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,J. Hot Spring Sci.- /3- ++ῌ,+ ,,**3ῌ῎Comparison of Simpliﬁed Liquid Scintillation Counter(Triathler) with Conventional Liquid Scintillation
Counter in the Measurement of Radon
Concentration in Water
Yumi YASUOKA+, Tetsuo ISHIKAWA,, Nobutoshi FUKUHORI-
and Shinji TOKONAMI,
(Received Sep. ,,, ,**2, Accepted May +,, ,**3)0123456789]¡o¢£¤LMN4OPINQ4RS4TUJK¤78¥ ,Triathler U@YZ
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Abstract
We showed that Triathler can be used for measuring radon concentration of around
1. Bq/kg in water as a direct method. Triathler is cheaper than a conventional liquid+

Kobe Pharmaceutical University, .ῌ+3ῌ+ Motoyamakita-machi, Higashinada-ku, Kobe-shi, Hyogoken 0/2ῌ2//2, Japan. + 
0/2ῌ2//2 .ῌ+3ῌ+.
,
National Institute of Radiological Sciences, .ῌ3ῌ+ Anagawa, Inage-ku, Chiba-shi, Chiba-ken ,0-ῌ2///, Japan. ,   ,0-ῌ2///  !"#$ .ῌ3ῌ+.
-
Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu-shi, Shiga-ken /,*ῌ,+3,, Japan.
-/,*ῌ,+3, %&%&'()*+11  



scintillation counter (LSC), and can be brought to a sampling site. The direct method iseasier than the extraction method required by the Guidelines of Analytical Method ofMineral Springs of Japan (GAMM). The optimized window values of - e$ciency tracing
points were determined at /*ῌ+,*+0 ch, 1/ῌ+,*+0 ch and +**ῌ+,*+0 ch. The counting rate of*ῌ+,*+0 ch was calculated by the three counting rates in the optimized window values
using the least-square method. The counting e$ciency was .1*ῌ. We obtained a set of/ samples (radon concentration : over 0* Bq/kg) for each sampling point and applied ameasuring time of 0* min. Under these conditions, the di#erence between Triathler and
LSC was lower than /ῌ, and the quantiﬁcation limit of Triathler was approximately 1
Bq/kg. This method is available as an alternative of the method required by the GAMM.
Key words : Radon, Water, Liquid scintillation, Triathler, Calibration, Guidelines of Analytical Method of Mineral Springs of Japan+.

Introduction

The liquid scintillation method is commonly used for measuring radon (,,,Rn) concentration in water, and is recommended in the Guidelines of Analytical Method of Mineral Springsof Japan (GAMM) (Ministry of the Environment of Japan, ,**,). According to the GAMM,
a spring with radon concentration of more than 1. Bq/kg is regarded as a mineral spring.
There are many varieties of mineral springs in Japan. The GAMM requires that radon concentration should be measured by either the IM-fontactoscope method or the liquid scintillation method (Ministry of the Environment of Japan, ,**, ; Horiuchi and Murakami, +311 ;Horiuchi, +312). However, the IM-fontactoscope is no longer produced. In addition, we foundthat the radon-in-water concentrations measured with the IM-fontactoscope method deviatedfrom those measured with other methods (Japan Health Physics Society, ,**. ; Ishikawa et al.,,**-, ,**.). Recently, the Hot Spring Law (Onsen-ho, Government of Japan, +32.) was revisedin October ,**1. The revised law requires that the components of mineral springs should bemeasured every +* years. The radon-in-water concentrations will have to be measured using
the liquid scintillation method.
The GAMM adopts the “extraction method” which involves extracting radon from a water sample to toluene scintillator in a bottle, and transferring the scintillator to a vial, thenmeasuring the vial with a conventional liquid scintillation counter (LSC). The toluene scintillator is described in detail in Section ,.+. In this paper, “E-sample” indicates the sample
prepared by the extraction method using a toluene scintillator. The U.S. Environmental Protection Agency (U.S. EPA, +332 ; American Society for Testing and Materials, +333 ; American
Public Health Association, American Water Works Association and Water Environment Federation, +332) adopts the “direct method” which involves adding a water sample to a water
immiscible scintillator in a vial, then extracting radon from the water to the scintillator in thevial and measuring the vial with LSC. For the measurement of radon concentration in mineral spring must be done and meet the GAMM (the radon concentration 1. Bq/kg), Yasuoka
et al. (,**.) proposed that the “direct method” is preferable than the extraction method. Whilethe counting rates of the direct method are reduced by one thirty as compared with theextraction method, the direct method is simpler than the extraction method. In addition, thedirect method makes it easy to prevent radon from escaping from a sample. In this paper,12

& /3 ' ,**3 ! Triathler "#$

“D-sample” and “M-sample” indicate the samples for the direct method using toluene scintillator and high e$ciency mineral oil scintillatorῌ (PerkinElmer Life and Analytical Sciences,
Inc., cat. no. 0NE3/1+), respectively.
The liquid scintillation method has been performed with LSC, which is used in a laboratory only. Recently, a portable and simpliﬁed liquid scintillation counter, Triathler (Hidex
Ltd. in Finland) is commercially available (Haaslahti et al., ,***). It is cheaper than LSC, andcan be brought to a sampling site. If it can be used for the in-situ measurement of radon concentration in water, it will be very useful for the measurement that should be conductedaccording to the GAMM. However, it is not clear how radon concentration in water is measured with Triathler without ,,0Ra standard sources. It is di$cult to use ,,0Ra standard sources
due to Japanese government regulations.
For the measurement of radon concentration in water, the direct method using LSC already has been alternative for the extraction method required by the GAMM (Yasuoka et al.,,**.). The calibration factor of LSC for the direct method was obtained by using a radium
standard (Yasuoka et al., ,**/). The purpose of this study is to demonstrate the direct methodwith Triathler can be used as an alternative of the direct method with LSC. We will describe
how Triathler can be used for the measurement of radon concentration in water by the direct
method. First, a counting rate of a scintillator including high radon concentration is measured with Triathler using the direct method, and it is compared with that measured with LSC
using the direct method to setting desired measuring conditions. Second, the counting ratemeasured with Triathler using the direct method is compared with that measured with LSC
and Triathler for the extraction method. Third, counting rates of scintillator including thevarious values of radon concentration are measured with Triathler and LSC.

,.
,. +

Materials and Methods

Sample preparation
Three kinds of samples (E-sample, D-sample and M-sample) were prepared as follows.

The data are from one representative of ﬁve samples in each group. Much information about
the E-sample (Ministry of the Environment, Japan, ,**, ; Horiuchi and Murakami, +311 ; Horiuchi, +312), the D-sample (Japan Health Physics Society, ,**. ; Yasuoka et al., ,**.) and Msample (U.S. EPA, +332 ; Cook et al., ,**-) has been published concerning the proper method
for sampling water for radon measurement. Groundwater taken from a well in Kobe Pharmaceutical University was used for the experiments. The depth of well, groundwater temperature and pH were 2* m, +2./% and pH 0.2, respectively.
For the E-sample, several tens mL of toluene scintillator was mixed with about + L
groundwater in a bottle by shaking the bottle for , minutes. Radon was transferred into thetoluene scintillator by shaking, i.e., radon was extracted from the groundwater. The scintillator containing radon was transferred to a ﬂask for a uniform radon concentration. Twenty
mL of the scintillator containing radon was transferred into each vial. This method is referred to as the extraction method in this paper. Toluene scintillator contains ,,/-diphenyloxazole (. g/L) and +,.-bis [,-(/-phenyloxazolyl)] benzene (*.+ g/L) in toluene.
13  



The D-sample and M-sample were prepared as follows : groundwater containing radon
was transferred to a ﬂask for a uniform radon concentration. For the D-sample, toluene scintillator (+* mL) was mixed with +* mL groundwater in a vial by shaking the vial for -* seconds. For the M-sample, high e$ciency mineral oil scintillatorῌ (+* mL) was mixed with +*mL groundwater in a vial by shaking the vial for -* seconds (U.S. EPA, +332 ; American Society for Testing and Materials, +333 ; American Public Health Association, American Water
Works Association and Water Environment Federation, +332). Both of them are referred to as
the direct methods in this paper.
The counting rates of the D-sample and the E-sample, which were measured with Triathler, were compared with that measured with LSC to setting desired measuring conditions.
Several tens mL of scintillator (toluene scintillator or high e$ciency mineral oil scintillator)
was mixed with groundwater (about + L) in a bottle by shaking the bottle for , minutes. The
scintillator containing radon was transferred to a ﬂask. To prepare the D-sample, +* mL ofradon-free water and +* mL of the scintillator containing radon were mixed in a vial byshaking the vial for -* seconds. To prepare the E-sample, +* mL of scintillator (radon-free) and+* mL of the scintillator containing radon were mixed in a vial by shaking the vial for -*seconds.
,. ,LSC and Triathler
Triathler has only one photomultiplier tube, while LSC has two photomultiplier tubes

which help di#erentiate background signals from true nuclear decay events in the scintillation vial, using coincidence counting. Also, the shield of Triathler is thinner than that of LSC.
The high background count rate mainly occurs by thermal and electronic background noisein the *ῌ+* keV region (L’Annunziata, ,**-). An optional software of Triathler enables the separation of alpha/beta counting (Haaslahti et al., ,*** ; Horiuchi et al., ,**0). In the present
study, however, we used Triathler without alpha/beta separation software.
,. -Measurement of radon concentration with LSC and Triathler
After waiting for more than . hours, the radon concentrations of samples were measured.

Subscripts of L and T show that the samples were measured with LSC (PerkinElmer Life andAnalytical Sciences, Inc., Tri-Carb ,-**TR) and Triathler (Type .,/ῌ*-.), respectively. For
example, the DL means that D-sample was measured with LSC. The measuring time was +*minutes (unless otherwise stated), except for the DT. The measuring time for the DT was 0*
minutes. Five sets of samples were prepared for each measurement method. The mean andstandard deviation were calculated from the measurements of ﬁve samples.
A background sample for the E-samples was ,* mL of the toluene scintillator. A background sample for the D-samples was +* mL of the toluene scintillator and +* mL of radon-freewater. A background sample for the M-samples was +* mL of high e$ciency mineral oil scintillator and +* mL of radon-free water. All background samples were measured for 0* minuteswith LSC and Triathler. The standard deviations of the background samples were calculated
based on standard error (Eq. +) (Japan Radioisotope Association, ,**+),

14

( /3 ) ,**3

s%

ῌ
῎ ῍


 ! Triathler "#$&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&ῌ

where m is the counting rate of background (cpm), t is the measuring time (min) and s is thestandard deviation of the background.
When the DL and EL-samples were measured with LSC, the optimized window values
have - e$ciency tracing points : /*῎,,*** keV, 1/῎,,*** keV and +**῎,,*** keV. The counting
rate of *῎,,*** keV is calculated by the three counting rates of the optimized window values
using the least-square method (Japan Health Physics Society, ,**. ; Yasuoka et al., ,**. ;Noguchi, +31/a, +31/b). In the case of LSC which we used, the counting e$ciency was provento be .1*ῐ according to our comparison experiments with a ,,0Ra standard (Yasuoka et al.,,**/), while the counting e$ciency is theoretically /**ῐ. In the case of Triathler, the optimized window values of - e$ciency tracing points are discussed in Section -.+.
,. .

Radon concentration
Using the toluene scintillator, the radon concentration (Bq/kg) in water is calculated by

the Noguchi-Saito formula on the gas-liquid distribution described by Saito (Japan Health
Physics Society, ,**. ; Saito and Takata, +33, ; Saito et al., +33- ; Saito and Takata, +33. ; Saito,+331). The equilibrium distribution between toluene scintillator, water, and air was given by
this calculation. Unless otherwise noted, the radon concentration and the counting rates wereindicated considering the decay correction for the elapsed days (between the time of shaking
the sample and the midpoint of counting period for the sample).
PerkinElmer Life and Analytical Sciences, Inc. (,**3, pers. com.) shows radon in water wasmeasured with PerkinElme Tri-Carb LSC in the optimized region from ,** keV to 0** keV,using the ML-sample. For this sample, +* mL high e$ciency mineral oil scintillator was mixed
with +* mL groundwater in a vial by shaking the vial for -* seconds. In addition, PerkinElmer
Life and Analytical Sciences, Inc. suggested that the radon concentration (Bq/L) in the
groundwater would be calculated using Eq. (,) following the standard method 1/**-Rn (American Public Health Association, American Water Works Association and Water Environment
Federation, +332).
*.03-'T῎+
CR%netcps'expῌ'&&&&&&&&&&&&&&&&&&&&῍
῍ -.2,. ῏ -.,'*.*+
where netcps (cps) is the net count per second (i.e., after subtraction of background), T is thelength of elapsed days, -.2,. is the half life of radon in days, the groundwater volume is *.*+
L, the calibration constant is -., cps/Bq and CR is radon concentration (Bq/L) in the groundwater.
,. /Measuring various radon concentration in water
According to Ministry of the Environment of Japan (,**,), the spring water with a radon

concentration of more than 1. Bq/kg is regarded as “mineral spring”, one of the varieties ofmineral springs. The net counting rates (within a range of *῎,,*** keV) corresponding to aradon concentration of about 1. Bq/kg are about /,3** cpm (E-sample) and +3* cpm (D-sample).
The E-sample and D-sample were allowed to stand for some days and then measured again
15  

the samples of varied radon concentration were measured with LSC and Triathler. For asingle sample, the counting rate measured with LSC was compared with the counting ratemeasured with Triathler. The radon concentration and the counting rates were calculated
considering the decay correction for the elapsed days (between the midpoint of counting
period for the sample measured with LSC and that measured with Triathler).
Using the / levels of radon concentration in water (from 0* Bq/kg to +-* Bq/kg), the radon
concentration was measured with the direct method (U.S. EPA, +332 ; Cook et al., ,**- ; Japan
Health Physics Society, ,**. ; Yasuoka et al., ,**.) and the extraction method (Ministry of theEnvironment of Japan, ,**, ; Horiuchi and Murakami, +311 ; Horiuchi, +312). D-sample wasmeasured with LSC (DL) and Triathler (DT), ML-sample was measured with LSC, and E-sample
was measured with LSC (EL) and Triathler (ET).
While Triathler is a portable device and can be brought to a sampling site, the LSC can
not be moved from a laboratory. For this reason, the samples sometimes need to be sent toa laboratory by refrigerated (/) cargo. In this case, we investigated how long the samples
were stored at room temperature before starting the measurements. DL- and ML-samples wereprepared by the groundwater, and the samples set aside in the dark for . hours. At starting
time, the counting rates of the DL- and ML-samples were about /,/** cpm and .,*** cpm, respectively. These samples were refrigerated (/) for +2 hours, and were repeatedly measured
with LSC for -* hours.

-.
-. +

Results and Discussion

Determining optimized window values of Triathler
The samples were measured with Triathler by setting -,P key. Figure + shows the pulse

height spectra of radon and its decay products of DT-sample measured with Triathler. The
optimized window values of - e$ciency tracing points were determined at /*ῌ+,*+0 ch, 1/ῌ+,*+0 ch and +**ῌ+,*+0 ch. The - e$ciency
tracing points are available due to exception of the *ῌ+* keV region, in which thehigh background count rate mainly occurs.
The starting channels (/*, 1/ and +** ch)could be determined in the beta area ofFig. + (see Appendix I). There were noise
counts over +,*+0 ch. The counting rate of*ῌ+,*+0 keV is calculated by the three counting rates in the optimized window values
using the least-square method. Under these
conditions the samples were measured with
Triathler. Table + shows D and E-samples
were measured with LSC (DL and EL) and
Triathler (DT and ET). There were no signiﬁcant di#erences (the signiﬁcance prob16

Fig. + Pulse height spectrum of radon and its decay
products measured DT-sample and backgroundsample with Triathler. The optimized window valuesof - e$ciency tracing points were determined /*ῌ
+,*+0 ch, 1/ῌ+,*+0 ch and +**ῌ+,*+0 ch.
DT : The direct method performed with Triathler using toluene scintillator.

) /3 * ,**3  #$% Triathler "&'(!"

ability (P values) ranged from *.0 to *.3) between EL and others (ET, DL, and DT). If the net
counting rate of *ῌ,,*** keV (LSC) is over 1,*** cpm, the results between the DL-sample andthe others (DT, EL and ET-samples) were same. In the case of Triathler, the counting e$ciency
was estimated to be .1*ῌ.
-. ,Measuring various radon concentration in water
For a single sample, the counting rate measured with LSC was compared with the count-ing rate measured with Triathler. Figure ,a shows the relationship between the EL net counting rates of *ῌ,,*** keV and the ET net counting rates of *ῌ+,*+0 ch when the E-sample wasmeasured. Figure ,b shows the relationship between the DL net counting rates of *ῌ,,*** keVand the DT net counting rates when the D-sample was measured. If a single sample is measured with some LSCs, the acceptance limits of di#erences are/ῌ (U.S. EPA, +332). DL (or EL)
was deﬁned as a standard. Hereafter the di#erence (Di#erence ῌ) between DL (or EL) and DT(or ML or ET) means the following Eq. (-) :Table + Results of measuring E-sample and D-sample with conventional liquid scintillation
counter (LSC) and Triathler

Background
Averagestandard deviation
Signiﬁcance probability DL
Signiﬁcance probability EL

DL

DT

EL

ET

+2
15/20..

+.+
15/3,.0,*421,1
15.10,+2
*40-





,/2
15.2.+1/
*40.
*423

DL : The direct method performed with LSC using toluene scintillator.
DT : The direct method performed with Triathler using toluene scintillator.
EL : The extraction method performed with LSC using toluene scintillator.
ET : The e extraction method performed with Triathler using toluene scintillator.

Fig. , The integral counting rate of conventional liquid scintillation counter (LSC) versus Triathler.
a) Extraction method : the di#erences of the counting rate of Triathler were less than /ῌ.
b) Direction method : the di#erences of the counting rate of Triathler were less than /ῌ.
 : the di#erences of the counting rate of Triathler were more than /ῌ

17   Difference ῍



DTDL
+** ῌ
DLThe di#erences between EL and ET were within/῍. However the some di#erences between
DL and DT were over/῍. As a result, the method, which E-sample is measured with Triathler instead of LSC, is fully capable of measuring the criteria of mineral spring (more than
1. Bq/kg).
D-sample was measured with LSC and Triathler, and ML-sample was measured with LSC,
using the / levels of radon concentration in water (from 0* Bq/kg to +-* Bq/kg). Table ,shows radon concentrations, the di#erences in the radon concentration between DL-samples
and others (DT-sample, ML-samples, EL-sample and ET-sample), and the measuring times. In
our experiment, the di#erences between DL-sample and others (DT-sample, EL-sample andET-sample) were within0῍ (ῌ,./῍, ῌ/.1῍ and ῌ..3῍, respectively). Additionally,

Table ,
MethodLiquid Scintillator

Result of the measurement.

Direct method
Toluene scintillator

Extraction method
High e$ciency
mineral oil

Toluene scintillator

Equipment

LSC

Triathler

LSC

LSC

Triathler

Backgroundcounting rate (cpm)

+2

+.+

/4/

,1

,/2

DL (Bq/kg)
Standard
M.T.

DT (Bq/kg)
Di#erence ῍M.T.

ML (Bq/L)
Di#erence ῍M.T.

EL (Bq/kg)
Di#erence ῍
M.T.

ET (Bq/kg)
Di#erence ῍
M.T.

/24-+41
-* min/34*+4++41῍
0* min0,42*43
14-῍-* min0*4**40,42῍+* min0*4/*43-41῍+* min0040+43-* min0/4/-4*
+41῍
0* min1+41,414*῍-* min1*4.+4,/41῍+* min0343+4.43῍+* min1.4/+4+-* min1-41*4,
+4+῍
0* min2*4+*414/῍-* min104-*41,4.῍+* min1.42*4.
*4-῍+* min++24,-4.
+* min++042+4+4,῍
0* min+,-40,42/4/῍+* min++34/+43+4+῍+* min++24.,4/*4,῍+* min+,143,42+* min+,.41,4,,4/῍
0* min+,240-41*4/῍+* min+,/43+4/
+4/῍+* min+,-42+4,
-4,῍+* minRadon concentration

DL : Direct method performed with LSC using toluene scintillator.
DT : Direct method performed with Triathler using toluene scintillator.
ML : Direct method performed with LSC using high e$ciency mineral oil
M.T. : Measuring time
LSC : Conventional liquid scintillation counter18

* /3 + ,**3 ! Triathler "#$

the di#erences between DL-sample and ML-sample were also within%1./ῌ.
The quantiﬁcation limit of the counting rate (Q cpm) is deﬁned in terms of equation (.),
Q&+*s '''''''''''''''''''''''''''''''''''ῌ
where s is the standard deviation of the background. The background for DT (+.1 cpm) wasmuch higher than the background for DL (+2 cpm) and ML (..0 cpm). If the measuring times ofDT, DL, and ML were 0* min., +* min., and +* min., the quantiﬁcation limits of radon concentrations for DT, DL, and ML-samples were approximately 1 Bq/kg, / Bq/kg and . Bq/L, respectively.
After the samples were refrigerated (/() for more than 0 hours, the radon concentrationsof ML-samples showed the level at starting time, and the radon concentrations of DL-samples
ranged from 3/ to 32ῌ of the level at starting time.

..

Conclusions

We showed that Triathler with the extraction method can be used for measuring waterwith a radon concentration of around 1. Bq/kg, which is the criterion of “mineral spring”. We
also showed that Triathler with the direct method can be used for measuring of radon concentration in groundwater. The optimized window values of - e$ciency tracing points were
determined at /*῍+,*+0 ch, 1/῍+,*+0 ch and +**῍+,*+0 ch. The counting rate of *῍+,*+0 keV iscalculated by the three counting rates in the optimized window values using the least-square
method. The counting e$ciency was estimated to be .1*ῌ. If we obtain a set of / samples(radon concentration : over 0* Bq/kg) for each sampling point and apply a measuring timeof 0* min., the di#erences between Triathler and LSC were lower than /ῌ (),./ῌ in our experiment), and the quantiﬁcation limit was approximately 1 Bq/kg. This method is available
as an alternative of the GAMM.

Acknowledgments
We gratefully acknowledge the editor and two anonymous reviewers whose valuable andhelpful comments improved our manuscript.
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19  



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& /3 ' ,**3 ! Triathler "#$

Saito, M., Takata, S. and Masuda, Y. (+33-) : Improved calculation for measurement of ,,,Rn inwater. Radioisotopes, .,, --*ῌ--..
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gov/ogwdw/standard/v&e-frn.pdf, Accessed +2 March ,**3.
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(,**.) : Determination of radon concentration in water using liquid scintillation counter.
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Appendix I
Figure A+ shows the pulse height spectra of radon and its decay products for
DT-sample measured with two Triathlers(Type .,/ῌ*-.). There were individual differences in the spectrum. In this paper, weused Triathler with the spectrum I. The
optimized window values of - e$ciency
tracing points from both of Triathlers were
determined at /*ῌ+,*+0 ch, 1/ῌ+,*+0 ch and+**ῌ+,*+0 ch. The counting rate of *ῌ+,*+0
keV is calculated by the three counting
rates in the optimized window values using the least-square method. The counting rates of EL-sample (about +-,*** cpm)

Fig. A+ The pulse height spectra I and II of radon andits decay products for DT-sample. The spectra were
measured with two Triathlers (year purchased : ,**/
(spectrum I) and ,**1 (spectrum II)), whose models
were same (Type .,/ῌ*-.). In this paper, we used
Triathler with the spectrum I.

were higher than the counting rates of ETsample (spectrum I : +.0%*.3ῌ, spectrum II ,.+%*.2ῌ). If a single sample is measured some
LSCs, the acceptance limit of error is%/ῌ (U.S. EPA, +332). The di#erences between ETsample and EL-sample were within%/ῌ. The counting rates of DL-sample (about 1,*** cpm)
were higher than the counting rates of DT-sample (spectrum I : +.0%+.-ῌ, spectrum II ,.2%+..ῌ). The variation of the pulse height spectrum has the possible e#ect on the counting rate.

21