Project name: Assessment of natural radioactivity in some building materials used in laos pdr

ginning with naturally occurring uranium-238, this series includes the following elements: astatine, bismuth, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least transiently, in any natural uranium-containing sample, whether metal, compound, or mineral. The series terminates with lead-206. The decay scheme of this series is presented in Figure 1.1 (1) 238 U 4,468×10 9 y năm ↓ α (2) 234 Th 24,1 ngày ↓ β (3) 234 Pa 1,17 phút ↓ β (4) 234 U 2,455×10 5 năm ↓ α (5) 230 Th 7,538 ×10 4 năm ↓ α (6) 226 Ra 1600 năm ↓ α (7) 222 Rn 3,8232 ngày ↓ α (8) 218 Po 3,094 phút ↓ α (9) 214 Pb 26,8 phút ↓ β (10) 214 Bi 19,9 phút ↓ β (11) 214 Po 162,3 giây 3 ↓ α (12) 210 Pb 22,3 năm ↓ β (13) 210 Bi 5,013 ngày ↓ β (14) 210 Po 138,4 ngày ↓ α 206 Pb Figure 1.1. The decay scheme of the 238 U series. Nuclides underlined are measurable by gamma-ray spectrometry. b) The actinium series - 235 U Beginning with the naturally-occurring isotope U-235, this decay series includes the following elements: actinium, astatine, bismuth, francium, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least transiently, in any sample containing uranium-235, whether metal, compound, ore, or mineral. This series terminates with the stable isotope lead-207. The decay scheme of this series is shown in Figure 1.2. (1) 235 U 1,7×10 8 năm ↓ α (2) 231 Th 25,52 giờ ↓ β (3) 231 Pa 3,276 ×10 4 năm ↓ α (4) 227 Ac 21,772 năm ↓ β (5) 227 Th 18,718 ngày + α (1,38 %) to 223Fr 22 phút then β ↓ α (6) 223 Ra 11,43 ngày ↓ α (7) 219 Rn 3,96 giây ↓ α (8) 215 Po 1,781 giay ↓ α (9) 211 Pb 36,1 phút ↓ β (10) 211 Bi 2,14 phút ↓ α (11) 207 Tl 4,77 phút + β (0,273%) 211Po 516 giây then α ↓ β 207 Pb Figure 1.2. The decay scheme of the 235 U series. Only 235 U is measurable by gamma-ray spectrometry. 4 c) The thorium series 232 Th Beginning with naturally occurring thorium-232, this series includes the following elements: actinium, bismuth, lead, polonium, radium, radon and thallium. All are present, at least transiently, in any natural thorium-containing sample, whether metal, compound, or mineral. The series terminates with lead-208. The decay scheme of this series is shown in Figure 1.3. (1) 232 Th 1,405 ×10 9 năm ↓ α (2) 228 Ra 5,75 giờ ↓ β (3) 228 Ac 6,15 giờ ↓ β (4) 228Th 1,9127 năm ↓ α (5) 224 Ra 3,627 ngày ↓ α (6) 220 Rn 55,8 giây ↓ α (7) 216 Po 150 giây ↓ α (8) 212 Pb 10,64 giờ ↓ β (9) 212 Bi 60,54 phút ↓ β (64,06%) ↓ α (35,94%) (10) 212 Po 0,3 giây 208 Tl 3,06 phúg ↓ α ↓ β 206 Pb Figure 1.3. The decay scheme of the 232 Th series. Nuclides underlined are measurable by gamma-ray spectrometry. 1.1.2. Radon loss 1.1.3. Natural disturbance of the decay series 1.2. Effects of radiation hazards from building material to health body 1.3. Research condition of radiation in building material in the world In most countries, the inspection and assessment of the level of radioactivity in building materials are mandatory. To understand more about this issue, we have listed some recent works about natural radioactivity in different types of building Materials conducted by scientists in some countries in the world. The available data of specific radio-activities of some common building materials in some countries taken from literatures are presented in the tables numbered as 1.1, 1.2 and 1.3 below. 5 Table 1.1. The activity concentration (Bq.kg -1 ) Portland cement samples for different countries in the world. Countries Activity concentration (Bq.kg -1 ) References 226 Ra 232 Th 40 K Greece 92 31 310 [12] Austria 26.7 14.2 210 [13] Bangladesh 60.5 64.7 952.2 [14] China 56.50 36.50 173.2 [15] Egypt 134 88 416 [16] Pakistan 31.3 26.8 51.3 [17] Turkey 40.5 26.1 267.1 [18] Ghana 61.63 25.96 451.30 [19] India 37.0 24.1 432.2 [20] Malaysia 34.7 32.9 190.6 [21] Brazil 61.7 58.5 564.0 [22] Lao PDR 41.12 16.60 141.48 [23] Table 1.2. Comparison between the activity concentrations of our building materials with that of other countries of the world S. No Countries materials Activity concentration (Bq.kg - 1 ) Raeq (Bq.kg -1 ) References 226 Ra 232 Th 40 K 1 Australia brick 41 89 681 220,71 [24] [24] [24] Soil 62.9 162.8 403.3 326.76 Sand 3.7 40 44.4 64.32 2 China brick 124.7 28.9 390.2 196.07 [25] [26] [15] Soil 44.6 86.7 352.8  195.75 Sand 40.7 21.5 302.6 96.4 3 Egypt brick 24 24.1 258 78.33 [27] [28] [29] Soil 13 6 433 54.92 Sand 9.2 3.3 47.3 17.56 4 Brazil brick 16.2 70 76 122.15 [30] [31] [30] Soil 30 67 112 134.43 Sand 35.3 74 315 165.38 5 Pakistan brick 43.2 53.7 631.2 168.59 [17] [17] [17] Soil 42.4 56.2 565.3 166.29 Sand 21.5 31.9 519.6 107.13 6 India brick 63.74 38.6 313.71 143.09 [32] Soil 116.1 43.51 300.07 201.44 [32] Sand 90.27 101.67 280.71 257.27 [32] 7 World- wide brick 35 30 400 [33] Soil 35 30 400 [33] Sand 35 30 400 [33] 6 Table 1.3. The specific radio-activities of 40 K, 226 Ra and 232 Th in building materials used in Ha Noi S. No. Building materials Activity concentration K-40 Ra-226 Th-232 1 Black sand 515 ± 23 24.4 ± 1,4 36,2 ± 1.0 2 khuyến lương Sand 483 ± 15 53,5 ± 3,7 46 ± 3.6 3 yellow sand 651 ± 21 25,5 ± 0,9 32,3 ± 0.6 4 Hà Bắc yellow sand 357 ± 2 12,4 ± 2,5 20 ± 2,4 5 Hải Phòng cement 73 ± 9 28,6 ± 2,5 32,3 ± 2,8 6 Hoàng Thạch cement 196 ± 2 65,9 ± 3,7 27,8 ± 2,8 7 X77 cement 205 ± 2 69,6 ± 3,7 32,2 ± 2,8 8 Gravel 389 ± 8 23,5 ± 5 23 ± 4 9 Rock 46 ± 21 25,5 ± 5 19 ± 4 10 Brick 665 ± 0 84,0 ± 15 85 ± 4 11 Tiles 385 ± 5 39 ± 8 34 ± 4 12 Plaster 525 ± 5 44 ± 4 37 ± 4 13 Rock dust < 10 12,4 ± 2,5 6,8 ± 2,4 14 Tro xỉ hồ chứa 626 ± 3 122 ± 9 100 ± 15 Fly ash 788 ± 7 164 ± 13 126± 1 1.4. Investigation of Radioactivity in the building materials in Laos PDR In recent years, the economy of Laos has continuously grown and developed in a stable speed, with GDP increasing by an average of 7.6%; Per capita income has reached nearly 1,700 USD in the period 2013-2014. These achievements facilitate the Lao Government to successfully implement the 7th Socio-Economic Development Plan this year as well as the Millennium Development Goals. Along with economic development, the demand for construction is rising significantly, leading to the establishment of various construction materials companies. Nevertheless, because the scientific level of the Lao People's Democratic Republic is still at a very modest level and lack of human resources to undertake, the inspection of natural radioactivity in construction materials so far has not been conducted. The researchers were also encouraged to choose any topic that is related to natural radioactivity survey in Building Materials, which aims to widely expand this research direction in Laos PDR. This thesis may be considered as the first work in this direction in Laos PDR. 7 CHAPTER 2 GAMMA SPECTROCOPY USING EITHER HPGe AND NaI(Tl) SCINTILLATION DETECTOR 2.1. Physics foundation of gamma-ray detection with scintillation and HPGE Detectors 2.1.1. Interaction Of Gamma Radiation With Matter 2.1.2. Photoelectric effect 2.1.3. Compton Scattering 2.1.4. Pair Production 2.1.5. Attenuation of Gamma Radiation with matter 2.2. Configuration and gamma ray spectroscopy of NaI(Tl) and HPGe detector principles 2.3. HPGe Detector: Gamma-ray spectrum structure 2.3.1. Operational principles of HPGe detectors 2.3.2. Configurations of HPGe detectors 2.3.3. Gamma ray spectroscopy with HPGe detector 2.4. Scintillation detector: Gamma-ray spectrum structure 2.4.1. Configuration of Scintillation detectors 2.4.2. Gamma ray spectroscopy with Scintillation Detector CHAPTER 3 EXPERIMENTAL METHODS 3.1. Selection of sampling point of building materials Four kinds of building materials commonly used in Laos PDR including cement, sand, brick and soil have been chosen in this thesis. 3.1.1. Cement samples collection Figure 3.1. The map of Lao PDR showing the local famous cement factories in Lao PDR (from which the cement samples were collected). 8 Table 3.1. The labels of the analyzed cement samples. S. No Symbol Type of cement Map icon Position Latitude (°N) Longitude (°E) 1 1V1 Porland cement (1V) A 18°56'7.6"N 102°27'7.0"E 2 1V2 3 1V3 4 1V4 5 1V5 6 1V6 7 1V7 8 2V1 Mixed cement (2V) 9 2V2 10 2V3 11 2V4 12 2V5 13 2V6 14 2V7 15 1VT1 Mixed cement (1VT) B 18°6'27.3"N 102°47'7.9"E 16 1VT2 17 1VT3 18 2VT1 Porland cement (2VT) 19 2VT2 20 2VT3 21 2VT4 22 1K1 Porland cement (1K) C 17°24'19.8"N 105°12'58.2"E 23 1K2 24 1K3 25 1K4 26 2K1 Mixed cement (2K) 27 2K2 28 2K3 29 2K4 30 1SV1 Porland cement (1SV) D 15°50'39.1"N 106°23'16.4"E 31 1SV2 32 1SV3 33 1SV4 34 2SV1 Mixed cement (2SV) 35 2SV2 36 2SV3 37 2SV4 9 3.1.2. Soil sample selection Figure 3.2. The map of Lao PDR showing the Thoulakhom district and the soil and sand sampling locations were indicated as P1, P2, , P10. Table 3.2. The labels of the analyzed soil samples. S. No Symbol Village Position Latitude (°N) Longitude (°E) 1 1P1 Ban Dong (P1) 18°16'52.5" N 102°40'51.5"E 2 1P2 3 1P3 4 2P1 Ban PhaThao (P2) 18°19'40.5" N 102°39'56.5"E 5 2P2 6 2P3 7 3P1 Ban Nam Ang (P3) 18°22'23.9" N 102°36'5.4"E 8 3P2 9 3P3 10 4P1 Ban Nanokkhoum (P4) 18°17'18.2" N 102°41'35.8"E 11 4P2 12 4P3 13 5P1 Ban Phonmouang (P5) 18°20'15.7" N 102°40'51.4"E 14 5P2 15 5P3 16 6P1 Ban NaKang (P6) 18°20'42.0" N 102°39'40.4"E 17 6P2 18 6P3 19 7P1 Ban Naxanglek (P7) 18°21'54.5" N 102°37'48.8"E 20 7P2 21 7P3 22 8P1 Ban Keun (P8) 18°21'51.2" N 102°35'13.3"E 10 23 8P2 24 8P3 25 9P1 Ban Hatnoi (P9) 18°22'58.6" N 102°33'52.5"E 26 9P2 27 9P3 28 10P1 Ban Boungphao (P10) 18°20'49.3" N 102°33'59.6" 29 10P2 30 10P3 3.1.3. Sand samples preparation Figure 3.3. Map of Vientiane capital showing the Mekog river and locations of sand samples discussed in this preliminary study Figure 3.4. Photo of river sand in Mekong driver in Vientiane capital Figure 3.5. River sand Namngeum in Thoulakhom district, Vientiane province. 11 Table 3.3. The labels of the analyzed cement samples. S. No Symbol Village Position Latitude (°N) Longitude (°E) 1 1NK1 Ban HuayYai (NK1) 18°56'7.6"N 102°27'7.0"E 2 1NK2 3 1NK3 4 1NK4 5 1NK4 6 2Nk1 Ban HuayHom(NK2) 18°6'27.3"N 102°47'7.9"E 7 2NK2 8 2Nk3 9 2Nk4 10 3NK1 Ban NongDa(NK3) 17°58'22.7"N 102°30'8.9"E 11 3NK2 12 3NK3 13 3NK4 14 4N1 Ban Don Chan(NK4) 17°57'57.0"N 102°35'47.3" 15 4NK2 16 4NK3 17 4NK4 18 5NK1 Ban Hom1(NK5) 17°50'10.8"N 102°35'58.8" 19 5NK2 20 5NK3 21 5NK4 22 6NK1 Ban Hom2(NK6) 17°51'16.5"N 102°35'37.8" 23 6NK2 24 6NK3 25 6NK4 26 1NG1 Ban Keun (P11) 18°21'30.7"N 102°34'19.3"E 27 1NG2 28 1NG3 29 NG4 30 2NG1 Ban Pakchan (P12) 18°22'15.1"N 102°32'10.7"E 31 2NG2 32 2NG3 33 2NG4 12 Figure 3.6. Square flame of 100cm × 100cm. 3.1.4. Brick sample selection 3.2. Preparation of sample for analysis Before analysis, the collected samples have to be prepared for measurement. The sample preparation procedure is presented below in figure 3.6. Figure 3.6. The schematic of the process of sample preparation. Figure 3.7 is a picture for illustration of the sample preparation process. A mortar and pestle for crushing and homogenizing and a standard sieve of 0.2 mm mesh size have been used for sample preparation. The prepared building materials finally were filled in the beakers sealed with plastic tape to prevent the escape of airborne radionuclides. The pictures of some prepared samples are presented in figure 3.8. 13 Figure 3.7. A mortar and pestle for crushing and homogenizing. A standard sieve of 0.2 mm mesh zize. Figure 3.8. A prepared building materials were filled in the beaker sealed with plastic tape to prevent the escape of airborne radionuclides. 3.3. Reference materials Figure 3.9. Picture of Three reference materials, obtained from the International Atomic Energy Agency (IAEA: RGU-1, RGTh-1 and RGK-1). For determination of the specific radioactive concentrations of the materials, the relative method has been used. For this, the reference materials obtained for IAEA have been used. The picture of these reference materials including RGU-1, RGTh-1 and RGK-1 is shown in figure 3.9 together with their data listed in Table 3.4. Table 3.4. The table shows the data of reference material used. Sample Mass (g) Density (g/cm 3 ) Mass acivity (Bq/kg) IAEA-RGK-1 340,91 1,8 14000±400 IAEA-RGU-1 378,82 1,94 4940±30 IAEA-RGTh-1 309,01 1,736 3250±90 14 3.4. Method of Determination of activity concentrations of natural radionuclides from gamma-ray spectra with Scintillation detectors Figure 3.10 is the pictures of the gamma-ray spectrometers used in our work. On the left panel is the spectrometer using NaI(Tl) detector while on the right panel is the spectrometer using HPGe detector. Fig. 3.10. Picture of gamma-ray spectroscopy using Scintillation Detector. For determination of activity of the naturally occurring radioactive isotopes using NaI(Tl) detector, we have used a method for overcoming the poor energy resolution of NaI(Tl) detector. The method is based on the characteristics of the IAEA reference materials used in our investigation. Firstly, we need to measure the spectra of background, RGU-1, RGTh-1 and GRK-1 reference samples. These spectra are presented in figure 3.11. Fig. 3.11. a) Background Spectrum, obtained in a collecting time for 52700 second. b) Spectrum of IAEA RGU-1 was collected for 13942 second. c) Spectrum of IAEA-RGTh-1 was collected for 18190second. d) Spectrum of IAEA-RGK-1 was collected for 17215 second. Based on these spectra, we defined the energy region of interest (ROI) for our interested isotopes, which is written in table 3.5. 15 Table 3.5. Energy windows for determination of concentration of naturally occurring radioactive isotopes using the gamma spectrometer with NaI(Tl) detector. Parent isotope Daughter isotope Gamma ray energy (keV) Energy window (keV) 1 238 U 214 Bi 1764,49 1632 – 1897 2 232 Th 208 Tl 2614,53 2418 – 2811 3 40 K 40 K 1460,8 1351 - 1570 The following algorithm was used to determine the concentration of radioactive isotopes, which is explained below. The net count rate in the ith Roi of a calibration standard j (with i and j equal to 1, 2 and 3 denoting the ROIs, and the calibration standards of K, U and Th, respectively) is proportional to the activity An,j of each investigated nuclide n (n=1,2 and 3 for 40 K, 238 U and 232 Th, respectively) according to: ∑ (3.1) Where is the counting efficiency in the ith. ROI for the nuclide n. the net count rate is given by R t N bi j ji ji , , ,  (3.2) Thus, AK, ATh và AU can be obtained by solving the system of simultaneous equations: AeAeAe ThUKK 3,12,11,1  AeAe ThUU 3,22,2  AeAe ThUTh 3,32,3  (3.3) From the RGK-1 standard, on has: A e 1,1 1,1 1,1   (3.4) From the RGU-1 standard: A e 2,2 2,1 2,1   A e 2,2 2,2 2,2   (3.5) And from the RGTh-1 standard: A A A e 3,3 3,2 2,2 2,1 3,1 3,1     (3.6) 16 A A A e 3,3 3,2 3,2 2,2 3,2 3,2     The other constant can be obtained by combining the count rates for the U and Th standards in the third ROI: A e 2,2 2,3 2,3   A A A e 3,3 3,2 2,2 2,3 3,3 3,3     (3.7) Giá trị của các hoạt độ trong các mẫu chuẩn của IAEA là: A11=9869 Bq, A12=129.55 Bq, A13=0.07 Bq, A22=3527 Bq, A23=18 Bq và A33=2298 Bq. Table 3.6. Counting efficiency values, determination from spectrum of reference materials (IAEA) e11 e12 e13 e22 e23 e32 e33 7,216327 x 10-4 1,033662 x 10-4 -2,413112 x 10-4 7,927624 x 10-4 -4,421488 x 10-4 -2,433944 x 10-5 1,29643 x 10-3 The concentration of 238 U, 232 Th and 40 K isotopes are calculated using the following equations: e e e e ee A ThU Th 2,3 3,3 2,2 3,2 2,32,2     (3.8) A e e e A Th U U 2,2 3,2 2,2  (3.9) A e e A e e e A ThU K K 1,1 3,1 1,1 2,1 1,1  (3.10) The standard uncertainty on the activity values, can be calculate as   1/2 1,1 1,1 1 K t b t A N Re      2/1 ,22 2,2 1 RN e b t A t U    2/1 ,33 3,3 1 RN e b t A t Th  (3.11) A computer program has been written to determine these coefficients. Its flow chart is shown in the in Figure 3.12. 17 Fig. 3.12. Computer flow chart showing the automatic determination of activity concentrations of natural radionuclides from gamma-ray spectra with NaI(Tl) detector. 3.5. Determination of activity concentrations of natural radionuclides from gamma-ray spectra with HPGe detectors Two method for measurement of radioactive concentration: Relative method and absolute method. Before measurement of radioactivity concentration in the samples, we have to perform some calibration including energy, resolution and efficiency calibrations. 3.5.1. Data analysis when used relative method of determination of the specific activity for the natural radioactive isotopes 18 3.5.2. Relative method of Determination of the Specific Activity of the naturally occurring radioactive isotopes The activity concentrtion of the naturally occurring radioactive isotopes in the investigated samples is given by the following equation [72]: (3.20) where: Am and AS are the activity concentrations of the cement and reference samples in Bq.kg -1 ; Cm and CS are the count rates obtained under the corresponding peak of cement sample and reference samples in counts.s -1 ; Mm and MS are masses of the cement and reference samples in kg; tm and tS are the measuring live times for the cement and reference samples (s); T1/2,i is the half-life of the radionuclide. The error of the specific activities is calculated using the following formula: √( ) ( ) ( ) ( ) ( ) (3.21) 3.6. Assessment of Radiological Hazard 3.6.1. Radium equivalent activity (Raeq) The most widely used radiation hazard index is called the radium equivalent activity Raeq, which is a weighted sum of activities of the 3 radionuclides 226 Ra, 232 Th and 40 K. It has been calculated by the following equation: ( ) ( ) (3.22) Where ARa, ATh and Ak are the activity concentrations of 226 Ra, 232 Th, and 40 K in Bq.kg -1 , respectively. 3.6.2. External and internal hazard indexes (Hex and Hin) A widely used hazard index (reflecting external exposure) called the external hazard index Hex is defined as follows: ex Ra 370 Th 259 4810 (3.23) Radon and its short-lived product are also hazardous to the respiratory organs. The internal exposure to radon and its daughter progenies is quantified by the internal hazard index Hin, which is given by the equation: Ra Th 259 4810 (3.24) The values of the indices (Hex, Hin) must be less than unity for radiation hazard to be negligible. 3.6.3. Absorbed dose rate in air (D) The activity concentrations of 226 Ra, 232 Th and 40 K were used to calculate the total external absorbed dose rate DR in nGy.h -1 to the general public in outdoor air at 1 m above the earth’s surface was calculated as follows: (3.25) 19 The safe threshold value of DR is 80 nGy.h -1 . 3.6.4. Annual effective dose equivalent (AEDE) The annual effective dose equivalent (AEDE) resulting from the ingestion of the radionuclides in the samples was estimated using following equation: (3.26) CHAPTER 4 EXPERIMENTAL RESULTS AND DISCUSSION 4.1. Energy calibration The energy calibration of the gamma spectrometry set-up in the current work was performed using four differnence sources: 22 Na, 137 Cs, 60 Co and 152 Eu. The energy calibration curve can be calculated using the equation below : (4.1) Fig.4.1. The Spectrum and Gamma-ray effiency calibration: a), b) The Spectrum and detector efficiency calibration (used 137Cs and 60Co, standard source) for the NaI(Tl) detector. c), d). The Spectrum and efficiency calibration (used 152Eu standard source) for HPGe detector. 4.2. Experimental efficiency calibration for a HPGe detector The absolute, full-energy peak efficiency can be defined as follows [4.2]: (4.2) The kit standard a reference sample which IAEA-RGU-1 have been used perform the standard curve of efficieny for HPGe detector. It’s show 5 polynomial function (4.3) 20 Figure 4.2. Detector Efficiency calibration susing IAEA-RGU-1 reference materials. Table 4.2. Values and standard devirations of A0, A1, A2, A3, A4, A5 parameters Value Uncertainty A0 0.0296 4.72E-04 A1 -8.16E-05 2.62E-06 A2 1.05E-07 4.95E-09 A3 -6.64E-11 4.20E-12 A4 2.03E-14 1.64E-15 A5 -2.41E-18 2.39E-19 4.3. Determination of activity concentrations of natural radionuclides in building materials from gamma-ray spectra with HPGe detectors The acquisition time is 72 000s for background, reference and samples respectively. The activity concentration in Bq kg -1 of the natural radionuclides of the collected cement samples were determined by a high resolution gamma-ray spectrometry using a p-type high purity germanium (HPGe) detector model with crystal diameter 53 mm, crystal length 54.7mm of the ORTEC company, and the relative efficiency 20% and the energy resolution (FWHM) at 1332 keV ( 60 Co) is 1.8 keV, which is connected to a spectroscopy amplifier model 572A (ORTEC) and a computer based PCA-MR 8192 ACCUSPEC multichannel analyzer. The MAESTRO-32 multi-channel analyzer emulation software was used for data acquisition, storage, display, online and offline analysis of the gamma-spectra. 4.4. Activity concentration of building materials 4.4.1. The activity concentration results for the cement samples are measured by gamma-ray spectra with HPGe detectors 21 Table 4.4. The results of the average activity concentrations of 238 U, 232 Th and 40 K in cement samples using spectrometry with HPGe detector. Sample Activity concentration in Bq kg -1 238 U (Bq.kg -1 ) 232 Th (Bq.kg -1 ) 40 K (Bq.kg -1 ) 1V 39.48±0.86 9.83±0.76 156.92±3.76 2V 38.94±0.86 9.47±0.75 61.76±2.66 1VT 33.28±1.26 17.21±1.35 131.93±5.48 2VT 29.41±1.05 20.96±1.23 168.70±5.08 1K 28.96±1.07 20.59±1.27 141.83±4.94 2K 25.76±1.16 16.20±1.19 111.28±4.63 1SV 53.19±1.24 7.73±0.98 45.22±3.64 2SV 49.52±1.24 4.74±0.86 39.32±3.50 Average value 37.32±0.3746 13.34±0.3673 107.12±1.4861 World average 35 30 400 4.4.2. Determination of activity concentrations of natural radionuclides in cement samples using gamma-ray spectrometry with Scintillation detectors Table 4.6. The average activity concentrations of 238 U, 232 Th and 40 K in some cement samples are measured using by NaI(Tl) detector and automatic measurement using by computer program QB64 Sample Activity concentration in Bq kg -1 238 U 232 Th 40 K 1V 63.22 12.06 157.43 2V 65.02 13.51 130.38 1K 49.58 47.11 114.03 2K 54.45 30.62 94.09 4.4.3. The activity concentration results for the soil samples were using gamma-ray spectra with HPGe detectors Table 4.7. Average activity concerntration (Bq kg -1 ) in soil samples Sample Activity concentration in Bq kg -1 238 U 232 Th 40 K P1 11.28±0.90 7.43±1.05 40.52±3.88 P2 25.94±1.13 29.56±1.52 137.13±5.39 P3 30.06±1.17 44.47±1.70 581.52±8.09 P4 20.43±1.06 14.47±1.25 81.38±4.68 P5 15.73±0.99 15.10±1.27 68.63±4.47 P6 13.25±0.95 7.13±1.04 8.96±2.60 P7 29.01±1.16 37.77±1.62 88.31±4.78 P8 31.46±1.19 44.42±1.70 468.59±7.60 P9 28.61±1.16 39.58±1.64 415.23±7.34 P10 25.62±1.13 31.39±1.54 372.28±7.12 Average value 23.14±0.34 27.13±0.46 226.26±1.85 World average 35 30 400 22 4.4.4. The activity concentration results for the sand samples using gamma-ray spectra with HPGe detectors Table 4.8. Average activity concerntration (Bq kg -1 ) in sand samples in Mekong and NamNgeum river Sample Activity co