Radiation Environment and Medicine 2022 Vol.11, No.2 41–49

Review

An Overview of Passive-Type Detectors for Radonand Its Progeny Measurement
Worawat Poltabtim1, Chutima Kranrod2 and Shinji Tokonami2*
1

Department of Radiation Science, Graduate School of Health Sciences, Hirosaki University, 66-1 Hon-cho, Hirosaki, Aomori 036-8564, Japan
2
Institute of Radiation Emergency Medicine, Hirosaki University, 66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
Received 28 December 2021; revised 26 May 2022; accepted 8 June 2022

Radon is well known as a radioactive gas, and the inhalation of radon and its progeny could lead tohealth risks, especially inducing carcinogenesis that potentially generates lung cancer. Therefore,
it is essential to monitor concentrations of radon and its decay products to estimate the radiologicalhazards and risks to human health. In this paper, numerous studies on passive techniques forradon and its progeny have been reviewed and summarized. The mainstream of passive devices
can be classified into four groups: (i) alpha track detectors, (ii) activated charcoal detectors,(iii) electret ion chambers, and (iv) thermo-luminescent dosimeters. The principle of passive
devices, materials, designs, and the factors affecting their performance are discussed. This review
aims to provide options and understanding of the passive techniques for radon and its progeny
measurement, which have been developed for radiation protection and surveillance of radon andits progeny in various environments.
Key words: passive radon detector, radon, radon and its progeny, radon measurement

1. Introduction
Radon (Rn-222) is a naturally occurring radioactive gas
and a transient product of the uranium (U-238) decay
series. As a noble gas, radon can easily diffuse throughsoil and rocks from the earthʼs crust into the air andtends to concentrate in the atmosphere, enclosed spaces,and environments1). Radon has a half-life of 3.82 days,
and its decay produces and emits other short-lived
radionuclides with alpha particles and beta rays2). The
decay products of radon or radon progenies can adhere
to dust and aerosol and deposit in the lungs and airways
when inhaled. Radon and its progeny continue to emit
*Shinji Tokonami: Institute of Radiation Emergency Medicine, Hirosaki University,
66-1 Honcho, Hirosaki, Aomori 036-8564, Japan
E-mail: tokonami@hirosaki-u.ac.jp
https://doi.org/10.51083/radiatenvironmed.11.2_41
Copyright © 2022 by Hirosaki University. All rights reserved.

intensely ionizing alpha particles and beta rays, affecting
biological cells in the lungs, leading to DNA damage andinducing carcinogenesis that potentially generates lungcancer3). The World Health Organization (WHO) has
identified radon and its progeny as the second largest risk
factor for the cause of lung cancer only after smoking
in the general population4). Approximately 50% of theworldʼs average annual effective dose to the human by
natural radioactivity has been recognized due to internal
exposure to radon progeny5). Therefore, it is vital tomonitor concentrations of radon and its products in theenvironment to estimate the radiological hazards andrisks to human health.
Most techniques of measuring radon and its progeny
are based on the measurement of the alpha particles
emitted from the radionuclides during their radioactive
decay. Techniques for measuring radon and its progeny
can be classified as active or passive method. The active

42

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49

methods are usually used for short-term measurementsof radon, and require power to function under inspection
for investigations of individual sites. On the other
hand, the passive methods generally do not require
power to function, and are more suitable for long-term
measurements and large-scale surveys6). The radon andits decay product in air typically enter those passive
detectors via diffusion, and the radiation detector medium
itself normally does not require any power supply.
This paper aimed to propose an overview of passivetype monitoring techniques for measuring radon andits progeny, namely alpha track detectors, activatedcharcoal canisters, electret ion chambers, and thermoluminescent dosimeters. Special attention needs to be
paid to the application and conceptual design descriptionof mainstream technologies, such as types of detectors,
sample collection strategies and measurement techniques.
2. Properties of Radon and Its Progeny
Radon is a naturally radioactive inert gas, and it has 36
known isotopes, ranging from Rn-193 to Rn-228. The mostmentioned three radioisotopes are Rn-222 (radon), Rn220 (thoron), and Rn-219 (actinon) and are decay productsof U-238, Th-232, and U-235, respectively. Among thesethree isotopes, Rn-222 is most present in the environment
due to the abundance of U-238 in nature and its longest
half-life (3.82 days). Therefore, if radon was mentioned
without isotopes specification, it usually means Rn-222.
In the radioactive decay series of radon, mainly threegroups of emitting alpha particles that alpha detectors
may detect are considered, namely, those that emit alphaparticles with energies of 5.49 MeV from Rn-222, thosewith most energies of 6 MeV from Po-218, and otherswith energies of about 7.69 MeV from Po-214. Whenradon and its progeny are inhaled, the primary result ofradiation dose to the lung is not due to radon itself but
due to some of radonʼs short-lived decay products (mainly
Po-218 and Po-214) are retained in the lungs and irradiate
cells in the respiratory tract with alpha-particles before
they have been expelled from the lung.
The short-lived radon progeny concentrations arecollectively expressed as Potential Alpha Energy
Concentration (PAEC) or Equilibrium Equivalent Radon
Concentration (EERC). These two quantities combine
the radon progeny concentrations into a single value
using weighting factors that consider the progeniesʼ
half-lives and alpha energies emitted. The historical unit
called the Working Level (WL) was proposed to PAECof radon progeny in air. Originally, one WL refers to theconcentration of the short-lived decay products of radonin equilibrium with 3700 Bq m-3 (100 pCi L-1) of EERC thatwill result in the ultimate emission of 1.3 x 105 MeV ofpotential alpha energy7). The International System (SI)

unit for PAEC is J m-3, one WL is equivalent to 20.8 µJ m-3.
The SI unit for EERC is Bq m-3. A PAEC in the unit of 1
WL corresponds to EERC about 3700 Bq m-3.
3. Passive Measurement Techniques
3.1. Alpha track detectors
Alpha Track Detectors (ATDs) are also called Nuclear
Track Detectors (NTDs) or Solid-State Nuclear Track
Detectors (SSNTDs). These detectors work on a principleof alpha particles emitted from radon and some of its
progeny, creating microscopic damages to the detectormaterials and resulting in latent tracks. The tracks
can be visualized under an optical microscope througha chemical or electrochemical etching process8). The
track density is proportional to the radon concentration
accumulated over the exposure period. The most popularmaterials employed for ATDs are polymeric plastics, suchas poly-allyl diglycol carbonate (also known under the
trademark as CR-39), cellulose nitrate (commercially wellknown as LR-115), and polycarbonate (e.g., Makrofol)9).
Generally, a minimum detectable concentration of ATDs
was found about 30 Bq m -3 or lower, for a month of
exposure. And there is typical uncertainty of 10-25%4).
The possibility of using ATDs for nuclear applications
was first introduced by Fleischer et al. in 196510). After
that, many studies proposed using track detectors forlong-term monitoring of radon and its progeny11-13). In
general, track detectors used for radon monitoring in theatmosphere can be categorized into two main modes:
open/bare detector mode and close detector mode.
In the case of the open/bare detector mode, ATDs
are open-faced without a filter or barrier and directly
exposed to alpha particles present in the air. Alphaparticles emitted by radon and all radionuclides in theambient atmosphere can damage the track detectors andproduce latent tracks in them. Therefore, the resulting
measurement from the open detector is related to radon
concentration, radon progeny concentrations, as well as
to other alpha-emitting radionuclide concentrations14).
Thus, this technique is not very suitable for measuring
radon only. The information from the open detectors does
reveal the concentrations of radon and its progeny in the
air. Unfortunately, this measurement mode has significant
uncertainties because the calibration factor (k) depends
on the equilibrium factor (F) between radon and its
progeny15). In the past, the radiation dose quantities due toexposure to radon and its progeny have been commonly
estimated using the typical assumed equilibrium factor
value of 0.4 for the indoor environment, as recommended
by the United Nations Scientific Committee on the Effectsof Atomic Radiation (UNSCEAR)5). However, in reality,
the value of F varies widely with meteorological andenvironmental conditions, such as ventilation, humidity,

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49

time, place, etc.16-18). Therefore, using an assumed constantvalue for F does not always reflect the actual conditions.
Moreover, thoron (Rn-220) and its decay products caninterfere with open/bare detectors, which may cause
an overestimation of derived radon concentrations. At
the same time, radon progeny can be deposited onto thesurface of ATD materials, especially in the case of CR39. This radon progeny deposition process is called “plateout,” and alpha tracks from the plate-out radon progeny
are usually larger than those produced by alpha particles
in the air. So, the accuracy of radon measurements will beaffected significantly by the overlap of alpha tracks.
The closed detector mode is proposed to avoid theentry of radon decay products present in the ambient
atmosphere. The A TD materials are positioned at
different places inside the container, with the open end
covered by a filter or barrier to prevent radon and thoron
decay products from entering the sensitive volume ofthe devices. Consequently, the number of tracks on thedetector is related only to alpha particles originatingfrom radon entering the sensitive volume of thecontainer as well as its progeny formed in the container.
Therefore, the closed detector mode has solved somemajor problems related to the open detector mode andcan provide measurements related to the actual radon
concentration in the air. However, many factors affect thestability of ATD detection response, including humidity,
temperature, presence of oxygen, thoron activity
concentration, deposited progenies, diffusion rate, andelectrostatic charges on the detector surface, especiallyultraviolet radiation can hardly affect the measurement inclosed detector mode19-21).
Several designs of containers or chambers have beendeveloped and are used to improve the efficiency andaccuracy of radon measurement. Studies dealing with thefilters to protect radon detectors measuring in extreme
environmental conditions have also been published20, 22, 23).
(A)

For example, Bochicchio et al.24) used a sealed polyethylene
bag to enclose the radon concentration measurement
device (LR-115 detectors), which prevented the entranceof dust, humidity, and radon decay products. It also
reduced thoron from entering the device to reduce
the uncertainty of radon concentration measurement.
Regarding shape, the containers can be cylindrical,
conical, hemispherical, or rectangular. Some containers
are equipped with more than one piece of A TD.
Furthermore, a closed detector, which is covered with thepolyethylene membrane to permit only radon to enter thedetector and prevents thoron, radon progeny and dust,
and an open detector, which was exposed freely to radon
as well as radon progeny are occasionally used together
for the determination of F. In this method, F can be foundas a function of the track density ratio (D/D0) between
open detector (D) and closed detector (D0), respectively25).
However, the bare mode or open detectors are notrecommended to use in the high thoron areas or highconcentrations of thorium. Some researchers reported
the higher values of indoor radon concentrations in
the bare mode study were mainly due to interferenceof thoron and its decay products in the environment26).
Many of the nationwide surveys were carried out
with radon concentration measuring devices in the
single closed chamber. Examples of such devices usedin nationwide surveys are the NRPB/SSI type (firstdeveloped by the National Radiation Protection Board andwas subsequently improved by the Swedish Radiation
Protection), which had been used in Albania 27) and
Sweden28), and the Karlsruhe type detectors were used inAustria29), Germany30) and Luxembourg31).
As ATDs cannot separate radon and thoron signals, a
two-chamber design measurement system is widely used
to separate various radon and thoron measurements.
Sahoo et al.32) developed a type of two-chamber device
based on a pinhole design (Fig. 1(A)) for radon/thoron(B)

Gas entry▶

▶

Pin holes
SSNTD Film holder▶ Central disc▶

10

Radon chamber

10

Upper view

Radon + Thoron
chamber▶
▶

▶

Electro-conductive
spongeGlass fibre
filter paper

▶

43

CR-39

59.4Φ
49Φ
32.2 26
Side view
Electro-conductive sponge
CR-39

SSNTD Film holder
Section view
Electro-conductive sponge

Fig. 1. (A) Pinholes based radon-thoron measurement device32), and (B) Raduet device33).

44

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49

discriminative measurement. By using a diffusion barrier,separate measurements can be made of radon and thoron
because of the different entry rates of radon/thoron
through two chambers. So, when air diffuses through afilter, cutting off the aerosol component into the upper
chamber, alpha particles of radon, thoron, and theirprogenies are detected with ATD. Air enters the lower
chamber through the pinholes as a diffusion barrier, andnearly only radon permeates.
Another example of a two-chamber design, called
Raduet, proposed by Tokonami et al.33), is shown in Figure1(B). Using CR-39 as detector material, the primarymeasurement principle remains almost the same as thepinhole-based device with the different air diffusion rates
into two-chamber. However, the design was somewhatchanged as chambers were separated. Specialty plastic
and sponge were respectively used as the wall chambers
and hole filters to eliminate electrostatic effects, which
influenced the distribution of charged progenies.
Recently, the decay products of radon and thoron were
widely measured using the direct radon progeny sensors(DRPS) and direct thoron progeny sensors (DTPS)
method of passing alpha particles through appropriate
absorber materials34-36). This method uses absorbermounted ATD, which selectively records the tracks
due to alpha emissions at different energies from radon
and thoron progeny. For example, Po-212 with alphaenergy 8.78 MeV and Po-214 with alpha energy 7.69 MeV
from the deposited atoms of thoron and radon progeny,
respectively.
After exposure period, latent tracks in the ATDs
can be made visible for easily counting by a chemical
etching with alkaline solutions of sodium hydroxide(NaOH) or potassium hydroxide (KOH). The mainetching parameters, that can affect etching results aretemperature, etchant concentration, and etching time.
Daci et al.37) examined several etching conditions of CR39 to determine optimal etching condition. For the track
density counting, ATDs can be measured with different
systems. For example, detectors can be counted with an
optical microscope and are manually or automaticallycounted, or they can be counted with a non-opticalsystem, such as a spark-counter38).
3.2. Activated charcoal detectors
The Activated Charcoal Detector (ACD) technique is
widely used to measure radon concentrations for a shortterm survey, typically 2-7 days, to provide rapid andcost-effective results. At this survey period, a minimum
detectable concentration was calculated and shownaround 20 Bq m -3, and typical uncertainty 10-30% 4).
Regarding the measurement principle, activated charcoal
is used to adsorb and desorb radon by the active sitesof the carbon particles. During the exposure period,

radon is being adsorbed to carbon particles and it isundergoing radioactive decay from radon decay. After
ACDs are closed more than three hours, radioactive
equilibrium of radon and its progeny is reached.
Radon activity is measured via its progeny activity atthe equilibrium point. Bi-214 and Pb-214 are typicallydetected by gamma spectrometers due to their gammalines39). Commonly, NaI(Tl) detectors and High Purity
Germanium (HPGe) detectors are used. For this process,three gamma energy peaks are typically analyzed at 295
keV and 352 keV for Pb-214 photons and 609 keV for Bi214 photons. Furthermore, radon absorbed on the ACD
can be measured by the liquid scintillation technique.
This technique observed the count rate of radon and its
progeny from the eluting the radon from the charcoal isaccomplished by liquid scintillation cocktail and measured
using a liquid scintillation counter40).
In 1987, the United States Environmental Protection
Agency (US EPA) published the protocols for radonmeasurement using charcoal detectors39). In the following
decades, radon measurement systems with charcoal
detectors were applied worldwide due to their advantagesof high sensitivity, low-cost operation, and operation
simplicity. Furthermore, they are often recyclable bydriving off radon and other organic gases after gamma
radiation analysis. In 2019, Pantelic and his team 41)
provided the overview of indoor radon surveys in Europe
and included around 7% of radon measurements were
performed by charcoal detectors. On the other hand, thedisadvantages of this technique are that they require
quick analysis, generally within seven days after the endof exposure periods. Moisture also affects the adsorption
efficiency of activated charcoal. Moreover, the costs ofmeasuring instruments and analysis skills of reading
operators should be considered, because this techniquerequire gamma spectrometers for reading results.
The ACD technique does not require electricity
or special operating skills. After exposure, detectors
can be sent by mail to measure and analyze at otherlocations. However, ACDs cannot be respected as
suitable integrating devices, mainly when the radon
concentration changes rapidly during the measurement
period42). Furthermore, as they allow continual radioactive
decay of radon, their response gives a high weight tothe last day of exposure and is affected by humidity andtemperature43). Therefore, radon measurement with
ACDs is generally used for screening purposes in theindoor environment.
As activated charcoal is an excellent water vapor
absorber, this property reduces absorption capability
for radon. Therefore, humidity correction is required
for this method. Generally, the activated charcoal isheated at over 100 °C for several hours to remove themoisture from charcoal before measuring radon. And

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49

after exposure, the device is tightly sealed and quickly
returned to the laboratory to avoid the effect of humidity
and maintain the maximum sensitivity 44). In someresearch, a diffusion barrier or desiccant, such as silica
gel, has been incorporated in containers to separate theactivated charcoal from the air to reduce the effect ofmoisture45, 46). Sometimes, the ACD is weighted before
and after deployment to evaluate the amount of adsorbed
humidity. Because the change of detector mass due towater adsorption is used to calculate calibration factor
and to select adjustment factor curve for correcting radon
concentration47).
3.3. Electret ion chambers
An electret detector or Electret Ion Chamber (EIC) is
an integrated ionization chamber wherein the electret
functions both as a sensor and a source of the electrostatic
field. Generally, the electret is an electrostatically charged
plastic disc mounted inside a small container made fromconducting plastic, where radon can diffuse througha filter-covered opening of the chamber. The filter
precludes radon progeny into the chamber. EIC provides
the information on a time-integrated radon activity
concentration. The popular commercial version of EIC
is often known under the trade name E-PERM (ElectretPassive Environmental Radon Monitor). It is assumed
that E-PERMs measure radon gas concentrations as low
as 370 Bq m-3 in air with lower 10% error when measured
over 1 day48).
During the exposure period, radon gas can enter
the EIC device, where radon and its progeny undergo
radioactive decay and ionize the air within the chamber.
The positively charged electret collects negative ionsthat have been produced from the ionization of air,resulting in a discharge of the electret, which is related
proportionally to the integrated concentration of radon
inside the chamber. The electric charge on the electretis determined before and after the exposure period byusing a voltage reader (an electret surface potential
voltmeter)49). In general, the electrets should be read andanalyzed as soon as possible after the end of exposure to
avoid continual discharge due to background radiation.
Furthermore, unlike alpha track detectors that are only
sensitive to alpha and particles radiation, electrets arealso sensitive to gamma and other background radiation,
thus necessitating a separate determination of gamma
background radiation. The following equation (Eq. 1)
calculates radon concentration from the EIC device50).
(V i – V f )CRn = ̶̶̶̶ – BG
(T)(CF)(Eq. 1)

C Rn is the actual radon concentration in Bq m-3, V i andV f are the measured initial and final electret voltages,
respectively, T is the exposure time in days, CF is the45

conversion factor in the unit of V per Bq m-3 d and BG
is the radon concentration equivalent of the gamma
background. Note that BG of 0.1 μGy h-1 was measured tobe equivalent to 32 Bq m-3. And a linear correction can bemade to accommodate other BG values.
The EIC can be applied to different exposure periods,
from a few days to a year50, 51), depending on the EIC
design, which is determined by the thickness of theelectret and the volume of the ion chamber. Short-term
devices are designed to expose radon for about twodays to two weeks; thick electret and large volume ion
chamber are used to enhance the high sensitivity ofdevices. Alternatively, thin electret and small volume ion
chambers are used for less sensitive electrets in long-term
EIC devices46), which can provide an average of integrated
radon concentration for the duration of exposure periods
spanning several weeks to a year.
The first advantage of EIC devices is that conducting
measurements do not require many skills, and results
can be obtained in the field, if necessary. Moreover, thedevices are reusable. However, its sensitivity to gamma
radiation can interfere with radon measurement, andhumidity can affect EICs. For example, Sorimachi et al.52)
indicated a slight influence of humidity, ambient
aerosols, and thoron on the responsibility of EICs forradon measurements. Thus, an area with high moistureand extremely high thoron concentrations should be
avoided, and attention must be paid to these factors
when using EICs. Furthermore, EIC is also sensitive toaltitude change, which relates to pressure and air densitychange. At higher altitudes (or at low pressures), fewer
air molecules are available for producing ion pairs in a
traveling path length of radiation compared to the ionsproduced at lower elevations (or at higher pressures).
The corrections of elevation effect should be applied for
obtaining more accurate results whenever EIC is used
for making radon measurements at very high altitudes53),
due to differences in air density that can affect the
distance alpha particles can travel54).
3.4. Thermo-luminescent dosimeters
Thermo-luminescent dosimeters (TLDs) are based onusing crystalline materials in which ionizing radiationtransfers energy to an electron and creates electronhole pairs. When TL materials are irradiated, they store
energy inside their structure, causing electrons andholes to move independently throughout the media.
The amount of energy required to create electron-holepairs is dependent on the energy difference between thevalence band and conduction band of materials. After the
exposure period, the TL materials are generally heated,causes the rapid recombination of electrons and holes,
resulting in the release of light (photons). The intensityof emitted light can be measured using a photomultiplier

46

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49

tube (PMT) in the TLD reader device, and the amountof emitted light is proportional to the radiation dose
accumulated over the exposure period55). For radonmeasurement using the TLD technique, the information
stored in TLDs is not the number of alpha particles but
the total energy of alpha particles. Therefore, the readout
information of TLDs shows directly potential alphaenergy concentration (PAEC), with no dependence on theequilibrium factor.
TLDs were found to function as a radon detector. In
1981, Ho and Weng56) published the newly developed
TLDs technique using TLD (CaSO4: Dy) as a thin foil aspart of a specially designed device for radon measurement
near-surface soil. CaF2: Dy is a type of TLD that Brits andVan57) calibrated to respond to alpha and beta radiationfrom radon progeny. In addition, TLDs are also used tomeasure background gamma radiation together withanother detector type. Additionally, Stranden et al.58)
showed that TLDs could be applied with the charcoal
detector to record the continual gamma emission fromradon progeny captured in charcoal. The average radon
concentration can subsequently be analyzed using a TLD
reader, but this approach is not in general use.
However, TLDs have a limited utilization for radon
dosimetry because most TL materials are sensitive
to whole radiation, including gamma, beta, and alpharadiation. Therefore, one of the problems of radonmeasurement using TLDs is separating the TL signal
associated with alpha particles emitted from radon fromthe signal caused by accompanying beta and gamma
radiation. Generally, this problem can be solved using
at least two TLDs, one sensitive to all ionizing radiation
for determining all radiation emitted from radon and its
progeny, and another to indicate background gamma andbeta radiation59).
4. Recent Advances in Passive Radon Detector
Recently, several research have been conducted in
the field of the development of the passive devices formonitoring and modeling radon and its progeny.
MetroRADON Project, which running in Europe
is one of the radon research projects aim to develop
reliable techniques and methodologies to enable in
the international system of units (SI) traceable radon
activity concentration measurements and calibrations at
low radon concentrations. The calibration methods andmeasurement techniques for some passive devices aredeveloped in the project. As part of this project, compact
discs (CDs) are used for radon measurements, novel
techniques for radon exhalation measurement from soil
based on polymers or track-etching of CDs and liquid
scintillation detector have been developed and evaluated.
It is based on radon absorption in the polycarbonate

material of CDs. Pressyanov and his team60) proposed
the application of CDs method for radon measurements
at workplaces by testing under highly variable exposure
conditions. Good correspondence was observed, small
systematic bias of 3.7% at a depth 80 μm and 13.5% at
a depth 120 μm beneath the front surface of CDs are
explained by the significant variability of the temperatureand radon concentrations during exposure. Furthermore,some topics related to thoron interference in radonby passive detectors are investigated in the project61).
The single-chamber detectors with no discriminative
function are used in some countries to measure radon
concentrations, which may be overestimated due tothoron interference. In order to calibrate and reduce theinfluence of thoron, the influence of thoron on the radon
activity concentration measurements has been observed
and investigated with some radon detectors in thisproject. Related to the case, Sorimachi et al.62) examined
the performance of passive detectors (radon-thoron
discriminative RADUET detector) at exposure to lowlevel radon concentration, and they reported good resultscompared to active radon detectors. The agreements
between the active detectors were within 15%, while
the passive detectors were consistent with those by themonitors within approximately 20%.
Another advanced research project in field of radon
metrology was performed at IFIN-HH, in Romania63).
One of their work objectives which related to passive
devices for radon measurement, is the controlled radon
exposure of several nuclear track detectors placed in
the radon chamber. The TASTRAK solid-state nuclear
track detectors, Polyallyl Diglycol Carbonate (PADC;
CR-39) were used in this work together with the opticalreading system (TASLIMAGE system) as a new highperformance radon dosimetry. Their system showed
good result of the main technical characteristics, such as
fast reading per detector between 40 s and 100 s, lower
detection limit about 10 Bq/m3, upper detection limit
about 10 MBq/m3 and linear response within 5% accuracy
for a radon exposure of 500 kBq·h·m-3.
5. Conclusions
In the present paper, an overview of the passive
measurement techniques of radon and its progeny has
been proposed. The mainstream passive devices formeasuring radon and its progeny are classified into alphatrack detectors, activated charcoal detectors, electretion chambers, and thermo-luminescent dosimeters.
The principles of these devices, their main designs,
influencing factors, the application status of detection
devices, sampling collections, and data analysis have been
described and summarized.
From the comparison of the passive devices: ATDs

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49

and TLDs are suitable for long-term measurement, but
ACDs are potentially for short-term measurement. While
EICs are able to serve for both long-term and short-term
measurement. After the sampling or exposure period,
ATDs, ACDs and TLDs must be sent to a laboratory for
analysis, but EICs are possible to read the results onsite. However, the cost of EIC is high than other devices,
and it require correction for background radiation.
As the same problems of radon measurement using
TLDs is separating the TL signal associated with alphaparticles emitted from radon from the signal caused byaccompanying beta and gamma radiation.
In general, passive devices do not require any power
supply for sampling collections. Therefore, they areusually simple to use, cost-effective, and some of them
are repeatable. For these reasons, passive techniques are
suited for radon measurement in long-term and largescale measurement. However, the efficiency, accuracy,
and stability of the passive radon measurement devices
may be affected by humidity, temperature, thoron activity
concentration, and deposited progenies of radon andthoron. Furthermore, several passive devices detect not
only radon but also thoron and its progeny, resulting
in a possibility for overestimating the level of radon
concentration. This could lead to a biased estimateof the health and lung cancer risk in epidemiologicalstudies. Therefore, there are still many limitations thatmust be subject to an important future developmentof passive-type radon detectors. Although, the future
trend of passive-type radon detectors development canbe changed in many directions, but the demands forcheaper prices, longer lifetime, less maintenance (costeffectiveness), more accuracy and easy to read-out results
are to be expected. And also, consecutive demands
for automatically read-out electronics, interconnection
technologies, data acquisition, and quality assurance.
Author Contributions
Conceptualization, S.T.; Data acquisition and interpretation,
W.P.; Supervision, C.K. and S.T.; Validation, W.P., C.K.
and S.T.; Writing̶original draft, W.P.; Writing̶review
and editing, W.P., C.K. and S.T. All authors have read andagreed to the published version of the manuscript.
Conflict of Interest
The authors declare that they have no conflict of interest.

1995 May;29(5):1359–64.
2.

Appleton JD. Radon: sources, health risks, and hazard mapping.
Vol. 36, Ambio. 2007. p. 85–9.

3.

Cheng ES, Egger S, Hughes S, Weber M, Steinberg J, Rahman B,
et al. Systematic review and meta-analysis of residential radon andlung cancer in never-smokers. Eur Respir Rev. 2021;30(159):1–14.

4.

World Health Organization. WHO Handbook on Indoor Radon: a
Public Health Perspective. World Health Organization; 2009. 110p.

5.

UNSCEAR. Sources and Effects of Ionizing Radiation, United
Nations Scientific Committee on the Effects of Atomic Radiation.
New York, United States: United Nations; 2000.

6.

Hoon Ahn G, Lee J-K. Construction of an environmental radon
monitoring system using CR-39 nuclear track detectors. Nucl Eng
Technol. 2005;37(4):395–400.

7.

Shapiro J, Rajapakshe R. Radiation Protection: A Guide for
Scientists, Regulators, and Physicians, Fourth Edition. Med Phys.
2003;30(4):730–730.

8.

Durrani SA, Ilic R, editors. Radon Measurements by Etched Track
Detectors. Applications in Radiation Protection, Earth Sciences
and the Environment. Singapore: World Scientific; 1997.

9.

IAEA. Analytical Quality in Nuclear Applications Series No.
33: National and Regional Surveys of Radon Concentration in
Dwellings Review of Methodology and Measurement Techniques[Internet]. the IAEA in Austria; 2013. IAEA/AQ/33. [cited 2022
Jun 8]. Available from: https://www-pub.iaea.org/MTCD/
Publications/PDF/IAEA-AQ-33_web.pdf

10.

Fleischer RL, Price PB, Walker RM. Tracks of charged particles
in solids. Science. 1965;149(3682):383–93.

11.

Amgarou K, Font L, Baixeras C. A novel approach for long-term
determination of indoor 222Rn progeny equilibrium factor using
nuclear track detectors. Nucl Instruments Methods Phys Re.
2003;506(1–2):186–98.

12.

Nikezic D, Ng FMF, Yu KN. Theoretical basis for long-term
measurements of equilibrium factors using LR 115 detectors. Appl
Radiat Isot. 2004;61(6):1431–5.

13.

Nikezic D, Yu KN. Long-term determination of airborne
concentrations of unattached and attached radon progeny using
stacked LR 115 detector with multi-step etching. Nucl Instruments
Methods Phys Res. 2010;613(2):245–50.

14.

Ho w a r t h CB, Mi l es JCH, R es u l t s o f t he 20 01 NR P B
intercomparison of passive radon detectors. Great Britain. National
Radiological Protection Board; 2002. Report No.:NRPB-W--21

15.

Nader AF. The determination of equilibrium factor of radon andthoron using LR-115 type II detector in a selected area from Basra
Governorate, Iraq. J Phys Conf Ser. 2019 Oct;1258(1):012032.

16.

Ramola RC, Negi MS, Choubey VM. Measurement of equilibrium
factor “F” between radon and its progeny and thoron and its
progeny in the indoor atmosphere using nuclear track detectors.
Indoor Built Environ. 2016 Jul;12(5):351–5.

17.

Jílek, K., Thomas, J., Tomášek L. First results of measurementof equilibrium factors F and unattached fractions fp of radon
progeny in Czech dwellings. Nukleonika. 2010 Jun;55(4):439–44.

18.

Yu KN, Nikezic D. Long-term determination of airborne radon
progeny concentrations using LR 115 solid-state nuclear track
detectors. Radiat Meas. 2011;46(12):1799–802.

19.

Frank AL, Ogura K, Benton EV. Fading of latent tracks in CR-39
due to environmental conditions. Int J Radiat Appl Instrumentation
Part D Nucl Tracks Radiat Meas. 1986 Jan;12(1–6):83–6.

20.

Bartlett DT. Ageing of and environmental effects on PADC (CR39). Radiat Prot Dosimetry. 1987 Aug;20(1–2):71–5.

21.

Tidjani A. Property modifications in UV irradiated polymeric
track detectors. Nucl Instruments Methods Phys Res. 1991

Reference
1.

Hopke PK, Jensen B, Li C-S, Montassier N, Wasiolek P, Cavallo
AJ, et al. Assessment of the exposure to and dose from radon
decay products in normally occupied homes. Environ Sci Technol.

47

48

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49
May;58(1):43–8.

40.

22.

Moreno V, Font L, Baixeras C, Garcia-Orellana J, Bach J, Grossi
C, et al. Effectiveness analysis of filters used with radon detectors
under extreme environmental conditions for long-term exposures.
Phys Procedia. 2015;80:113–6.

Bem H, Dłługosz-Lisiecka M, Janiak S, Mazurek D, Szajerski
P. Fast determination of indoor radon ( 222Rn) concentration
using liquid scintillation counting. J Radioanal Nucl Chem. 2017
May;312(2):337–42.

41.

23.

Moreno V, Baixeras C, Font L. Experimental study on the effectof high humidity environments on the response of long-term
exposed nuclear track detectors. Radiat Meas. 2013;50:207–11.

Pantelićć G, Čelikovićć I, Živanović M, Vukanac I, Nikolićć JK, CinelliG, et al. Qualitative overview of indoor radon surveys in Europe. J
Environ Radioact. 2019 Aug;204:163–74.

42.

24.

Bochicchio F, Forastiere F, Farchi S, Marocco D, Quarto M,
Sera F. Quality assurance program for LR 115 based radon
concentration measurements in a case-control study: description
and results. Radiat Meas. 2003;36(1–6):205–10.

Gray, D J; Windham ST. NAREL (National Air and Standard
Environmental Laboratory) standard operating procedures forradon-222 measurement using diffusion barrier charcoal canisters.
United States. 1990.

43.

Abo-Elmagd M, Mansy M, Eissa HM, El-Fiki MA. Ma jor
parameters affecting the calculation of equilibrium factor using
SSNTD-measured track densities. Radiat Meas. 2006;41(2):235–40.

George AC. Field Test Experience with Charcoal Canisters for
Measuring 222Radon in Air - RTCA os. In: AARST 2000 International
Radon Symposium. Milwaukee, USA; 2000.

44.

26.

Singh P, Singh P, Singh S, Sahoo BK, Sapra BK, Bajwa BS. A
study of indoor radon, thoron and their progeny measurementin Tosham region Haryana, India. J Radiat Res Appl Sci. 2015
Apr;8(2):226–33.

Canoba AC;, López FO, Oliveira AA, Nuclear R, Authority A.
Radon determination by activated charcoal adsorption andliquid scintillation measurement. J Radioanal Nucl Chem.
1999;240(1):237–41.

45.

27.

Bode Tushe K, Bylyku E, Xhixha G, Dhoqina P, Daci B, Cfarku
F, et al. First step towards the geographical distribution of indoor
radon in dwellings in Albania. Radiat Prot Dosimetry. 2016
Dec;172(4):488–95.

Cohen BL, Nason R. A diffusion barrier charcoal adsorption
collector for measuring Rn concentrations in indoor air. HealthPhys. 1986 Apr;50(4):457–63.

46.

Iimoto T, Tokonami S, Morishita Y, Kosako T. Application ofactivated charcoal radon collectors in high humidity environments.
J Environ Radioact. 2005;78(1):69–76.

47.

Zivanovic M, Pantelic G, Krneta-Nikolic J, Rajacic M, Todorovic
D. Radon measurements with charcoal canisters temperature andhumidity considerations. Nucl Technol Radiat Prot. 2016;31(1):65–
72.

25.

28.

Swedjemark GA. Residential radon Case 4 in the Swedish ICRPproject, SWIP Gun Astri Swedjemark. c2002- [cited 2022 Jun 8].
Available from: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.612.4484&rep=rep1&type=pdf

29.

Friedmann H. Final results of the Austrian radon project. HealthPhys. 2005 Oct;89(4):339–48.

48.

30.

Schmier H, Wicke A. Results from a survey of indoor radon
exposures in the Federal Republic of Germany. Sci Total Environ.
1985 Oct;45(C):307–10.

Kotrappa P, Jesters WA. Electret ion chamber radon monitors
measure dissolved 222Rn in water. Health Phys. 1993 Apr;
64(4):397–405.

49.

31.

Kies A, Biell A, Rowlinson L, Feider M. Radon survey in theGrand-Duchy of Luxembourg̶Indoor measurements related tohouse features, soil, geology, and environment. Environ Int. 1996
Jan;22:805–8.

George AC, Bredhoff N. Current State of The Art in Measuring
Environmental Radon. In: Proceedings of the 2011 International
AARST Symposium, Orlando, Florida.;2011.p. 36–44.

50.

Kotrappa P, Dempsey JC, Ramsey RW, Stieff LR. A practical
E-PERM (electret passive environmental radon monitor) system
for indoor 222Rn measurement. Health Phys. 1990;58(4):461–7.

32.

Sahoo BK, Sapra BK, Kanse SD, Gaware JJ, Mayya YS. A new pinhole discriminated 222Rn/220Rn passive measurement device withsingle entry face. Radiat Meas. 2013 Nov;58:52–60.

51.

33.

Tokonami S, Takahashi H, Kobayashi Y, Zhuo W, Hulber E. Up-todate radon-thoron discriminative detector for a large scale survey.
Rev Sci Instrum. 2005 Nov;76(11):113505.

Kotrappa P, Dempsey JC, Hickey JR, Stieff LR. An electret passive
environmental 222Rn monitor based on ionization measurement.
Health Phys. 1988;54(1):47–56.

52.

34.

Stojanovska Z, Zunic ZS, Bossew P, Bochicchio F, Carpentieri C,
Venoso G, et al. Results from time integrated measurements ofindoor radon, thoron and their decay product concentrations inschools in the Republic of Macedonia. Radiat Prot Dosimetry. 2014
Nov;162(1–2):152–6.

Sorimachi A, Takahashi H, Tokonami S. Influence of thepresence of humidity, ambient aerosols and thoron on thedetection responses of electret radon monitors. Radiat Meas. 2009
Jan;44(1):111–5.

53.

Kotrappa P, Stieff LR. Elevation correction factors for E-PERM
radon monitors. Health Phys. 1992;62(1):82–5.

54.

Vasudevan L, McLain ME. Atmospheric pressure effects on thecalibration constant of alpha-track radon detectors. Health Phys.
1994;66(3):318–26.

35.

Hu J, Yang G, Kranrod C, Iwaoka K, Hosoda M, Tokonami S.
An Improved Passive CR-39-Based Direct 222Rn/220Rn Progeny
Detector. Int J Environ Res Public Heal 2020;17(22):8569.

36.

Rout RP, Mishra R, Prajith R, Jalaluddin S, Sapra BK. Wire meshcapped DRPS based bronchial dosimeter for personal inhalation
dosimetry due to radon progeny. J Radiol Prot. 2021 Jun;41(2):398–
409.

55.

Yamashita T, Nada N, Onishi H, Kitamura S. Calcium sulfate
activated by thulium or dysprosium for thermoluminescence
dosimetry. Health Phys. 1971;21(2):295–300.

56.

Daci B, Tushe-Bode K, Bylyku E, Prifti D. Study of optimal etchingconditions of passive radon detectors (SSNTDʼs Cr-39). AIP Conf
Proc. 2019 Feb;2075(1):160025.

Wei Ho, Pao-Shan Weng. Measurement of radon emanation rate
in soil with thermoluminescent dosimeters. Int J Appl Radiat Isot.
1981 Jul;32(7):521–3.

57.

Cross WG, Tommasino L. Rapid reading technique for nuclear
particle damage tracks in thin foils. Radiat Eff. 1970 Jan;5(1–2):85–
9.

Brits, R.J.N.; Van As D. Methodology for the measurement ofradon with passive instruments. INIS. Radiat Prot Dosimetry.
1984;2:219–21.

58.

David J. Gray STW. EERF Standard Operating Procedures forRadon-222 Measurement Using Charcoal Canisters. United States.
1987.

Stranden E, Kolstad AK, Lind B. The ETB Dosemeter, A passive
integrating radon dosemeter combining activated charcoal and
TLD. Radiat Prot Dosimetry. 1983 Oct;5(4):241–5.

59.

Cosma C, Timar A, Benea V, Pop I, Moldovan M. Carbon

37.

38.

39.

Worawat Poltabtim et al./ Radiation Environment and Medicine 2022 Vol.11, No.2 41–49
molecular sieve for radon and thoron monitoring. Rom J Phys.
2009;54(3):401–5.
60.

Pressyanov D, Poncela LSQ, Georgiev S, Dimitrova I, Mitev K,
Sainz C, et al. Testing and calibration of CDs as radon detectors
at highly variable radon concentrations and temperatures. Int J
Environ Res Public Health. 2019 Sep;16(17).

61.

Pressyanov D, Mitev K, Dimitrova I, Georgiev S, Dutsov Ch,
Michielsen N, et al. Report on the influence of thoron on radon
monitors used in Europe. Sofiiski Universitet Sveti Kliment49

Ohridski (SUBG); 2020 Jun. Report No.: EMPIR 16ENV10 D2.
62.

Sorimachi A, Nagamatsu Y, Omori Y, Ishikawa T. Comparison
experiments for radon and thoron measuring instruments at lowlevel concentrations in one room of a Japanese concrete building.
Appl Radiat Isot. 2021 Jul;173:109696.

63.

Luca A, Rădulescu I, Ioan MR, Fugaru V, Teodorescu C, Barna C,
et al. Recent progress in radon metrology at IFIN-HH, Romania.
Atmosphere. 2022 Feb;13(3):363.