Tiêu chuẩn iso 11665 1 2012

ISO 11665 consists of the following parts, under the general title Measurement of radioactivity in the environment — Air: radon-222: — Part 1: Origins of radon and its short-lived decay

Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1.1 active sampling sampling using active devices like pumps for sampling the atmosphere

Copyright International Organization for Standardization

Provided by IHS under license with ISO

No reproduction or networking permitted without license from IHS

`,,```,,,,````-`-`,,`,,`,`,,` - activity disintegration rate number of spontaneous nuclear disintegrations occurring in a given quantity of material during a suitably small interval of time divided by that interval of time

NOTE 1 Activity, A, is expressed by the relationship given in Formula (1):

A= ⋅λ N (1) where λ is the decay constant per second;

N is the number of atoms.

NOTE 2 The decay constant is linked to the radioactive half-life by the relationship: λ =ln

T 1/2 is the radioactive half-life, in seconds.

3.1.3 activity concentration activity per unit volume

3.1.4 attached fraction fraction of the potential alpha energy concentration of short-lived decay products that is attached to the ambient aerosol

NOTE The sizes of the carrier aerosol to which most of the short-lived decay products are attached are generally in the 0,1 μm to 0,3 μm range of median values.

3.1.5 average activity concentration exposure to activity concentration divided by the sampling duration

3.1.6 average potential alpha energy concentration exposure to potential alpha energy concentration divided by the sampling duration

3.1.7 background noise signals caused by something other than the radiation to be detected

Signals detected in the system can originate from radiation sources either inside or outside the detector, excluding the targeted measurement signals Additionally, electronic defects in the detection system, such as circuit malfunctions or power supply issues, can generate unwanted signals that interfere with accurate measurements Proper identification and mitigation of these signals are essential for maintaining the reliability and precision of the detection system Understanding the distinction between radiation-induced signals and electronic defects helps optimize system performance and ensure accurate data collection.

3.1.8 continuous measurement measurement obtained by taking a sample continuously (or at integration intervals typically in range of 1 min to

120 min) with simultaneous or slightly delayed analysis

NOTE 1 The sampling duration shall be adapted to the dynamics of the phenomenon studied to monitor the evolution of radon activity concentration over time.

NOTE 2 See Annex B for further information.

3.1.9 diffusion length distance crossed by an atom due to diffusion forces before decaying

NOTE Diffusion length, l, is expressed by the relationship given in Formula (3): l= D

D is the diffusion coefficient, in square metres per second; λ is the decay constant per second.

The equilibrium factor ratio measures the potential alpha energy concentration of short-lived radon decay products in a specific air volume relative to their concentration when in radioactive equilibrium with radon This ratio is essential for assessing indoor radon risk, as it indicates the proportion of decay products present compared to the maximum possible when equilibrium is achieved Understanding this factor helps in accurately evaluating radiation exposure from radon decay products in indoor environments.

Radon-222 (222 Rn) decay products in the atmosphere are rarely in radioactive equilibrium with their parent isotope because they are often removed by air renewal systems or trapped on surfaces The equilibrium factor is a critical parameter used to quantify this non-equilibrium state, providing insight into the relationship between radon and its short-lived progeny in a given environment Understanding the equilibrium factor is essential for accurate assessment of indoor air quality and radiation exposure risks related to radon.

NOTE 2 The equilibrium factor is between 0 and 1 The equilibrium factor in buildings typically varies between 0,1 and 0,9, with an average value equal to 0,4 [4][6]

NOTE 3 The equilibrium factor, F eq , is expressed by Formula (4):

E PAEC,222Rn is the potential alpha energy concentration of 222 Rn, in joules per cubic metre;

5 57 10, × − 9 is the potential alpha energy concentration of the short-lived 222 Rn decay products for 1 Bq of

222Rn in equilibrium with its short-lived decay products, in joules per becquerel;

C 222Rn is the activity concentration of 222 Rn, in becquerels per cubic metre.

3.1.11 grab sampling collection of a sample (i.e of air containing radon or aerosol particles) during a period considered short compared with the fluctuations of the quantity under study (i.e volume activity of air)

`,,```,,,,````-`-`,,`,,`,`,,` - guideline value value which corresponds to scientific, legal or other requirements and which is intended to be assessed by the measurement procedure

NOTE 1 The guideline value can be given, for example, as an activity, a specific activity or an activity concentration, a surface activity, or a dose rate.

The detection limit must be compared with the guideline value to determine whether the measurement procedure meets the required standards If the detection limit is smaller than the guideline value, the procedure is considered suitable for the intended measurement purpose This comparison ensures compliance with ISO 11929:2010, confirming that the measurement method satisfies the necessary requirements.

Integrated measurement involves continuous sampling of a specific volume of air to monitor accumulated physical quantities, such as nuclear tracks or electric charges, related to radon disintegration and its decay products This method allows for the collection of data over a set period, which is then analyzed at the end of the accumulation to assess radon levels accurately.

NOTE See Annex B for further information.

3.1.14 long-term measurement measurement based on an air sample collected within a period greater than one month

3.1.15 measurand quantity intended to be measured

A measuring system is a set of one or more measuring instruments, often including other devices and supplies such as reagents, assembled and adapted to provide accurate information for generating measured quantity values These systems operate within specified intervals to ensure reliable measurement of quantities of particular kinds, supporting precise data collection and analysis.

3.1.17 passive sampling sampling using no active devices such as pumps for sampling the atmosphere, whereby in most instruments sampling is performed mainly by diffusion

The potential alpha energy of short-lived radon decay products represents the total alpha energy emitted during the decay process of radon atoms along their decay chain up to lead-210 (210Pb) This measurement is essential for understanding the radiological risk associated with radon exposure, particularly focusing on the decay chain of radon-222 (222Rn) Monitoring the alpha energy emitted during these decay processes helps assess the health hazards posed by radon progeny, which are significant contributors to indoor radiation exposure.

NOTE 1 The potential alpha energy of short-lived 222 Rn decay products, E PAE,222Rn , is expressed by Formula (5):

Po is the alpha particle energy produced by the disintegration of 218 Po, in joules;

E AE,214 Po is the alpha particle energy produced by the disintegration of 214 Po, in joules;

N 218Po is the number of atoms of 218 Po;

N 214Pb is the number of atoms of 214 Pb;

N 214Bi is the number of atoms of 214 Bi;

N 214Po is the number of atoms of 214 Po.

The total alpha energy emitted during the decay of short-lived radon decay products, from their formation through the entire decay chain up to lead-208 (208Pb), is quantified by Formula (6) This calculation encompasses the cumulative alpha particle energy released during the decay process of radon-220 (220Rn) and its progeny, providing crucial insights into radiation exposure and decay chain analysis Understanding this energy emission is essential for assessing radiological risks associated with radon decay products and their impact on environmental and human health.

E PAE,220Rn is the potential alpha energy of 220 Rn, in joules;

E AE,212 Bi is the alpha particle energy produced by the disintegration of 212 Bi, in joules;

N 212Pb is the number of atoms of 212 Pb;

N 212Bi is the number of atoms of 212 Bi;

N 212Po is the number of atoms of 212 Po.

The potential alpha energy concentration of short-lived radon decay products in air is expressed in terms of the alpha energy released during their complete decay to lead isotopes, specifically 210Pb and/or 208Pb This measurement provides a vital indicator of radon progeny activity, reflecting the potential health risk from inhaled radioactive decay products Accurate assessment of these concentrations is essential for evaluating indoor air quality and ensuring compliance with safety standards related to radon exposure.

NOTE The potential alpha energy concentration of the nuclide i, E PAEC, i , is expressed by Formula (7):

E PAE, i is the potential alpha energy of the nuclide i, in joules;

Potential alpha energy concentration (PAEC) exposure is quantified by calculating the integral of potential alpha energy concentration (X PAEC) over the exposure duration, representing the accumulated alpha energy exposure over time This measurement provides a vital assessment of radiation risk during exposure periods The exposure to potential alpha energy concentration (X PAEC) is mathematically expressed by Formula (8), enabling precise evaluation of alpha radiation exposure levels Understanding PAEC exposure helps in ensuring safety standards are maintained in environments with potential alpha particle presence.

E PAEC is the potential alpha energy concentration, in joules per cubic metre; t is the sampling duration, in seconds.

3.1.21 primary standard standard designed with, or widely acknowledged as having, the highest metrological qualities and whose value is accepted without reference to other standards of the same quantity

NOTE The concept of a primary standard is equally valid for base quantities and derived quantities.

3.1.22 radioactive equilibrium of radon-222 with its short-lived decay products state of radon and its short-lived decay products whereby the activity of each radionuclide is equal

NOTE In radioactive equilibrium, the activity of each short-lived decay product decreases over time like the radon activity.

3.1.23 radon emanation mechanism whereby a radon atom leaves the individual particle of solid material in which it has been formed and reaches the free space of pores

3.1.24 radon exhalation mechanism whereby a radon atom produced by emanation and transported (by diffusion or convection) towards the material surface is released from the material into the surrounding medium (air)

3.1.25 radon exhalation rate value of the activity concentration of radon atoms that leave a material per unit time

NOTE 1 The radon exhalation rate under conditions whereby the radon activity concentration at the surface of the material equals zero is called free radon exhalation rate.

NOTE 2 The free radon exhalation rate is approximated from the radon exhalation rate if the radon activity at the surface of the material has a sufficiently low value.

3.1.26 radon surface exhalation rate value of the activity concentration of radon atoms that leave a material per unit surface of the material per unit time

3.1.27 radon mass exhalation rate value of the activity concentration of radon atoms that leave a material per unit mass of the material per unit time

3.1.28 radon exposure integral with respect to time of radon activity concentration accumulated during the exposure time

NOTE Exposure to radon, X, is expressed by Formula (9):

C is the activity concentration, in becquerels per cubic metre. t is the sampling duration, in seconds.

The reference atmosphere for radon and short-lived decay products is a radioactive environment where key influence factors such as aerosols, radioactivity levels, and climatic conditions are well-characterized and controlled This ensures consistent and accurate testing of measurement instruments A precisely defined reference atmosphere is essential for evaluating the performance and reliability of devices used to measure radon levels, supporting compliance with safety standards and improving measurement accuracy in radiation monitoring.

NOTE 1 The parameter values concerned shall be traceable to recognized standards.

3.1.30 reference source radioactive secondary standard source for use in the calibration of the measuring instruments

3.1.31 sampling duration time interval during which the sampling is performed at a given point

A precise sampling plan establishes the spatial and temporal parameters of sampling based on the chosen strategy, outlining aspects such as sampling frequency, sample size, quantities sampled, and the necessary human resources required for the sampling operation This detailed protocol ensures targeted and effective data collection tailored to specific applications.

NOTE See ISO/IEC 17025:2005, 5.7, for further information on sampling plans.

The sampling strategy is a set of technical principles designed to address key issues such as sampling density and the spatial distribution of sampling areas Depending on the specific objectives and site conditions, these principles help optimize data collection for more accurate and efficient results.

NOTE The sampling strategy provides the set of technical options that will be required in the sampling plan.

3.1.34 sensor element of a measuring system that is directly affected by a phenomenon body, or substance carrying a quantity to be measured

`,,```,,,,````-`-`,,`,,`,`,,` - short-lived decay products radionuclides with a half-life of less than one hour produced by radon-222 disintegration ( 222 Rn): polonium-218

( 218 Po), lead-214 ( 214 Pb), bismuth-214 ( 214 Bi) and polonium-214 ( 214 Po)

NOTE Decay products of radon-220 disintegration such as polonium-216 ( 216 Po), lead-212 ( 212 Pb), bismuth-212

( 212 Bi), polonium-212 ( 212 Po) and thallium-208 ( 208 Tl) can interfere with the radon-222 measurement (see Figure A.2).

3.1.36 short-term measurement measurement based on an air sample collected within a period comparable to the duration of the half-life of radon

Spot measurement (ISO 3.1.37) refers to a technique involving a grab sample collected at a specific location within less than one hour This method includes performing an analysis—such as counting particles—either immediately or after a predetermined period, providing precise data on the condition at that particular point in time and space.

NOTE See Annex B for further information.

3.1.38 unattached fraction of E PAEC,222 Rn fraction of the potential alpha energy concentration of short-lived decay products that is not attached to the ambient aerosol

NOTE 1 The particle size concerned is in the order of magnitude of nanometres.

Note 2 highlights that due to the relatively long half-life of 212 Pb, 220 Rn may completely decay before 212 Bi, particularly in some cases This can result in the unattached fraction of short-lived radon-220 decay products becoming undefined when 220 Rn fully disappears prior to the decay of 212 Bi Understanding this decay process is crucial for accurate radon isotopic analysis and exposure assessment.

Symbols

For the purposes of this document the following symbols apply.

A i activity of the nuclide i, in becquerels

C i activity concentration of the nuclide i, in becquerels per cubic metre

C i average activity concentration of the nuclide i, in becquerels per cubic metre

D diffusion coefficient, in square metres per second

E AE, i alpha particle energy produced by the disintegration of the nuclide i, in joules

E PAE, i potential alpha energy of the nuclide i, in joules

E PAEC, i potential alpha energy concentration of the nuclide i, in joules per cubic metre

E PAE, i average potential alpha energy of the nuclide i, in joules

E PAEC, i average potential alpha energy concentration of the nuclide i, in joules per cubic metre

N i number of atoms of the nuclide i

T 1 2 / , i radioactive half-life of the nuclide i, in seconds t sampling duration, in seconds

U expanded uncertainty calculated by U k u= ⋅ ( ) with k = 2 u ( ) standard uncertainty associated with the measurement result

V sampled volume, in cubic metres

X exposure to radon, in becquerel-hours per cubic metre

X PAEC potential alpha energy concentration exposure, in joule-hours per cubic metre

The primary measurement result of the measurand y provides the foundational data for analysis, while the decision threshold determines the minimum detectable level of y The detection limit of the measurand indicates the smallest quantity that can be reliably identified, whereas the confidence interval boundaries—lower and upper limits—offer statistical bounds for the measurement's accuracy Exhalation rates, expressed in becquerels per square meter per second, include the total exhalation rate (φ), free exhalation rate (φf), mass exhalation rate (φm), and surface exhalation rate (φs) Additionally, the decay constant (λi), measured in per second, characterizes the rate at which a specific nuclide, i, undergoes radioactive decay.

The measurement methods outlined in ISO 11665 focus on sampling a representative volume of air from the atmosphere under investigation, ensuring accurate detection of radon levels These methods involve detecting radiation emitted from the successive radioactive disintegrations of radon isotopes and their decay products Implementing these techniques provides reliable, precise measurements crucial for assessing radon concentrations in various environments.

NOTE Examples of results for radon activity concentration measurements are given in Annex B.

Equipment used for measurement must be specifically suited to each method and is detailed in the different sections of ISO 11665 Additionally, all measurement equipment should comply with the standards outlined in IEC 61577-1, IEC 61577-2, and IEC 61577-3 to ensure accuracy and consistency.

General

Selecting the appropriate sampling method depends on the specific site being investigated, such as mines, outdoor environments, houses, public buildings, or workplaces It also hinges on the intended use of the data and the expected level of radon activity concentration Proper method selection ensures accurate assessment of radon levels for health and safety purposes.

Radon activity concentration and the potential alpha energy concentration of its decay products can fluctuate significantly over time, exhibiting variations greater than one order of magnitude at the same location These fluctuations mean that measurement results are heavily influenced by the sampling duration, which can range from just a few minutes to several hours or even months, as well as the specific sampling date.

Extrapolating an average radon activity concentration from a specific sampling duration and time to a different period requires understanding the Radon activity concentration variability over that timeframe Without accurate knowledge of this variability, the uncertainty can become too significant, rendering the extrapolation unreliable for the intended measurement objectives.

Choosing an appropriate sampling method, duration, and sampling time is crucial to align with the measurement objectives and the desired level of accuracy Short-term sampling results should be interpreted cautiously, as they may not fully represent the area's overall conditions Ensuring compatibility between sampling strategies and measurement goals enhances data reliability and validity.

Effective sampling strategies are essential for achieving specific research objectives, as they influence critical decision-making processes The choice of sampling approach depends on the desired outcome and directly impacts the quality and reliability of the results Carefully selecting the appropriate sampling method is crucial, as it can lead to significant savings in time and resources while ensuring meaningful insights Different strategies may be employed based on whether the goal is accuracy, representativeness, or efficiency, making strategic planning vital for successful data collection.

Accurate interpretation of radon activity concentration and potential alpha energy concentration measurements depends on using a representative air sample An effective sampling strategy should include analyzing historical site data, conducting site reconnaissance—potentially utilizing portable radioactivity detectors—identifying migration pathways and accumulation areas, and thoroughly assessing the site relevant to the sampling process.

The implementation of this strategy, which also includes the definition of the data quality objectives according to the parameters to be analysed, gives rise to the sampling plan.

The sampling plan shall define the operations to be carried out as defined in ISO/IEC 17025.

Sampling objective

The objective of the sampling is to provide sufficient representative samples in order that the measurement results comply with their intended use.

Sampling characteristics

The sampling can be either active or passive.

For accurate environmental radon and decay product measurements, it is essential to specify the sampling details, including the date, time, duration, and location Additionally, whether the sampling method is active or passive should be clearly indicated to ensure data reliability.

The sampling characteristics relating to each measurement method of radon and its decay products are described in the various parts of ISO 11665.

Sampling conditions

Sampling locations shall be distributed outside the building taking into account the following parameters: topography, prevailing winds, activity zones (urban, manufacturing, agricultural and domestic) and potential release points.

For accurate air quality sampling, the sampling site must be in an open area that accurately represents the environment to be measured Natural and artificial obstacles, excluding weather shelters, should be positioned outside an inverted cone with a 140° opening at the top, with the sampling point at the tip, and outside a 1-meter diameter sphere centered on the sampling location The recommended sampling height is between 1 and 2 meters above the supporting surface to ensure representative data Additionally, the sampling installation must be designed to avoid disturbing the surrounding atmosphere, ensuring accurate and reliable air quality measurements.

3 sphere free of obstacles (1 m in diameter)

Figure 2 — Example of diagram of a sampling place outside a building

The selection of sample sizes and their specific locations within a building depends on the purpose of the measurement, such as initial investigations, radioactive source detection, radionuclide transfer studies, verifying homogeneity of environmental parameters, or identifying anomalies.

`,,```,,,,````-`-`,,`,,`,`,,` - space, basement, multiple storeys, earthen floor, building materials, etc.), the room characteristics and also the measuring equipment used (see ISO 11665-8).

The sampling duration can vary from a few minutes to a few hours or several months.

Sampling duration should be selected based on the specific用途 of the measurement results, considering the significant variability in radon activity concentration and potential alpha energy concentration over time and across different locations (see Annex A).

Table 1 — Sampling duration based on type of sampling

Usual sampling duration Characteristics of the measurement result

Spot Grab Less than one hour

Representative only of the activity concentration at a given moment and a given point

Monitoring radon activity concentration at specific sampling points provides valuable insights into its temporal variation To accurately assess these fluctuations, sampling duration and integration intervals must align with the dynamics of the radon activity changes Properly designed sampling protocols are essential for reliable data collection and effective radon monitoring.

Integrated short-term Few days Representative of the mean value of the activity concentration during the sampling at a given point

Integrated long-term Several months

Estimation of the annual mean value of activity concentration at a given point This measurement is often used to assess human radon exposure

For accurate active sampling, the air volume collected must be measured using a flow-meter calibrated for temperature and pressure The measurement should be expressed in cubic meters at standard conditions of 1,013 hPa and 0 °C to ensure consistency and reliability Proper correction for environmental factors is essential for precise air sampling results.

For passive sampling, the direct measurement of the air volume sampled is not needed as a calibration factor, in activity per unit volume, is used to compute the activity concentration.

Seven different types of detection can be used See 7.1 to 7.7.

Silver-activated zinc sulphide ZnS(Ag) scintillation

Electrons in scintillating media like ZnS(Ag) emit light photons when they return to their ground state after being excited by alpha particles This scintillation process enables the detection of radiation, as the emitted photons can be efficiently captured using photomultiplier tubes Utilizing ZnS(Ag) as a scintillator is common in radiation detection systems due to its high light yield and effective photon emission upon particle interaction.

This is the principle adopted for scintillation cells (such as Lucas cells [12] ) used for radon spot measurement.

ZnS(Ag) scintillation may also be used to detect radon decay products collected on a filter[13][14][15][16].

NOTE This detection principle is occasionally used for continuous sampling [17]

Gamma-ray spectrometry

The radon, adsorbed on activated charcoal encapsulated in a container[18][19][10], is determined by gamma-ray spectrometry of its decay products ( 214 Bi and 214 Pb) after their equilibrium is reached [20]

Liquid scintillation

Radon levels are measured by adsorbing the gas onto activated charcoal within a vial, followed by the addition of a scintillation cocktail The detection process involves counting alpha and beta particles emitted by radon and its decay products, including 218 Po, 214 Bi, and 214 Pb, providing accurate assessment of radon concentration.

214Po) after their equilibrium is reached [21]

Air ionization

When traveling through the air, alpha particles generate tens of thousands of ion pairs, which can produce a measurable ionization current under specific conditions This low-level current is detected using an ionization chamber, enabling the assessment of radon and its decay products' activity concentration When sampling occurs through a filtering medium, only radon diffuses into the ionization chamber, and the resulting signal directly correlates with the radon activity concentration, ensuring accurate measurement of indoor radon levels [22][23].

Semi-conductor (alpha detection)

A semiconductor detector, such as one made of silicon, detects alpha particles by converting their energy into electric charges These charges generate pulses whose amplitudes are directly proportional to the energy of the emitted alpha particles from radon and its short-lived decay products This precise energy conversion enables accurate detection and measurement of radon decay emissions.

NOTE This detection principle is occasionally associated with electrostatic precipitation of the alpha emitter isotopes.

Solid-state nuclear track detectors (SSNTD)

An alpha particle induces ionization in polymer nuclear detectors like cellulose nitrate, leaving behind ionization tracks Since ion recombination is incomplete after the particle's passage, proper etching serves as a developing process that reveals these tracks The resulting etching holes or cones directly correlate with the number of alpha particles that have passed through the detector, enabling quantification of alpha radiation exposure.

Discharge of polarised surface inside an ionization chamber

A PTFE disc with a positive electric potential is placed inside a plastic conductive ionization chamber of specific volume, creating an electrostatic field that attracts ions produced from radon decay As these ions are collected on the disc, its electric potential decreases proportionally to the radon activity concentration An electrometer continuously measures this potential change, providing a direct indication of radon levels during exposure.

Methods

Sampling duration is crucial for achieving measurement accuracy and the desired uncertainty Measurement methods can be categorized based on the sampling phase: spot measurement, continuous measurement, and integrated measurement The integrated measurement method provides average activity concentrations of radon-222 or potential alpha energy over periods from days to a year, making it suitable for assessing long-term human exposure to radon and its decay products.

Radon activity concentration in the environment, public buildings, homes, and workplaces varies based on ventilation and meteorological conditions, affecting indoor air quality The spot measurement method provides quick, localized assessments of radon levels, typically within a few minutes, by measuring radon activity concentration or the potential alpha energy of short-lived radon decay products in both open and confined atmospheres.

Choosing the appropriate measurement method depends on the specific objectives and intended use of the results The ISO 11665 series provides detailed guidance on measurement techniques, sampling procedures, and detection methods, which are outlined in Table 2.

Table 2 — Characteristics of the measurement methods described in ISO 11665

Charac- teristic Type Ionization chamber

Integrated short-term ISO 11665-4 ISO 11665-4 ISO 11665-4

Integrated long-term ISO 11665-4 ISO 11665-4 ISO 11665-4 a Measurement method: radon decay products. b Measurement method: exhalation rate.

Influence quantities

Measurement bias can arise from various factors such as temperature during sampling, humidity affecting the sampling device’s capacity, atmospheric turbulence, and air flow-rate, all of which influence the accuracy of results Proper control of these quantities, as outlined in IEC 61577-1, is essential for reliable measurements Additionally, detector storage conditions prior to sampling, stability of the system during measurement, sample conservation and storage, and fluctuations in radon activity concentration or short-lived decay products can impact data quality Monitoring radon decay product concentrations during measurement is also critical to ensure the validity of radon isotope assessments.

The detection process must account for various factors that impact measurement accuracy, including the presence of gaseous radionuclide emitters such as radon isotopes and their decay products emitting alpha, beta, or gamma radiations within the detection volume Additionally, background radiation levels during measurement and the inherent background and its fluctuations of the measurement equipment over time are critical considerations Ensuring these elements are properly managed helps achieve precise and reliable radiological assessments.

Calibration

Equipment calibration is essential for accurately relating measurement variables, such as current and counting rate, to the activity concentration of radon and its decay products in the air This process involves using reference radioactive sources or reference atmospheres with controlled radon activity levels to ensure precise detection and measurement Proper calibration guarantees reliable radon monitoring, critical for ensuring safety and compliance in environmental and occupational health contexts.

Instrument calibration must ensure traceability of measurement results to a primary standard; when a primary standard is unavailable, a reference atmosphere from the international comparison database is used, as outlined in IEC 61577-4.

Quality control

Measurement methods shall be selected and associated procedures performed by suitably skilled staff under a quality assurance and quality control programme.

Confidence in the measurement results is maintained by regular use of certified reference materials and participation in interlaboratory comparisons and proficiency testing (see ISO/IEC 17025).

Laboratory procedures shall ensure that laboratory and equipment contamination as well as sample cross- contamination is avoided.

This article outlines that the evaluation models for the measurand, along with the associated standard uncertainties and characteristic limits, are calculated following international standards such as ISO/IEC Guide 98-3 and ISO 11929 Additionally, the detailed procedures for these calculations are provided in the various parts of ISO 11665, tailored to each measurement method described Ensuring compliance with these standards guarantees accurate and reliable measurement results for the measurand across different scenarios.

The test report must adhere to ISO/IEC 17025 standards and include essential details such as the specific section of ISO 11665 utilized, the measurement method employed (spot, integrated, or continuous), and comprehensive sample identification It should specify the sampling characteristics (active or passive), the exact sampling date and time, the duration of sampling, and the sampling location Results must be expressed in appropriate units, and the report should present the test outcomes with their associated uncertainties—either y u y± or y U ±—along with the corresponding k value, ensuring clarity and compliance with international testing standards.

Complementary information may include the purpose of the measurement, the probabilities α, β, and (1-γ), and the decision threshold and detection limit Depending on customer requirements, results can be presented through various methods to ensure clarity and effectiveness.

1) when the measurand is compared with the decision threshold (see ISO 11929), the result of the measurement shall be expressed as ≤y * if the result is below the decision threshold;

When measuring a measurand below the detection limit, the result should be expressed as ≤y # If the detection limit exceeds the guideline value, it must be documented that the method is unsuitable for the measurement purpose Additionally, any relevant information that could impact the results should be reported to ensure accurate interpretation and compliance with measurement standards.

1) weather conditions at the time of sampling;

2) ventilation conditions for indoor measurement (mechanical ventilation system, doors and windows open or shut, etc.).

10.3 The results can be expressed in a similar format to that shown in Annex C.

Radon and its decay products — General information

Radon is a naturally occurring element with three isotopes produced by radionuclides in the earth's crust, with their proportions depending on the geological composition of the subsoil, specifically the levels of uranium-235, uranium-238, and thorium-232 The abundance of these isotopes is influenced by the relative concentrations of these parent elements in the soil and their radioactive half-lives, as illustrated in Figures A.1, A.2, and A.3 Understanding the variation in radon isotope levels is essential for assessing indoor air quality and radiation exposure risks associated with different geological formations.

Radon-222, a decay product of uranium-238, is less prevalent in the atmosphere compared to radon-220, present at levels 100 times lower on average Despite its lower concentration, radon-222 is the most common isotope found in the air because its relatively long half-life of approximately 3.82 days allows it to escape from the rocks and soil where it originates, migrating into the atmosphere.

Radon-220 (thoron), a decay product of 232 Th, is the most abundant of the three isotopes released by the soil

It disappears very quickly due to its short radioactive half-life (55,8 s).

Radon-219 (actinon), a decay product of uranium-235, is the rarest of the three isotopes due to its extremely short half-life of just 3.96 seconds, making it virtually undetectable in the atmosphere and groundwater The uranium-235 content in rocks and soil is approximately 0.73% of uranium-238, contributing to the formation of radon isotopes, although radon-219’s presence remains minimal due to its rapid decay.

The abundance of these isotopes can vary in some manufacturing sites.

The decay constant (λ) of radon-222 is 2,1 × 10 −6 s − 1 , with 1,25 × 10 −2 s − 1 for radon-220 An activity of 1 Bq (one disintegration per second) corresponds to 476 600 radon-222 atoms and 80 radon-220 atoms.

In ISO 11665, only radon-222 is considered.

Figure A.2 — Thorium-232 and its decay products [1]

Figure A.3 — Uranium 235 and its decay products [1]

A.2 Changes in radon activity concentration

Radon primarily originates from the Earth's crust, produced by the decay of radium atoms present in soil minerals The amount of radon-222 generated is directly proportional to the radium-226 content in the soil Most radon atoms remain trapped within the mineral's crystalline structure, with only a small fraction escaping into the atmosphere Emanation rates of radon vary significantly depending on soil properties such as porosity, grain size, and humidity, ranging from mere tenths of a percent to higher levels Understanding these factors is essential for assessing radon risk in indoor and outdoor environments.

Radon-222 atoms, once released from the soil lattice, are transported through air or groundwater via diffusion and convection, affecting indoor and outdoor radon levels The activity concentration of radon in soil varies significantly with vertical gradients and temporal changes influenced by weather conditions and intrinsic soil properties such as permeability and porosity Understanding these factors is essential for assessing radon mobility and potential health risks.

A.2.2 At the soil-atmosphere interface

Radon-222 surface exhalation rate, which measures the amount of radon reaching the open air per unit time and surface area, is influenced by soil radon activity concentration and weather conditions This rate typically increases with soil humidity up to around 80%, but decreases as atmospheric pressure rises Additionally, when the ground is covered with snow, water, or is frozen, radon exhalation significantly diminishes, reducing radon release into the environment.

The exhalation rate is a very useful explanatory parameter, as it is controlled by soil characteristics and weather conditions [31]

Radon dispersion in outdoor air is influenced by atmospheric diffusion conditions, which depend on local meteorology and topography Typically, a vertical gradient in radon activity concentration and daily fluctuations are observed, with higher dispersion during the day leading to lower radon levels Conversely, at night, temperature inversions reduce atmospheric dispersion, causing radon to accumulate near the ground and increase activity concentrations by a factor of 10 to 100 These patterns highlight the importance of considering atmospheric conditions when assessing radon levels outdoors.

Figure A.5 — Example of time variation of outdoor radon activity concentration [33]

Radon primarily emanates from the ground in contact with buildings and, to a lesser extent, from certain building materials In some cases, tap water—especially when sourced from wells in granitic terrains—can contain high radon levels, making degassing a significant exposure source Additionally, outdoor atmospheric radon levels vary by region and can contribute to indoor radon concentrations.

Indoor radon activity concentration may vary significantly in time and space (see Figures A.6, A.7 and A.8) for various reasons including:

— characteristics of the buildings, such as type of basement (presence of crawl space, cellar, earthen floor, etc.), number of storeys, transfer pathways between levels (pipe work, staircase, etc.);

— the radium content and texture of the ground in contact with building slabs and walls;

— the decreasing/increasing pressure gradient from the outside to the inside;

— the fresh air supply rate depending on the degree of ventilation, the building permeability and occupants’ lifestyle.

Radon activity concentration tends to be higher indoors compared to outdoor air due to limited air exchange rates, resulting in accumulation inside buildings Additionally, a daily fluctuation in radon levels is sometimes observed, reflecting changes in environmental conditions and building ventilation patterns.

Due to higher indoor radon activity concentration, the radon exposure process of occupants is assessed as illustrated in Figure A.10.

Figure A.6 — Example of indoor radon activity concentration over a period of 24 hours (Sweden) [34]

Figure A.8 — Example of variations between monthly averages of radon activity concentration at two different sites less than 1 km apart [36]

Figure A.9 — Example of changes in radon activity concentration in a house: a natural ventilation effect is revealed [37]

222 Rn activity concentration on ground surface

222 Rn exhalation rate on ground surface

Indoor 222 Rn activity concentration (confined space)

A.3 Short-lived radon-222 decay products

Radon-222 disintegrates in air, successively producing polonium-218, lead-214, bismuth-214 and polonium-214 atoms (see Figure A.1), which take the form of sub-micrometric particles in the atmosphere.

Aerosol particles containing polonium-214 can be inhaled, but due to its very short radioactive half-life of 165 seconds, it does not reach the lungs In contrast, the decay products with longer half-lives can penetrate deep into the respiratory system These particles disintegrate within the lungs, releasing lead-210, which poses health risks Understanding the behavior of these radioactive decay products is essential for assessing inhalation hazards associated with polonium.

Polonium-218 releases an alpha particle with an energy of 6.002 MeV as it transforms into lead-214, initiating a decay chain that includes bismuth-214 and polonium-214 through beta disintegration Subsequently, polonium-214 emits another alpha particle with an energy of 7.69 MeV, resulting in lead-210, which has a longer half-life of 22.23 years The total potential alpha energy of the polonium-218 atom is the sum of these two alpha emissions, amounting to 13.692 MeV (2.19 × 10⁻¹² J), representing the maximum energy released during decay The potential alpha energy of each lead-214 and bismuth-214 atom is approximately 1.23 × 10⁻¹² J (7.69 MeV), which corresponds to the energy transferred to lung tissue if these atoms are inhaled, highlighting the health risks associated with inhaling radon decay products.

For 1 Bq of radon-222 in equilibrium with its short-lived decay products, the potential alpha energy of the short- lived radon-222 decay products is equal to 5,57 × 10 −9 J (see Table A.1).

Table A.1 — Potential alpha energy of short-lived radon-222 decay products [1][57]

Short-lived radon-222 decay products Half-life

Potential alpha energy per atom per activity unit

Total in equilibrium per becequerel of radon-222

Tiêu đề	Measurement of Radioactivity in The Environment — Air: Radon-222 — Part 1: Origins of Radon and Its Short-Lived Decay Products and Associated Measurement Methods
Trường học	International Organization for Standardization
Chuyên ngành	Measurement of Radioactivity
Thể loại	standard
Năm xuất bản	2012
Thành phố	Geneva

Định dạng
Số trang	38
Dung lượng	2,21 MB