B B0046 1 © 38 Congress on Science and Technology of Thailand

Home , Chumphon Province, Surat Thani Province

B_B0046 1

MEASUREMENT OF SECIFIC ACTIVITIES OF NATURAL RADIONUCLIDES (40 K, 226 Ra AND 232 Th) IN SURFACE SOIL SAMPLES COLLECTED FROM SURAT THANI PROVINCE IN THE SOUTH OF THAILAND Prasong Kessaratikoon ,1,* Ruthairat Boonkrongcheep,2 Supphawut Benjakul,2 Udorn Youngchauy 3 1Department of Physics, Faculty of Science, Thaksin University, Muang, Songkhla 90000, Thailand 2Research Assistant, Department of Physics, Faculty of Science, Thaksin University, Muang, Songkhla 90000, Thailand 3Research Scientist, Thailand Institute of Nuclear Technology (Public Organization), 16 Vibhavadi Rangsit Rd, Chatuchak, Bangkok 10900, Thailand *e-mail: [email protected]

Abstract: The specific activities of natural radionuclides of 40 K, 226 Ra and 232 Th in 168 surface soil samples collected from 17 districts in Surat Thani provinces in the Southern region of Thailand were measured and analyzed. Concentrations of natural radionuclides in all samples were determined by gamma-ray spectrometer using HPGe detector with specially designed lead-shield. The average specific activities of 40 K, 226 Ra, and 232 Th were determined expressed in Bq/kg. The results show that these three radionuclides were presented in concentrations of 2119.10 ± 171.72, 75.72 ± 5.75 and 47.39 ± 4.76 Bq/kg, respectively. Also the radiological hazard of absorbed dose rate in air (D), radium equivalent activity (Ra eq ), external hazard index (H ex ), and annual effective dose rate (AED out ) in the area under consideration were also calculated. The data were discussed and compared with those given in the literature.

Introduction: Surat Thani province with a name that literally means "City of the Good People" is the largest province in the South of Thailand located 685 kilometers from Bangkok. A former capital of the Srivijaya Empire, the province covers an area of approximately 12,891 square kilometers. Surat Thani Province borders the Gulf of Thailand to the north and east, Chumphon Province to the north, Nakhon Si Thammarat and Krabi Provinces to the south, Phang-Nga and Ranong Provinces to the west and Nakhon Si Thammarat Province to the east as shown in Fig. 1. High plateaus and forested mountains are located to the west of the province, while there are low basins in the center and along the eastern coast. This topography has created 14 river basins and all rivers in Surat Thani flow east of the province to the Gulf of Thailand. The numerous islands along the coast makes Surat Thani a perfect hideaway for vacationers from around the world. The ideal destination for many is the Penang-sized Ko Samui, Thailand's third largest island, and its neighbour Ko Pha-ngan a celebrated island that hosts the biggest beach full moon party. The best time to enjoy one of these islands to the fullest is from April to November. Today, Surat Thani is an important commercial and shipping hub for rubber and coconut trading. According to the 2010 National Power Development Plan implemented in March calls for five nuclear power plants to be built in Thailand, each with a capacity of 1 gigawatt (GW). Two 1GW plants will be set up in 2020 and 2021, followed by the rest from 2024-2025. They will start feeding power to the grid in 2020. Surat Thani is one of three provinces (Chumporn and Nahkon Si Thammarat) in the south of Thailand which was chosen to construct the nuclear power plant in this plan. For this reason, the concentration of natural radioactivity (226 Ra, 232 Th and 40 K) in Surat Thani should be measured and studied before the construction of nuclear power plant. The aim of this paper is to establish reference levels of natural radioactivity for Surat Thani province (Thailand), through the analysis of absorbed dose rate in air (D), radium equivalent activity (Ra eq ), external hazard index (H ex ), and annual effective dose rate

(AED out ) by using high-purity germanium (HPGe) detector and gamma spectrometry analysis system to determine the specific activity of 226 Ra, 232 Th and 40 K in surface soil samples.

Sampling locations

Figure 1. Surat Thani province and sampling locations

(http: // www .ponteethai.com )

Methodology: Surface soil samples (168 samples) were collected from 17 districts (exception on Ko Samui and Ko Pha-ngan districts) of Surat Thani province in the south of Thailand. A map of Surat Thani province and sampling locations is shown in Fig. 1. After collection, each sample was dried up at room temperature and sieved through a 2 mm mesh- sized sieve to remove stone, pebbles and other macro-impurities. All samples were oven dried at a temperature of 100 ◦C for 3 hours, before the analysis for removing moisture. The homogenized sample was placed in a 290 cm 3 PVC containers. The container was sealed hermitically and externally using a cellophane tape and kept aside for about a month to ensure equilibrium between 226 Ra and its daughters and 228 Ra and its daughters before being taken for gamma spectrometric analysis. The specific activities of primordial radionuclides (238 U or 226 Ra, 232 Th and 40 K) in all beach sand samples were determined by employing a high-purity germanium detector (HPGe, CANBERRA Model GC 2018) and gamma spectrometry analysis system at Nuclear and Material Physics Laboratory, Department of Physics, Faculty of Science, Thaksin University. The detector was enclosed in a massive 10 cm thick lead shielding. Gamma ray radioactive standard sources Cobalt-60 (Co-60), Cesium-137 (Cs-137) and Barium-133 (Ba-133) were used to calibrate the measurement system up to about 2 MeV. Geometric efficiency for beach sand matrices in the container was determined by an IAEA/RGU-1, IAEA/RGTh-1and KCL reference material (International Atomic Energy Agency IAEA, Vienna, Austria). The spectra were analyzed using the program GENIE 2000. The specific activity of 40 K was determined from its 1460.8 keV γ- line. The specific activities of 226 Ra and 232 Th were determined by their decay products 214 Pb (351.9 keV) and 208 Tl (583.2 keV), respectively. The specific activity of 137 Cs was also determined from its 661.7 keV γ-line. Counting time interval was 10,800 s. The background spectrum was recorded immediately after or before the sample counting.

Results, Discussion and Conclusion: The range and average values of specific activities of 40 K, 226 Ra and 232 Th in 168 surface soil samples collected from Surat Thani province (Thailand) were calculated and presented in Table 1.

Table 1. Range and average value of specific activities of 40 K, 226 Ra and 232 Th in 168 surface soil samples collected from Surat Thani province (Thailand).

Surface soil samples Specific Activities (Bq/kg)

in Surat Thani (168 samples) 40 K 226 Ra 232 Th

Muang 2465.12 ± 184.56 57.14 ± 5.47 50.86 ± 4.88 Phunphin 1579.57 ± 162.32 64.26 ± 5.96 39.38 ± 4.86 Don Sak 1997.89 ± 182.57 39.11 ± 5.06 40.14 ± 4.48 Kanchanadit 3176.25 ± 252.96 114.32 ± 7.37 84.01 ± 6.29 Ban Na doem 1408.05 ± 135.63 68.38 ± 5.67 39.58 ± 4.14 Ban Na San 4014.84 ± 243.90 155.96 ± 8.30 68.33 ± 5.61 Wiang Sra 2211.82 ± 185.08 118.38 ± 7.30 64.91 ± 5.95 Kian Sa 523.87 ± 85.22 35.86 ± 3.99 27.50 ± 3.27 Phrasaeng 639.08 ± 94.58 36.01 ± 4.04 24.70 ± 3.32 Chaiburi 582.29 ± 87.54 29.43 ± 3.46 18.93 ± 2.74 Ban Ta Khun 1054.98 ± 125.71 40.05 ± 4.52 36.10 ± 6.70 Phanom 1895.09 ± 159.11 36.42 ± 4.49 40.20 ± 4.20 Khiri Ratthanikhom 2358.32 ± 192.66 151.82 ± 7.58 66.78 ± 5.44 Wipawadi 1385.63 ± 150.78 43.04 ± 4.24 19.04 ± 2.39 Tha Chana 3543.17 ± 213.80 106.79 ± 6.75 54.53 ± 5.15 Chaiya 4169.09 ± 229.92 94.36 ± 6.61 70.30 ± 5.72 Tha Chang 3019.63 ± 232.95 95.98 ± 6.86 60.25 ± 5.84 Ko Samui - - - Ko Pha-ngan - - - Range 32.53 – 11691.63 10.64 – 704.75 3.52 – 300.51 Average value 2119.10 ± 171.72 75.72 ± 5.75 47.39 ± 4.76

The average value of the specific activities of 40 K, 226 Ra and 232 Th in 168 surface soil samples collected from Surat Thani province (Thailand) were also compared with data in Southern of Thailand, OAP data and worldwide mean as shown in Table 2.

Table 2 . Comparison of the average value of specific activities of 40 K, 226 Ra and 232 Th in 168

surface soil samples collected from Surat Thani province (Thailand) with those in Southern of

Thailand, OAP data and wor ldwide mean.

Specific Activities (Bq/kg) Data Sources

40 K 226 Ra 232 Th

Songkhla 3562.14 ± 223.56 107.28 ± 6.74 51.53 ± 5.02 NaKhon Si Thammarat 4313.18 ± 148.16 108.55 ± 31.19 73.95 ± 4.15 Phatthalung 3573.35 ± 203.89 135.89 ± 6.71 76.34 ± 5.32

Trang 384.85 ± 23.30 76.48 ± 3.38 84.38 ± 4.53 Phuket 4092.29 ± 267.05 212.55 ± 10.18 203.98 ± 9.58 Satun 4020.90 ± 246.55 98.75 ± 6.76 63.63 ± 2.34 Surat Thani 2119.10 ± 171.72 75.72 ± 5.75 47.39 ± 4.76 Southern of Thailand 511.04 ± 7.04 171.5 ± 3.13 211.19 ±1.98 Thailand Mean (OAP) 400 48 40 Worldwide Mean 400 35 30

From the result in Table 2, the average specific activities of 40 K in Surat Thani is lower than in Songkhla, Nakhon Si Thammarat, Phatthalung, Phuket and Satun provinces but higher than in Trang province. The average specific activities of 226 Ra and 232 Th in Surat Thani are lower than in Songkhla, Nakhon Si Thammarat, Phatthalung, Trang, Phuket and Satun provinces. We can also see that the average specific activities of 40 K, 226 Ra and 232 Th in Surat Thani are always higher than the data from the Southern of Thailand, Thailand and worldwide Means. By using the specific activity values of 40 K, 226 Ra, and 232 Th as shown in Table 1, The absorbed dose rates in air (D), the radium equivalent activity (Ra eq ), the external hazard index (H ex ) and the annual effective dose rate can be evaluated and presented in Table 3.

Table 3. Gamma absorbed dose rate, radium equivalent activity, external hazard index, and annual effective dose rate of 168 surface soil samples collected from Surat Thani province (Thailand) . Gamma Radium Annual External absorbed equivalent effective dose Locations hazard dose rate activity rate index (nGy/h) (Bq/kg) (mSv/y) Muang 159.91 ± 13.17 319.43 ± 26.64 0.86 ± 0.07 0.20 ± 0.02 Phunphin 116.05 ± 12.12 235.94 ± 24.76 0.64 ± 0.07 0.14 ± 0.01 Don Sak 125.63 ± 12.66 250.14 ± 25.50 0.68 ± 0.07 0.15 ± 0.02 Kanchanadit 229.99 ± 17.27 467.56 ± 34.93 1.26 ± 0.09 0.28 ± 0.02 Ban Na doem 114.22 ± 10.78 233.24 ± 22.02 0.63 ± 0.06 0.14 ± 0.01 Ban Na San 280.74 ± 17.39 562.41 ± 35.07 1.52 ± 0.09 0.34 ± 0.02 Wiang Sra 186.13 ± 14.68 381.24 ± 30.03 1.03 ± 0.08 0.23 ± 0.02 Kian Sa 55.02 ± 7.37 115.44 ± 15.22 0.31 ± 0.04 0.07 ± 0.01 Phrasaeng 58.21 ± 7.82 120.46 ± 16.06 0.33 ± 0.04 0.07 ± 0.01 Chaiburi 49.31 ± 6.90 101.27 ± 14.10 0.27 ± 0.04 0.06 ± 0.01 Ban Ta Khun 84.30 ± 11.38 172.78 ± 23.76 0.47 ± 0.06 0.10 ± 0.01 Phanom 117.43 ± 10.97 233.24 ± 22.07 0.63 ± 0.06 0.14 ± 0.01 Khiri Ratthanikhom 208.82 ± 14.82 428.62 ± 30.18 1.16 ± 0.08 0.26 ± 0.02 Wipawadi 69.91 ± 7.60 141.31 ± 15.40 0.38 ± 0.04 0.09 ± 0.01 Tha Chana 215.25 ± 14.25 429.98 ± 28.91 1.16 ± 0.08 0.26 ± 0.02 Chaiya 259.91 ± 16.10 515.49 ± 32.47 1.39 ± 0.09 0.32 ± 0.02 Tha Chang 206.65 ± 16.41 414.33 ± 33.13 1.12 ± 0.09 0.25 ± 0.02 Ko Samui - - - - Ko Pha-ngan - - - - Ranges 11.85 - 725.25 26.42 - 1483.00 0.07 - 4.01 0.01 - 0.89 Average Values 149.26 ± 12.45 301.35 ± 25.31 0.81 ± 0.07 0.18 ± 0.02

UNSCEAR 55 370 1 0.48 (1988, 1993, 2000)

From Table 3, we can see that the average value of gamma dose rate obtained in this study (149.26 nGy/h) is larger than about three times to the world average (55 nGy/h). The average values of radium equivalent activity ( 301.35 Bq/kg ) are less than 370 Bq/kg, which are acceptable for safe use. The average values of external hazard index obtained in this study was found to be 0.81 which is equal to unity. The calculated annual effective dose with average value 0.18 mSv/y is lower than the worldwide average value (0.48 mSv/y). This means that the radiation hazard is still insignificant for the population living in the investigated area.

References: 1. Beretka J, Mathew PJ. Health Phys 1985; 48: 87-95. 2. Mohanty AK, Sengupta D, Das SK, Vijayan V, Saha SK. Radiat Meas 2004; 38: 153- 165. 3. Singh S, Rani A, Mahajan RK. Radiat Meas 2005; 39: 431-439. 4. United Nations Scientific Committee on the Effects of Atomic Radiation 1993; UNSCEAR New York. 5. Veiga R, Sanches N, Anjos RM, Macario K, Bastos J, Iguatemy M, Aguiar JG, Santos AHA, Mosquera B, Carvalho C, Baptista Filho M, Umisedo NK. Radiat Meas 2005; 41:189-196.

Acknowledgements: The investigation was fully supported by Research and Development Institute Thaksin University (RDITSU). The authors would like to thank Department of Physics, Faculty of Science, Thaksin University for allowing us to use all instruments and radioactive standard sources at Nuclear and Material Physics Laboratory. The authors wish to thank Assoc. Prof. Dr.Tripop Bhongsuwan, Head of Department of Physics, Faculty of Science, Prince of Songkhla University(PSU), Hat Yai Campus for his generous permission to us to use the standard reference materials (IAEA/RGU-1 IAEA/RGTh-1 and KCL) for calculation and analysis in this study. The authors are particularly indebted to some of undergraduate and graduate students for their works and patience in samples collection, measurement and analysis some parts of these data.

Keywords: specific activity, natural radionuclide, gamma-ray spectrometer, HPGe detector, radiological hazard, absorbed dose rate in air, radium equivalent activity, external hazard index, annual effective dose rate