Radiation Protection Dosimetry Advance Access published May 8, 2015 Radiation Protection Dosimetry (2015), pp. 1–5
doi:10.1093/rpd/ncv263
A HIGH NATURAL RADIATION AREA IN KHAO-THAN HOT SPRING, SOUTHERN THAILAND T. Bhongsuwan* and S. A. Auisui Department of Physics and Geophysics Research Center, Faculty of Science, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand *Corresponding author: [email protected]
INTRODUCTION For many years, radioactivity in hot spring has been recognised and evidenced. The high background radiation areas around the world such as India, Japan, Iran and China have been studied to estimate the risk and effect of long-term low-level exposures to the public(1 – 6). Hot spring water, originated at depths in the earth’s crust, came towards large surface of a specific geologic unit, like granite, which contained some natural radionuclides, for example, radium and thorium(5, 7). The concentrations of 226 Ra and 222Rn in hot spring samples therefore depended on the hydrogeological features of the aquifer and distribution of the parent element in the rock matrix(5). The solubility of radionuclides could affect fluid characteristics (chemical and physical) of the aquifer(5). Rock can be disintegrated or altered by chemical weathering via hydrolysis, oxidation and carbonation(8 – 10). It could occur intensely at a high temperature where heat was originated at depths and transported through water to the earth surface in the fault and fracture zones. Consequently, the concentration of radionuclides in hot spring area depends on the type and abundance of radioactive minerals found in the surrounding rock(10), which indicates the source rock of radionuclides presented in the area. The study area of Khao-Than hot spring is located in the Tha-Chang District, Surat Thani Province, Southern Thailand. It is one of the archaeological, ancient and hot spring natural park sites in Thailand(11, 12). Approximately 738 local people live in the villages nearby the hot spring, with an area of around 47 km2. The number of tourists visiting the hot spring varies
between 5 and 10 persons per day but many more on weekends and holidays(13). The objectives of this study are (i) to determine the natural radioactivity level and analyse for the mineral characteristics in samples in the Khao-Than Hot Spring, (ii) to estimate the radiological characteristics of the sample materials and (iii) to identify the source rock of radionuclides in the area. MATERIALS AND METHOD Geology setting The general geology of the area is predominantly composed of Permo-Carboniferous (CP) and Triassic– Jurassic (TrJ) siliciclastic sedimentary rocks and Jurassic granite (Jgr) (Figure 1). Permian limestone (Pr) hills are located north of and underneath the study area. The Khlong Marui Fault is a major active fault zone in the area lineated predominantly in NNE–SSW directions (Figure 1), where the silicified rocks and carbonate soils were found locally in this zone(11, 12). Sampling and sample preparation Gamma dose survey performed at 1 m above the ground surface in this hot spring area showed that the dose rate ranged from 0.02 to 50 mSv h21, which was used to select the sampling localities (Figure 1). The location of the sampling sites was made using a handheld GPS (GARMIN etrex, USA). The recently deposited soil samples, rock samples and hot spring mud samples of ca. 2 kg each were manually collected from an area of ca. 16 000 m2 in natural and concrete ponds. Sampling interval was separated by a distance of ca. 1 – 10 m apart. The samples were
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
Natural radioactivity in Khao-Than hot spring area, Surat Thani Province, Thailand was investigated. Gamma dose survey indicated a possible high radiation risk for this area. Rock, soil and hot spring mud samples were collected and analysed by a low background gamma spectrometer. The activity concentrations of 226Ra, 232Th and 40K in samples were 151– 139 092 (mean 5 13 794), 12– 596 (127), 24– 616 (215) Bq kg21, respectively. X-ray diffraction and Fourier transform infrared spectroscopy indicated that quartz and calcite (CaCO3) are the main constituents in mud samples with varying contents. In conclusion, this study area was reasonably classified as a high natural background radiation area. The source of radium in this area is supposed to be related to the fault fluids enriched in radium that precipitated with calcium in the carbonate terrain and partly absorbed by high cation exchange capacity clays.
T. BHONGSUWAN AND S. A. AUISUI
kept in plastic bags before transporting them to the laboratory where the samples were crushed into fine powder and then sieved to ,2 mm particle size. The samples were dried in an oven at 1108C for 24 h, then weighed about 200 g each, packed and sealed in an airtight polyvinyl chloride container to prevent the escape of radon(15). The samples were kept sealed hermetically about 4 week to allow radioactive secular equilibrium among the 226Ra, 232Th and their decay products. Mineralogy study (i)
(ii)
X-ray diffraction (XRD): XRD pattern of powdered samples was examined at room temperature by XRD (Phillips X’Pert MPD), Cu-Ka1 radiation (l ¼ 1.5406 A8) tube at 40 kV and current of 30 mA, with the diffraction pattern analysing from 58 to 908 (2u) at a step of 0.028. Mineralogy was identified using the computer program X’-pert High Score Plus(7, 16). Fourier transform infrared spectroscopy (FTIR): The samples for FTIR analysis were dried in an oven at 1008C to remove the moisture. The KBr
pellet technique was used to prepare the samples with the KBr:sample ratio of 100:1. The infrared spectra of sample were measured by an Equinox 55, Bruker spectrophotometer in transmission mode, in the region of 4000–30 cm21, with 2 cm21 resolution(16). Radionuclides measurements The activity concentration of radionuclides 226Ra, 232 Th and 40K in samples was measured using a HPGe coaxial detector (Canberra, Model GC 1319, USA) with an active volume of 59.9 cm3, 1.75 keV full width at half maximum at 1.33 MeV gamma energy. The detector was surrounded by a low background lead shield (Canberra Model 747, USA). The data acquisition and analysis were carried out using a Genie2000 software package (Canberra, USA)(15). The 226Ra, 232Th and 40K were analysed from gamma ray peaks at several energies. Gamma rays from 214Pb (at 295.2 and 351.9 keV) and 214Bi (at 609.3, 1120.3 and 1764.3 keV) were used to determine the 226Ra activity. Gamma rays emitted from 228Ac
Page 2 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
Figure 1. Simplified map of Khao-Than Hot Spring of Surat Thani Province, Southern Thailand with sampling locations. Broken lines indicate traces of Khlong Marui Fault zone(11, 14). CP, Pr, Jgr, TrJ and Q denote Permo-Carboniferous siliciclastic rock, Permian limestone, Jurassic granite, Triassic–Jurassic siliciclastic rock and Quaternary sediment, respectively. Samples named rk3, so45 and so67 are outside the map.
HIGH RADIATION AREA IN KHAO-THAN HOT SPRING
(338.3, 911.6 and 969.1 keV) were used for 232Th, whereas 40K was determined from 1460 keV gamma energy(15). The IAEA CU-2010-03 WWOPT soil sample containing known contents of radionuclides was used for efficiency calibration of the system. The counting time was set to 10 800 s.
RESULTS AND DISCUSSION Mineralogy XRD analysis
FTIR analysis
Figure 2. The XRD patterns of samples m15 and m32 with identified minerals K, kaolinite; C, calcite; Q, quartz and H, halite.
The FTIR spectra of representative samples having varying 226Ra contents are shown in Figure 3. The minerals identified from FTIR include quartz (Q) and calcite (C, CaCO3) with varying contents that are observed from the IR absorption band at 1796– 1807
Figure 3. FTIR spectra of representative samples (sites m15, m21, m24, m30 and m32) and standard minerals, quartz, CaCO3 and kaolinite. Mineral abbreviations include C, CaCO3; Q, quartz; K, kaolinite; M, montmorillonite and O.C., organic carbon(16).
Page 3 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
The XRD spectra of the two representative mud samples from selected sites (sites m15 and m32) are shown in Figure 2. Mud sample m15 contains the highest radium content, while sample m32 has the lowest. XRD spectra indicate that calcite (CaCO3) is the major mineral in sample m15, the highest radium content, whereas quartz (Q), halite (H) and kaolinite (K) are present in sample m32. These minerals are consistent with the geological environment of the study area. Quartz and kaolinite represent the weathering products of Jurassic granite (Jgr) located nearby (Figure 1), whereas calcite (CaCO3) and halite (NaCl) represent dissolution/precipitation of Permian limestone (Pr) and saline intrusion, respectively.
T. BHONGSUWAN AND S. A. AUISUI Table 1. Activity concentrations of 226Ra, 232Th and 40K with their uncertainties in all samples(15). No. Name
m5 m14 m15 m16 m17 m18 m19 m20 m21 m22 m23 m24 m25 m26 m27 m28 m29 m30 m31 m32 m33 rk2 rk3 so8 so9 so10 so44 so45 so67 max min mean
232 Th (Bq kg21)
40 K (Bq kg21)
H
9561+45 4441+31 139 092+188 63 535+127 6841+40 2015+21 2028+23 5375+35 7016+31 3043+28 2307+26 31 439+72 10 538+38 1758+18 2036+19 5227+27 11 713+50 50 221+109 15 873+60 372+8 1150+16 469+15 657+9 1065+27 3139+47 5194+58 10 201+99 151+10 3583+31 139 092+188 151+10 13 794+45
35+9 350+18 596+68 257+34 64+12 48+7 41+6 159+14 99+10 64+9 58+7 243+24 71+12 128+8 22+4 31+5 55+8 124+26 59+11 29+4 140+9 52+15 12+2 45+15 71+31 127+34 408+91 145+13 144+13 596+68 12+2 127+18
233+35 95+16 207+99 150+86 97+22 152+15 191+18 76+17 116+22 306+24 209+22 179+40 281+27 257+19 297+20 283+20 256+33 240+61 252+36 156+12 616+29 24+21 153+11 71+40 40+16 48+87 546+137 571+45 130+18 615+29 24+21 215+36
26 13 38 17 19 6 6 15 19 9 7 86 29 5 6 14 32 13 43 1 4 1 2 3 9 15 29 1 10 38 1 38
Radionuclide concentrations The distribution of the radionuclides 226Ra, 232Th and 40K in all samples is presented in Table 1. Jeasai et al.(17) reported the average concentration of 226Ra in hot spring water from Khao-Than at 2640 mBq l21. The average activity concentrations rank for all samples follows 226Ra . 40K . 232Th as shown in Figure 4. Over 86 % of the analysed samples contain 226 Ra concentrations of .1 kBq kg21. During the course of dose survey using a survey meter at 1 m above ground in this area, the maximum dose rate was found at 50 mSv h21, which corresponded to an effective dose of 438 mSv for a year of exposure. Distribution of 226Ra in all mud samples shows the lowest one in concrete pond (m32; 372 Bq kg21) and the highest in natural pond (m15; 139 092 Bq kg21). The minerals such as montmorillonite, kaolinite and quartz found in mud samples are the result of chemical weathering of Jurassic granite (Jgr) exposed nearby, whereas CaCO3 is originated from dissolution/ precipitation of Permain limestone (Pr) basement underneath the hot spring area. NaCl present in
Figure 4. The relative concentration of 226Ra, 232Th and 40K of the measured samples in the study hot spring.
Page 4 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
226 Ra (Bq kg21)
cm21. Other minerals, kaolinite (K), montmorillonite (M) and organic carbon (O.C.), are also identified from different wave numbers as suggested(7, 16). It can be seen in Figure 3 that radium content in mud samples roughly related to IR absorption intensity of CaCO3 in FTIR spectra. However, the content of high cation exchange capacity (CEC) clays, montmorillonite (M) and the organic carbon (O.C.) in measured samples may play an important role to the total amount of radium in them.
HIGH RADIATION AREA IN KHAO-THAN HOT SPRING
CONCLUSION The results reveal abnormally high concentrations of Ra in mud samples collected from Khao-Than hot spring area. 226Ra is supposed to present in fault fluid in the Khlong Marui Fault that cut across the Jurassic granite nearby and pass underneath this hot spring area. Decomposed granite in the Khlong Marui Fault zone is the most probable source rock of radium in the hot spring area. The XRD and FTIR analyses indicate that quartz and calcite are the major mineral constituents in mud samples together with high CEC montmorillonite and other clays. 226
FUNDING The Department of Physics and Geophysics Research Center, Faculty of Science and the Graduate School, Prince of Songkla University are acknowledged for grant and necessary facilities supports. REFERENCES 1. Onishchenko, A., Zhukovsky, M., Veselinovic, N. and Zunic, Z. S. Radium-226 concentration in spring water sampled in high radon regions. Appl. Radiat. Isot. 68, 825 –827 (2010). 2. Marovic, G., Sencar, J., Franic, Z. and Lokobauer, N. Radium-226 in thermal and mineral springs of Croatia and associated health risks. J. Environ. Radioact. 33, 309 –317 (1996).
3. Beitollahi, M., Ghiassi-Nejad, M., Esmaeli, A. and Dunker, R. Radiological studies in the hot spring region of Mahallat, central Iran. Radiat. Prot. Dosim. 123(4), 505–508 (2007). 4. Bolca, M., Sac, M. M., Altinbas, U. and Camgoz, B. Chemical and radioactivity effects of geothermal springs on environmental pollution in Seferihisar region in western Turkey. Asian J. Chem. 19(3), 2265–2276 (2007). 5. Roba, C. A., Nita, D., Cosma, C., Codreab, V. and Olah, S. Correlations between radium and radon occurrence and hydrogeochemical features for various geothermal aquifers in Northwestern Romania. Geothermics 42, 32– 46 (2012). 6. Dragovic, S. D., Jankovic-Mandic, Lj. J., Dragovic, R. M., Dordevic, M. M. and Dokic, M. M. Spatial distribution of the 226Ra activity concentrations in well and spring waters in Serbia and their relation to geological formations. J. Geochem. Explor. 12, 206–211 (2012). 7. Tabar, E., Kumru, M. N., Sac, M. M., Ichedef, M., Bolca, M. and Ozen, F. Radiological and chemical monitoring of Dikili geothermal waters western Turkey. Radiat. Phys. Chem. 91, 89–97 (2013). 8. Maes, A., Stul, M. S. and Cremers, A. Layer chargecation-exchange capacity relationships in montmorillonite. Clays Clay Miner. 27(5), 387–392 (1979). 9. Uddin, F. Clays, nanoclays, and montmorillonite minerals. Miner. Met. Mater. Soc. ASM Int. 39A, 2804–2814 (2008). 10. Vaculikova, L. and Plevova, E. Identification of clay minerals and micas in sedimentary rocks. Acta Geodyn. Geomater. 2(138), 167–175 (2005). 11. Bhongsuwan, T., Durrast, H., Yordkayhun, S., Nuannin, P. et al. Integrated Geophysical Studies of the Fault Zones in Southern Thailand. Geophysics Research Center, Prince of Songkla University (2013). 12. Chaturongkawanich, S. Geothermal Resources of Changwat Suratthani. Department of Mineral Resources, Thailand (2001). 13. Personnel communication: Khao-Than Sub-District Administrative Organization (2014). 14. Khlong Marui Fault, Active fault map in Thailand, Department of Mineral Resources (2012). 15. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and Effects of Ionizing Radiation: UNSCEAR 2008 Vol. 1. United Nations (2010). 16. Suresh, G., Ramasamy, V., Meenakshisundaram, V., Venkatachalapathy, R. and Ponnusamy, V. A relationship between the natural radioactivity and mineralogical composition of the Ponnaiyar river sediments. India J. Environ. Radioact. 102, 370– 377 (2011). 17. Jeasai, S., Bhongsuwan, T. and Chittrakarn, T. Specific activity of Ra-226 in water from hot springs and nearby shallow wells in Suratthani Province. Kasetsart J. 11(4), 45– 54 (2011).
Page 5 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
mud samples clearly indicates a result of saline intrusion to the groundwater in the study area that is very close to the sea. Montmorillonite is present in the high-radiumactivity samples (m15, m21, m24 and m30), but it is not present in the lowest radium containing sample (m32). A high CEC of montmorillonite is probably a major cause of absorbed radium in these samples. CaCO3 can be dissolved or precipitated in water, depending on several factors. Consequently, the 226Ra is precipitated together with calcium, forming calcium/radium carbonates in the presence of hot spring. Evidences in the field survey indicated a very high dose in an area where porous carbonates (CaCO3 or limestone) were spreading over the top soil. The texture of this porous CaCO3 indicated precipitation of carbonates from hot spring water. This complex chemical environment represents the characteristics of the study area.
doi:10.1093/rpd/ncv263
A HIGH NATURAL RADIATION AREA IN KHAO-THAN HOT SPRING, SOUTHERN THAILAND T. Bhongsuwan* and S. A. Auisui Department of Physics and Geophysics Research Center, Faculty of Science, Prince of Songkla University, Hatyai, Songkhla 90112, Thailand *Corresponding author: [email protected]
INTRODUCTION For many years, radioactivity in hot spring has been recognised and evidenced. The high background radiation areas around the world such as India, Japan, Iran and China have been studied to estimate the risk and effect of long-term low-level exposures to the public(1 – 6). Hot spring water, originated at depths in the earth’s crust, came towards large surface of a specific geologic unit, like granite, which contained some natural radionuclides, for example, radium and thorium(5, 7). The concentrations of 226 Ra and 222Rn in hot spring samples therefore depended on the hydrogeological features of the aquifer and distribution of the parent element in the rock matrix(5). The solubility of radionuclides could affect fluid characteristics (chemical and physical) of the aquifer(5). Rock can be disintegrated or altered by chemical weathering via hydrolysis, oxidation and carbonation(8 – 10). It could occur intensely at a high temperature where heat was originated at depths and transported through water to the earth surface in the fault and fracture zones. Consequently, the concentration of radionuclides in hot spring area depends on the type and abundance of radioactive minerals found in the surrounding rock(10), which indicates the source rock of radionuclides presented in the area. The study area of Khao-Than hot spring is located in the Tha-Chang District, Surat Thani Province, Southern Thailand. It is one of the archaeological, ancient and hot spring natural park sites in Thailand(11, 12). Approximately 738 local people live in the villages nearby the hot spring, with an area of around 47 km2. The number of tourists visiting the hot spring varies
between 5 and 10 persons per day but many more on weekends and holidays(13). The objectives of this study are (i) to determine the natural radioactivity level and analyse for the mineral characteristics in samples in the Khao-Than Hot Spring, (ii) to estimate the radiological characteristics of the sample materials and (iii) to identify the source rock of radionuclides in the area. MATERIALS AND METHOD Geology setting The general geology of the area is predominantly composed of Permo-Carboniferous (CP) and Triassic– Jurassic (TrJ) siliciclastic sedimentary rocks and Jurassic granite (Jgr) (Figure 1). Permian limestone (Pr) hills are located north of and underneath the study area. The Khlong Marui Fault is a major active fault zone in the area lineated predominantly in NNE–SSW directions (Figure 1), where the silicified rocks and carbonate soils were found locally in this zone(11, 12). Sampling and sample preparation Gamma dose survey performed at 1 m above the ground surface in this hot spring area showed that the dose rate ranged from 0.02 to 50 mSv h21, which was used to select the sampling localities (Figure 1). The location of the sampling sites was made using a handheld GPS (GARMIN etrex, USA). The recently deposited soil samples, rock samples and hot spring mud samples of ca. 2 kg each were manually collected from an area of ca. 16 000 m2 in natural and concrete ponds. Sampling interval was separated by a distance of ca. 1 – 10 m apart. The samples were
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
Natural radioactivity in Khao-Than hot spring area, Surat Thani Province, Thailand was investigated. Gamma dose survey indicated a possible high radiation risk for this area. Rock, soil and hot spring mud samples were collected and analysed by a low background gamma spectrometer. The activity concentrations of 226Ra, 232Th and 40K in samples were 151– 139 092 (mean 5 13 794), 12– 596 (127), 24– 616 (215) Bq kg21, respectively. X-ray diffraction and Fourier transform infrared spectroscopy indicated that quartz and calcite (CaCO3) are the main constituents in mud samples with varying contents. In conclusion, this study area was reasonably classified as a high natural background radiation area. The source of radium in this area is supposed to be related to the fault fluids enriched in radium that precipitated with calcium in the carbonate terrain and partly absorbed by high cation exchange capacity clays.
T. BHONGSUWAN AND S. A. AUISUI
kept in plastic bags before transporting them to the laboratory where the samples were crushed into fine powder and then sieved to ,2 mm particle size. The samples were dried in an oven at 1108C for 24 h, then weighed about 200 g each, packed and sealed in an airtight polyvinyl chloride container to prevent the escape of radon(15). The samples were kept sealed hermetically about 4 week to allow radioactive secular equilibrium among the 226Ra, 232Th and their decay products. Mineralogy study (i)
(ii)
X-ray diffraction (XRD): XRD pattern of powdered samples was examined at room temperature by XRD (Phillips X’Pert MPD), Cu-Ka1 radiation (l ¼ 1.5406 A8) tube at 40 kV and current of 30 mA, with the diffraction pattern analysing from 58 to 908 (2u) at a step of 0.028. Mineralogy was identified using the computer program X’-pert High Score Plus(7, 16). Fourier transform infrared spectroscopy (FTIR): The samples for FTIR analysis were dried in an oven at 1008C to remove the moisture. The KBr
pellet technique was used to prepare the samples with the KBr:sample ratio of 100:1. The infrared spectra of sample were measured by an Equinox 55, Bruker spectrophotometer in transmission mode, in the region of 4000–30 cm21, with 2 cm21 resolution(16). Radionuclides measurements The activity concentration of radionuclides 226Ra, 232 Th and 40K in samples was measured using a HPGe coaxial detector (Canberra, Model GC 1319, USA) with an active volume of 59.9 cm3, 1.75 keV full width at half maximum at 1.33 MeV gamma energy. The detector was surrounded by a low background lead shield (Canberra Model 747, USA). The data acquisition and analysis were carried out using a Genie2000 software package (Canberra, USA)(15). The 226Ra, 232Th and 40K were analysed from gamma ray peaks at several energies. Gamma rays from 214Pb (at 295.2 and 351.9 keV) and 214Bi (at 609.3, 1120.3 and 1764.3 keV) were used to determine the 226Ra activity. Gamma rays emitted from 228Ac
Page 2 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
Figure 1. Simplified map of Khao-Than Hot Spring of Surat Thani Province, Southern Thailand with sampling locations. Broken lines indicate traces of Khlong Marui Fault zone(11, 14). CP, Pr, Jgr, TrJ and Q denote Permo-Carboniferous siliciclastic rock, Permian limestone, Jurassic granite, Triassic–Jurassic siliciclastic rock and Quaternary sediment, respectively. Samples named rk3, so45 and so67 are outside the map.
HIGH RADIATION AREA IN KHAO-THAN HOT SPRING
(338.3, 911.6 and 969.1 keV) were used for 232Th, whereas 40K was determined from 1460 keV gamma energy(15). The IAEA CU-2010-03 WWOPT soil sample containing known contents of radionuclides was used for efficiency calibration of the system. The counting time was set to 10 800 s.
RESULTS AND DISCUSSION Mineralogy XRD analysis
FTIR analysis
Figure 2. The XRD patterns of samples m15 and m32 with identified minerals K, kaolinite; C, calcite; Q, quartz and H, halite.
The FTIR spectra of representative samples having varying 226Ra contents are shown in Figure 3. The minerals identified from FTIR include quartz (Q) and calcite (C, CaCO3) with varying contents that are observed from the IR absorption band at 1796– 1807
Figure 3. FTIR spectra of representative samples (sites m15, m21, m24, m30 and m32) and standard minerals, quartz, CaCO3 and kaolinite. Mineral abbreviations include C, CaCO3; Q, quartz; K, kaolinite; M, montmorillonite and O.C., organic carbon(16).
Page 3 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
The XRD spectra of the two representative mud samples from selected sites (sites m15 and m32) are shown in Figure 2. Mud sample m15 contains the highest radium content, while sample m32 has the lowest. XRD spectra indicate that calcite (CaCO3) is the major mineral in sample m15, the highest radium content, whereas quartz (Q), halite (H) and kaolinite (K) are present in sample m32. These minerals are consistent with the geological environment of the study area. Quartz and kaolinite represent the weathering products of Jurassic granite (Jgr) located nearby (Figure 1), whereas calcite (CaCO3) and halite (NaCl) represent dissolution/precipitation of Permian limestone (Pr) and saline intrusion, respectively.
T. BHONGSUWAN AND S. A. AUISUI Table 1. Activity concentrations of 226Ra, 232Th and 40K with their uncertainties in all samples(15). No. Name
m5 m14 m15 m16 m17 m18 m19 m20 m21 m22 m23 m24 m25 m26 m27 m28 m29 m30 m31 m32 m33 rk2 rk3 so8 so9 so10 so44 so45 so67 max min mean
232 Th (Bq kg21)
40 K (Bq kg21)
H
9561+45 4441+31 139 092+188 63 535+127 6841+40 2015+21 2028+23 5375+35 7016+31 3043+28 2307+26 31 439+72 10 538+38 1758+18 2036+19 5227+27 11 713+50 50 221+109 15 873+60 372+8 1150+16 469+15 657+9 1065+27 3139+47 5194+58 10 201+99 151+10 3583+31 139 092+188 151+10 13 794+45
35+9 350+18 596+68 257+34 64+12 48+7 41+6 159+14 99+10 64+9 58+7 243+24 71+12 128+8 22+4 31+5 55+8 124+26 59+11 29+4 140+9 52+15 12+2 45+15 71+31 127+34 408+91 145+13 144+13 596+68 12+2 127+18
233+35 95+16 207+99 150+86 97+22 152+15 191+18 76+17 116+22 306+24 209+22 179+40 281+27 257+19 297+20 283+20 256+33 240+61 252+36 156+12 616+29 24+21 153+11 71+40 40+16 48+87 546+137 571+45 130+18 615+29 24+21 215+36
26 13 38 17 19 6 6 15 19 9 7 86 29 5 6 14 32 13 43 1 4 1 2 3 9 15 29 1 10 38 1 38
Radionuclide concentrations The distribution of the radionuclides 226Ra, 232Th and 40K in all samples is presented in Table 1. Jeasai et al.(17) reported the average concentration of 226Ra in hot spring water from Khao-Than at 2640 mBq l21. The average activity concentrations rank for all samples follows 226Ra . 40K . 232Th as shown in Figure 4. Over 86 % of the analysed samples contain 226 Ra concentrations of .1 kBq kg21. During the course of dose survey using a survey meter at 1 m above ground in this area, the maximum dose rate was found at 50 mSv h21, which corresponded to an effective dose of 438 mSv for a year of exposure. Distribution of 226Ra in all mud samples shows the lowest one in concrete pond (m32; 372 Bq kg21) and the highest in natural pond (m15; 139 092 Bq kg21). The minerals such as montmorillonite, kaolinite and quartz found in mud samples are the result of chemical weathering of Jurassic granite (Jgr) exposed nearby, whereas CaCO3 is originated from dissolution/ precipitation of Permain limestone (Pr) basement underneath the hot spring area. NaCl present in
Figure 4. The relative concentration of 226Ra, 232Th and 40K of the measured samples in the study hot spring.
Page 4 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
226 Ra (Bq kg21)
cm21. Other minerals, kaolinite (K), montmorillonite (M) and organic carbon (O.C.), are also identified from different wave numbers as suggested(7, 16). It can be seen in Figure 3 that radium content in mud samples roughly related to IR absorption intensity of CaCO3 in FTIR spectra. However, the content of high cation exchange capacity (CEC) clays, montmorillonite (M) and the organic carbon (O.C.) in measured samples may play an important role to the total amount of radium in them.
HIGH RADIATION AREA IN KHAO-THAN HOT SPRING
CONCLUSION The results reveal abnormally high concentrations of Ra in mud samples collected from Khao-Than hot spring area. 226Ra is supposed to present in fault fluid in the Khlong Marui Fault that cut across the Jurassic granite nearby and pass underneath this hot spring area. Decomposed granite in the Khlong Marui Fault zone is the most probable source rock of radium in the hot spring area. The XRD and FTIR analyses indicate that quartz and calcite are the major mineral constituents in mud samples together with high CEC montmorillonite and other clays. 226
FUNDING The Department of Physics and Geophysics Research Center, Faculty of Science and the Graduate School, Prince of Songkla University are acknowledged for grant and necessary facilities supports. REFERENCES 1. Onishchenko, A., Zhukovsky, M., Veselinovic, N. and Zunic, Z. S. Radium-226 concentration in spring water sampled in high radon regions. Appl. Radiat. Isot. 68, 825 –827 (2010). 2. Marovic, G., Sencar, J., Franic, Z. and Lokobauer, N. Radium-226 in thermal and mineral springs of Croatia and associated health risks. J. Environ. Radioact. 33, 309 –317 (1996).
3. Beitollahi, M., Ghiassi-Nejad, M., Esmaeli, A. and Dunker, R. Radiological studies in the hot spring region of Mahallat, central Iran. Radiat. Prot. Dosim. 123(4), 505–508 (2007). 4. Bolca, M., Sac, M. M., Altinbas, U. and Camgoz, B. Chemical and radioactivity effects of geothermal springs on environmental pollution in Seferihisar region in western Turkey. Asian J. Chem. 19(3), 2265–2276 (2007). 5. Roba, C. A., Nita, D., Cosma, C., Codreab, V. and Olah, S. Correlations between radium and radon occurrence and hydrogeochemical features for various geothermal aquifers in Northwestern Romania. Geothermics 42, 32– 46 (2012). 6. Dragovic, S. D., Jankovic-Mandic, Lj. J., Dragovic, R. M., Dordevic, M. M. and Dokic, M. M. Spatial distribution of the 226Ra activity concentrations in well and spring waters in Serbia and their relation to geological formations. J. Geochem. Explor. 12, 206–211 (2012). 7. Tabar, E., Kumru, M. N., Sac, M. M., Ichedef, M., Bolca, M. and Ozen, F. Radiological and chemical monitoring of Dikili geothermal waters western Turkey. Radiat. Phys. Chem. 91, 89–97 (2013). 8. Maes, A., Stul, M. S. and Cremers, A. Layer chargecation-exchange capacity relationships in montmorillonite. Clays Clay Miner. 27(5), 387–392 (1979). 9. Uddin, F. Clays, nanoclays, and montmorillonite minerals. Miner. Met. Mater. Soc. ASM Int. 39A, 2804–2814 (2008). 10. Vaculikova, L. and Plevova, E. Identification of clay minerals and micas in sedimentary rocks. Acta Geodyn. Geomater. 2(138), 167–175 (2005). 11. Bhongsuwan, T., Durrast, H., Yordkayhun, S., Nuannin, P. et al. Integrated Geophysical Studies of the Fault Zones in Southern Thailand. Geophysics Research Center, Prince of Songkla University (2013). 12. Chaturongkawanich, S. Geothermal Resources of Changwat Suratthani. Department of Mineral Resources, Thailand (2001). 13. Personnel communication: Khao-Than Sub-District Administrative Organization (2014). 14. Khlong Marui Fault, Active fault map in Thailand, Department of Mineral Resources (2012). 15. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and Effects of Ionizing Radiation: UNSCEAR 2008 Vol. 1. United Nations (2010). 16. Suresh, G., Ramasamy, V., Meenakshisundaram, V., Venkatachalapathy, R. and Ponnusamy, V. A relationship between the natural radioactivity and mineralogical composition of the Ponnaiyar river sediments. India J. Environ. Radioact. 102, 370– 377 (2011). 17. Jeasai, S., Bhongsuwan, T. and Chittrakarn, T. Specific activity of Ra-226 in water from hot springs and nearby shallow wells in Suratthani Province. Kasetsart J. 11(4), 45– 54 (2011).
Page 5 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Manitoba on November 15, 2015
mud samples clearly indicates a result of saline intrusion to the groundwater in the study area that is very close to the sea. Montmorillonite is present in the high-radiumactivity samples (m15, m21, m24 and m30), but it is not present in the lowest radium containing sample (m32). A high CEC of montmorillonite is probably a major cause of absorbed radium in these samples. CaCO3 can be dissolved or precipitated in water, depending on several factors. Consequently, the 226Ra is precipitated together with calcium, forming calcium/radium carbonates in the presence of hot spring. Evidences in the field survey indicated a very high dose in an area where porous carbonates (CaCO3 or limestone) were spreading over the top soil. The texture of this porous CaCO3 indicated precipitation of carbonates from hot spring water. This complex chemical environment represents the characteristics of the study area.
