  { $y /0 z 2,**05y,| +2  +* ῌ῍An Application of Mn-impregnated Acrylic Fiber to theDetermination of ,,0Ra and ,,2Ra in Hot Spring Waters
Tomoko NAKANO-OHTA+ and Jun SATO,*(Received Aug. +*, ,**0, accepted Oct. 0, ,**0)+

Department of Nuclear Science and Engineering, Research Reactor Institute, Kyoto University,
Department of Applied Chemistry, School of Science and Technology, Meiji University  ,,0Ra  ,,2Ra +!"#$%&'()*+ , ,-#$./$0

1 2345 6&++ 78 9,
῏

῎


 :;!<=>?@AB ,,0Ra 
Ra CD EFG HICDJK>LABMNOPQRS :TUF
G ,,0 Ra R *.-ῌ2. mBqῌl V+ WX>YZ+,,2 Ra R *.,ῌ+*. mBqῌl V+ WX>Y[G  Ra CD\]R+ NaCl ^ ,,0Ra _R -3 mBqῌlV+ _ ,,2Ra_R // mBqῌlV+ _YZ+ `9a^b_R ,,0Ra R *.0 mBqῌlV+ _ ,,2 Ra _R *.2
mBqῌlV+ _Y[G NaCl ^ Ra cdeCDR`9a^bfZghZHM
 iFG jklmg ,,0 Ra \CDR NaCl ^_R +*. mBqῌlV+ _`9a^_R 3 mBqῌlV+ _YZ+ Mno_b+ NaCl ^ ,,0 Ra CDR`9
a^fZHMpinG  Ra CDR Ca CDq>rstpuo
n+ o> pH #vp Ra CD wxF:BuonG,,2

Abstract
Concentrations of Ra and Ra in hot spring waters from Tokyo area were observed by Mn-impregnated acrylic ﬁber. Applicability of the method to highly saline
waters was examined by use of seawater. The concentrations of ,,0Ra and ,,2Ra in hot
,,0

,,2

* To whom all correspondences should be addressed.

37

$%

38

spring waters ranged from *.- to 2. mBqῌl+ and from *., to +*. mBqῌl+, respectively.
The average concentrations of the hot spring waters were -3 mBqῌl+ for ,,0Ra and //mBqῌl+ for ,,2Ra in NaCl type, and *.0 mBqῌl+ for ,,0Ra and *.2 mBqῌl+ for ,,2Ra in
simple alkaline type, indicating that the concentrations of Ra isotopes in NaCl type weremuch higher than those in simple alkaline type. Average concentration of ,,0Ra of some
hot spring waters in Japan were +*. mBqῌl+ for NaCl type and 3 mBqῌl+ for simple
alkaline type, indicating that the concentration of ,,0Ra in NaCl type was also muchhigher than those in simple alkaline type. Concentrations of Ra isotopes are well correlated with Ca concentrations, and may be controlled by pH of hot spring waters.
Key words : Mn-impregnated acrylic ﬁber, radium-,,0, radium-,,2, hot spring water,
Tokyo area :   ,,0  ,,2 !"#+.

Introduction

As ,,0Ra and ,,2Ra are progenies of ,-2U and ,-,Th, respectively, the concentrations of ,,0Ra
and ,,2Ra are essentially dependent on the U and Th concentration in the source rocks.
Thorium-,-* and ,-,Th, parents of ,,0Ra and ,,2Ra, respectively, are supposed to be insoluble
in hot spring waters with chemical character of neutral and/or alkaline type. The ,,0Ra and
Ra in the hot spring waters are supplied from the relevant rock into water, including,,2chemical leaching from the relevant rock and by the a-recoil ejection from Th isotopes on thesurface of the rock. Assuming that the leaching e$ciency between Ra isotopes from therelevant rock into the hot spring water is equal to each other, the variation in the activity
ratio of Ra isotopes in the hot spring waters may be dependent on the age of hot spring water(Nakano-Ohta and Sato, ,**/) or due to the mixing of waters of di#erent origin in highly
varying proportions. Thus the concentration of ,,0Ra and ,,2Ra is expected to be useful tracer
on the hydrological aspects of natural waters.
Radium isotopes (,,0Ra and ,,2Ra) in hot spring waters have been determined by co-precipitation with BaSO. followed by a-ray spectrometry, g-ray spectrometry or liquid scintillation spectrometry (Ikeda, +3// ; Sugihara, +31* ; Horiuchi and Murakami, +312 ; Horiuchi etal., +313 ; Kanroji et al., +32* ; Kametani and Matsumura, +32- ; Yamamoto et al., +33. ; Chu
and Wang, ,***). However, Ba reagents frequently contain small but signiﬁcant amounts of
Ra of a fraction of + Bq/g. The amount of ,,0Ra impurity in BaCl,ῌ,H,O reagents from -,,0major chemical reagent makers in Japan was observed to be in the range of ,*ῌ+** mBqῌg+(Saito et al., ,**,), which may contaminate with several mBq of ,,0Ra in the co-precipitation
process of sample waters. Though the separation procedure including co-precipitation of
Ra with Ba reagents may be applied to the hot spring water having high concentration of,,0

Ra of +,*** mBqῌl+ or more, it is not preferable for hot spring waters having low con-,,0

centration of ,,0Ra to separate it with BaSO., especially for a minute amount of ,,0Ra of lessthan +* mBqῌl+. Yamamoto et al. (+323) also pointed out that the amount of ,,0Ra impurity
in Ba reagents ranged from +** to .** mBqῌg+ and proposed the procedure to eliminate ,,0Ra
impurity from Ba compounds by cation exchange separation using CyDTA (cyclohexanediaminetetraacetic acid) as eluant. Co-precipitation procedures with BaSO. were reported for,**0/0 ,,0Ra

,,2

Ra 

39

Ra in natural waters, including seawater, of + mBqῌl+, using Ra-free Ba reagent (Yama-,,0moto et al., +33.) or Ba reagent with the known amount of Ra contents. Recently, Saito et al.
(,**,) developed an ion exchange procedure for Ra isotopes in hot spring waters, which wasfree from the contamination of Ra isotopes from reagent.
Moore (+310) reported that Mn-impregnated acrylic ﬁber could collect ,,2Ra from a large
amount of seawater : +** g of the Mn-impregnated acrylic ﬁber could collect up to /** dpm of
Ra in seawater, which was equivalent to +,/** l or more of seawater. Collection of Ra iso-,,2

topes by Mn-impregnated acrylic ﬁber has been applied to various natural waters (Moore,+310 ; Ku et al., +32* ; Yamada and Nozaki, +320 ; Nozaki and Tsunogai, +33* ; Kasemsupaya etal., +33-).
Concentrations of Ra isotopes in hot spring waters were reported to be +0-, mBqῌl+forRa and *.,+,*** mBqῌl+ for ,,2Ra (Sato et al., +31/ ; Horiuchi et al., +313 ; Kanroji et al.,,,0+313 ; Yamamoto et al., +33. ; Saito, ,**/ ; Nakano-Ohta and Sato, ,**0). Though the highly
concentrated Ra isotopes in hot spring waters can be determined with several tens liters ofsample water, Ra of low concentration requires sample volume larger than +** l. This paper
deals with e#ective collection and determination for the concentration of ,,0Ra and ,,2Ra inseawaters and various hot spring waters including highly saline hot spring waters with alarge volume of +** l in Tokyo area.
collection of

Ra and,,0,,2

The present study consists of two procedures : (+)

Ra in seawater and hot spring water of +** l by a column of Mn-

impregnated acrylic ﬁber and (,) determination of ,,0Ra and ,,2Ra by g-ray spectrometry.

,.
,. +

Experiments

Sampling sites and samples
Surface seawater from Tokyo Bay was sampled at Umizuri Park, Kawasaki. Figure +shows sampling sites of hot spring waters and the geology in Tokyo area (Omori, +323). Hot
springs located in Tokyo area are grouped into three localities : (+) metropolitan area, (,)
Tama area and (-) Okutama area (Kanroji et al., ,***). Chemical characteristics of the hotspring waters belong to (+) NaCl and NaHCO- type for metropolitan area, (,) NaCl and NaHCOtype for Tama area, and (-) simple alkaline type for Okutama area. Evaporated residues of hot
spring waters ranged from 32 to /2* mgῌl+ for Okutama area, from +/* to ,,*/- mgῌl+ for
Tama area and from ,,*** to -,,*/* mgῌl+ for metropolitan area (Kanroji et al., ,*** ; Kanroji,,**/, priv. com.), indicating that the evaporated residues in the hot spring waters from themetropolitan area were much higher than those from Okutama area and Tama area.
Hot spring waters and surface seawaters were stored in ,* l polyethylene bottles fortransportation.
,. ,Analytical method
The Mn-impregnated acrylic ﬁber was prepared after the procedure given by Moore(+310). Brieﬂy, +** g of acrylic ﬁber (Hamanaka Co. Ltd.) was put into + l of *.- molῌl+ solution of KMnO. for - h at 1* to form Mn-impregnated acrylic ﬁber, and the product wasrinsed well with deionized water and dried completely in an electric drier oven at /*. The

῎ῑ῏ῐ

40

Fig. +

Sampling sites of hot spring waters in Tokyo area (modiﬁed from Omori (+323).

chemical form of the Mn compound deposited on the acrylic ﬁber and chemical properties ofthe Mn-impregnated acrylic ﬁber are described in detail elsewhere (Ohta et al., ,**.).
The polycarbonate column consists of three sub columns (-./ cm inner diameter, -* cmlong) of -+ g of Mn-impregnated acrylic ﬁber connected in series with each other by putting
plastic net between the columns. Sample waters were passed through the column with a ﬂow
rate of less than , lῌmin῍+. This collection procedure for ,,0Ra in +** l water sample required,./ hours.
This analytical method was applied to seawater, highly saline hot spring water of NaCl
type, NaHCO- type and simple alkaline type. Hot spring waters of 00ῌ+** l were passed
through the column. Two Mn-impregnated acrylic ﬁbers in the ﬁrst and the second columns
were combined to be packed into one air-tight tin canister (10 mm f, ,. mm H). The Mnimpregnated acrylic ﬁbers which collected Ra isotopes were stored for + month for g-ray
spectrometry in order that ,+.Pb and ,,2Ac reached the radioactive equilibrium with ,,0Ra andRa, respectively. Radioactivity of ,+.Pb and ,,2Ac were determined by the -/+ keV and the,,2

3++ keV g-rays, respectively. Detailed discussion on the present spectrometry is described by
Saito et al. (,**,).

 /0  ,**0
Table +



,,0

Ra

,,2

41

Ra

Concentrations of ,,0Ra and ,,2Ra, and ,,2Ra/ ,,0Ra activity ratio in hot spring waters from Tokyo area

Chemical character

Sampling date,,0Ra/
mBqῌl+*

NaCl type
Oyedo-onsen-monogataria
Heiwajima-kurhausa
Kannon-no-yub
Seta-sanga-no-yua
Jindaiji-yukaria
Tennyo-no-yud

Dec 3, ,**/
Dec ,0, ,**.
April -, ,**/
Dec 0, ,**/
July ., ,**/
Aug 2, ,**-

2.,
/2,
.-+
,+*4/+**4,+2+Average
NaHCO- type
Kamataa
HisamatsuaDec ,0, ,**.
July ,, ,**/

Average
Simple alkaline type
Nomekoi-no-yucTsuru-no-yuc
Matsu-no-yuc
Kosuge-no-yuc
Yasuragi-no-satoc

May +., ,**May ,*, ,**May +., ,**July +,, ,**/
May +*, ,**/

Average,,2Ra/
mBqῌl+*Ra/ ,,0Ra

Depth**/
m

+*..
3..
1-+
,-+
+,+
,++

+4,*4++43*4++41*4++4+*4++4,*4++4-*4+

+-**
,***
+/**
+1**
+/**
+0**

-3

//

+4.

+4,*4,*4.3*4*3-4**4.
*41-*4,*,4/*4/+4/*4/

*42/

+43

,4*

*4-**4*2*43.*4,0*400*4*2*4.-*4+**40,*4*0*4,.*4*.
*40-*4*.
+4+*4++*40,*4+/+4,*4,*42*4*41*4,+41*4+4.*4/+43*4,

*40

*42

+4-

,,2

+**
0*

+-**ῌ+/**
-**
-*
+/**
+-**ῌ+/*** Errors represent the counting statistics.
** The depth of bore-hole of hot-spring.
a
Metropolitan areab
Tama areac
Okutama aread
Yamanashi Pref.

-.
-. +

Results and discussion

Surface seawater
Prior to the determination of the Ra isotopes in hot spring water, ,,0Ra in seawater wasdetermined by the Mn-impregnated acrylic ﬁber. Surface seawater (+** l) from Tokyo Bay
sampled at Umizuri Park, Kawasaki, was passed through the column. The Mn-impregnatedacrylic ﬁber recovered from each column was dried to be packed into three canisters separately.
The total amount of ,,0Ra in the initial water sample can be estimated by the calculation
given as follows :C+C*ῌaC,(C*C+)ῌa a+(C,/C+) C*C+/[+(C,/C+)]

ῐΐῑῒ

42
Table , Concentrations of ,,0Ra and ,,2Ra, and ,,2Ra/ ,,0Ra activity ratio in hot
spring waters in Japan (Yamamoto et al.,+33. ; Saito et al., ,**,)
Chemical character
NaCl type
Kagahachiman*ῌ
Nakanomiya*ῌ
Iwama*ῌKeinakyo*ῌ
Tatsuno-kuchi*ῌMisasa +**ῌMisasa ,**ῌOnogawa +**ῌOnogawa ,**ῌArima +**ῌArima ,**ῌHijiori**ῌ
Average
Simple alkaline type
Nakano-yu*ῌ
Akahodani*ῌ
Gero*ῌ
Nozawa*ῌMiyanohara*ῌ
Average

Ra/mBqῌl῍+

Ra/mBqῌl῍+,,2,4*2῎*4,1./4,῎*42/4.2῎*4/,.411῎*4-++,῎.
.2῎+
/,῎3
-/+῎-0-..῎,/,*-῎+.
03῎+*+.῎,-4*3῎*400-14/῎+4++,4-῎+4204++῎*41++1.῎++++,῎/+*+῎+0/,/῎0.
/0/῎.,
0.῎,0
.3῎+.
-,῎-

+4/῎*4*42-῎*4*,,4,῎*4+4-῎*4++40῎*4+,4-῎*4++43῎*4.
+4/῎*4,+40῎*4,*4--῎*4+.
*41+῎*4,,,4,῎*4.

+*.

+.*

+4/

.4/*῎*4..
++4-῎*42,4+-῎*4.+*43/῎*4,.
,/῎+341,῎+40+-41.῎*4-.
.41*῎+4/2,410῎*411,2῎-,4,῎*4-41῎*4,4,῎*40,43῎*4+4+῎*4+

3

+*

,4.

,,0

,,2

Ra/ ,,0Raῌ* Yamamoto et al. (+33.).
**ῌ Saito et al. (,**.).

where C* is the total amount of ,,0Ra in the initial seawater sample, C+ is the amount collectedfrom the initial water sample by Mn-impregnated acrylic ﬁber in the ﬁrst column, C, is theamount collected by the second column from the sample water after passing through the ﬁrst
column, and a is the collecting coe$cient of ,,0Ra for each -+ g of Mn-impregnated acrylic
ﬁber. The third column is the back-up column for the break-through of ,,0Ra from the second
column. The amount of ,,0Ra collected by the third column may be C-῏C*ῌ(+῍a),ῌa.
The amounts of ,,0Ra collected on the Mn-impregnated acrylic ﬁbers were 3- mBq for theﬁrst column and ,. mBq for the second column. The amount of ,,0Ra in the third column wasless than the detection limit. The a is calculated by the amounts of ,,0Ra collected on the
Mn-impregnated acrylic ﬁbers of the ﬁrst and the second column to be *.1-, and the amountof ,,0Ra in the initial seawater sample is estimated to be C*῏+,1 mBq. The amount of ,,0Ra is
calculated to be 0./ mBq for C- and ,.1 mBq in the drain water, suggesting that the amount of
Ra passed through the three columns of the Mn-impregnated acrylic ﬁbers is ,῍ of the total,,0amount of ,,0Ra in +** l of the seawater sample. The ,,0Ra concentration in this seawater
sample was +.- mBqῌl῍+. Seawater (+,1 l) from Tokyo Bay also sampled at Umizuri Park was
passed through the set of the three columns. Two Mn-impregnated acrylic ﬁbers in the ﬁrst

/0  ,**0



,,0

Ra

,,2

Ra

43

Fig. , Correlation between concentrations of ,,0 Ra and ,,2 Ra, and Ca in
hot spring waters from Tokyo area.
 : NaCl type,  : NaHCO- type,  : simple alkaline type.

and the second column were combined and packed into a canister for ,,0Ra analysis with theview of reducing counting duration in case of a large number of samples. The concentrationof ,,0Ra in this seawater sample was +.+ mBqῌl+. Concentration of ,,0Ra in seawater could be
estimated by the amounts of ,,0Ra collected on the combined Mn-impregnated acrylic ﬁber ofthe ﬁrst and second columns, and the volume of sample water. This procedure will result inan underestimation of a few percent of ,,0Ra content, though it is in the order of magnitudeof the counting error for g-ray spectrometry. The presently observed concentrations of ,,0Ra
in surface seawaters from Tokyo Bay are similar to those in previous results (Yamada andNozaki, +320).

ῐΐῑῒ

44

Fig. - Correlation between concentrations of ,,0 Ra and pH of hot springwater from Tokyo area.
῎ : NaCl type, ῏ : NaHCO- type, ῍ : simple alkaline type.

-. ,Hot spring water
Table + lists concentrations of ,,0Ra and ,,2Ra in hot spring waters classiﬁed by chemical

characteristics along with the depth of bore-hole of respective hot spring. The concentrationsof ,,0Ra and ,,2Ra in the hot spring waters ranged from *.- to 2. mBqῌlῌ+ and from *., to +*.
mBqῌlῌ+, respectively. The average concentrations were -3 mBqῌlῌ+ for ,,0Ra and // mBqῌlῌ+ for ,,2Ra in NaCl type, and *.0 mBqῌlῌ+ for ,,0Ra and *.2 mBqῌlῌ+ for ,,2Ra in simple alkaline type, indicating that the concentrations of Ra isotopes in NaCl type were 1* times higher
than those in simple alkaline type.
Table , lists the reported concentrations of ,,0Ra and ,,2Ra in hot spring waters fromJapan classiﬁed by NaCl type and simple alkaline type. The ,,0Ra concentration in hot springwater in Tables + and , ranged from , to -/+ mBqῌlῌ+ for NaCl type and from *.- to ,/ mBqῌlῌ+ for simple alkaline type, and the averaged concentration was 1. mBqῌlῌ+ for NaCl type
and ..2 mBqῌlῌ+ for simple alkaline type, also indicating that the concentrations of ,,0Ra in
NaCl type were much higher than those in simple alkaline type and that the concentrationsof Ra isotopes may be dependent on the chemical characteristics of hot spring water.
Smaller activity ratios of ,,2Ra/,,0Ra in hot spring waters from Nomekoi-no-yu, Tsuru-noyu, Nakanomiya, Arima + and Arima , suggest that these hot spring waters are older than theothers (Nakano-Ohta and Sato, ,**/).
Figure , shows the correlation between the observed concentrations of ,,0Ra and ,,2Ra
and the concentration of Ca for hot spring waters from Tokyo area (Kanroji, ,**/, priv. com.).
The correlation coe$cient (r,) between concentration of ,,0Ra and concentration of Ca is *.20.
The good correlation between concentrations of Ra isotopes and Ca suggests that Ra isotopes
may have been leached chemically from the rocks in the aquifer. Figure - shows the variation

/0

,**0

 ,,0Ra  ,,2Ra 

45

in the concentration of ,,0Ra with pH values. The average pH values are 1.1 for NaCl type and3.3 for simple alkaline type, indicating that the hot spring water with lower pH contains
higher concentration of Ra isotopes, suggesting that the leaching process mentioned above
may be controlled by pH of hot spring waters.

Acknowledgments
The authors are deeply indebted to Dr. Y. Kanroji, Hot Spring Research Center, for his
guidance in the selection of hot springs for the present study. Cooperation of Miss C. Shinagawa, Meiji University, in sampling of hot spring water is gratefully acknowledged.
References
Chu, T.C. and Wang, J. J. (,***) : Radioactive disequilibrium of uranium and thorium nuclide
series in hot spring and river water from Peitou hot spring basin in Taipei. J. Nucl.
Radiochem. Sci., +, /ῌ+*.
Horiuchi, K. and Murakami, Y. (+312) : Study on the simultaneous determination of radium
and radon in the same water sample of mineral springs. Part +Simultaneously determined contents of Ra and Rn in water samples of Misasa, Katsuura, Shirahama, Yugashima, Aziro and Masutomi. J. Balneol. Soc. Jpn., ,3, 02ῌ1/ (in Japanese with English
abstract).
Horiuchi, K., Ishii, T. and Murakami, Y. (+313) : Results on the simultaneous determination ofRn, ,,*Rn and ,,0Ra contents in mineral springs of Izu Peninsula. J. Balneol. Soc. Jpn., -*,,,,2.ῌ23 (in Japanese with English abstract).
Horiuchi, K., Kanroji, Y. and Murakami, Y. (+313) : Geochemical study on the occurrence andsources of Ra and Rn in Shirahama Spa. J. Balneol. Soc. Jpn., ,3, +1/ῌ+2, (in Japanese withEnglish abstract).
Ikeda, N. (+3//) : Chemical studies on the hot spring of Arima III. Investigations on theTenmangu-no-yu Spring, Arima Area. (/). J. Chem. Soc. Jpn., 10, +*13ῌ+*2, (in Japanese).
Kametani, K. and Matsumura, T. (+32-) : Determination of ,-2U, ,-.U, ,,0Ra and ,,2Ra in springwaters of Sanin district. Radioisotopes, -,, +2ῌ,+ (in Japanese with English abstract).
Kanroji, Y., Horiuchi, K., Ishii, T. and Murakami, Y. (+32*) : Ra and Rn concentrations inthermal spring waters from Izu Peninsula. J. Balneol. Soc. Jpn., -+, ,-ῌ-. (in Japanese withEnglish abstract).
Kanroji, Y., Horiuchi, K. and Murakami, Y. (+313) : Geochemical study on the occurrence andsources of Ra and Rn in Katsuura-Yukawa Spa. J. Balneol. Soc. Jpn., ,3, +1/ῌ+2, (in Japanese with English abstract).
Kanroji, Y., Tanaka, S. and Ichiyanagi, H. (,***) : Regional distribution and water qualities of
hot-springs distributed from Tama to Okutama area in Tokyo Metropolis. J. Balneol. Soc.
Jpn., ,1, -,ῌ.0 (in Japanese with English abstract).
Kasemsupaya, V., Tsubota, H. and Nozaki, Y. (+33-) : ,,2Ra and its implications in the Seto
Inland Sea. Esturarine, Coastal and Shelf Science, -0, -+ῌ./.
Ku, T.L., Huh, C.A. and Chin, P.S. (+32*) : Meridional distribution of ,,0Ra in the eastern of

῍ῐ῎῏

46

Paciﬁc along geosecs curise tracks. Earth Planetary Sci. Lett., .3, ,3-ῌ-*2.
Moore, W.S. (+310) : Sampling ,,2Ra in the deep ocean. Deep-Sea Res., ,-, 0.1ῌ0/+.
Nakano-Ohta, T. and Sato, J. (,**/) : ,,2Ra/,,0Ra activity ratio in river water in Okutama area,
western district of Tokyo. Radioisotopes, /., /-+ῌ/.*.
Nakano-Ohta, T. and Sato, J. (,**0) : Determination of ,,0Ra and ,,2Ra in seawater by Mnimpregnated acrylic ﬁber. Radioisotopes, //, ..-ῌ..3.
Nozaki, Y. and Tsunogai, S. (+33*) : The distribution of ,,2Ra and ,,0Ra in the surface waters of
the northern North Paciﬁc. Geochem. J., ,., +ῌ0.
Ohta, T., Saito, T. and Sato, J. (,**.) : Collection of Radium isotopes in natural waters bymanganese-impregnated acrylic ﬁber, Radioisotopes, /-, +ῌ++.
Omori, M., ed. (+323) : Nichiyo-no-chigaku, Tsukiji Shokan, Tokyo (in Japanese).
Saito, T. (,**/) : Estimation of growth rate of Hokutolite from Tamagawa Hot-spring. Proc.
Inst. Natural Sci., Nihon Univ., .*, ,*-ῌ,*1 (in Japanese with English abstract).
Saito, T., Ueda, H., Ohta, T. and Sato, J. (,**,) : Determination of radium isotopes concentrations in hot-spring waters with cation exchange resin. J. Balneol. Soc. Jpn., /,, -ῌ++.
Sato, J., Yokozawa, O. and Saito, N. (+31/) : Radioactive nuclides in the thermal spring waterand its sinter deposits from Sarugajo, Tarumizu city, Kagoshima prefecture. J. Soc. Eng.
Mineral Springs, Jpn., +*, .1ῌ0* (in Japanese with English abstract).
Sugihara, T. (+31*) : On the ,,0Ra and ,,.Ra (ThX) contents of hot spring waters. Memoirs of theFaculty of Liberal Arts & Education. Part II, Mathematics & Natural Sciences, Yamanashi
Univ., ,+, +2,ῌ+23 (in Japanese).
Yamada, M. and Nozaki, Y. (+320) : Radium isotopes in coastal and open ocean surface waterof the western North Paciﬁc. Marine Chem., +3, -13ῌ-23.
Yamamoto, M., Toguchi, A., Sashimono, K., Komura, K., Ueno, K. and Sakanoue, M. (+33.) :,+*Pb and ,+*Po in volcanic products and mineral springs (,)ῌMeasurement of ,+*Pb and,+*Po contents in mineral springsῌ. J. Balneol. Soc. Jpn., .., +2ῌ,1 (in Japanese withEnglish abstract).
Yamamoto, M., Komura, K. and Ueno, K. (+323) : Determination of low-level ,,0Ra in environmental water samples by alpha-ray spectrometry. Radiochim. Acta, .0, +-1ῌ+.,.