−1
Adjust the pH to 3,5 using the 10 mol·l NaOH solution (6.1.4) and a pH meter (or alternatively a pH
−1
...