ASSESSMENT OF THE NATUAL RADIOACTIVITY AND RADIOLOGICAL HAZARDS IN LAO CEMENT SAMPLES

ASSESSMENT OF THE NATUAL RADIOACTIVITY AND RADIOLOGICAL HAZARDS IN LAO CEMENT SAMPLES Abstract The radioactivity concentrations of 226Ra, 232Th and 40K natural radionuclides in Lao Portland cement samples were measured using a gamma-spectrometry with a HPGe detector. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg−1 with a mean value of 41.12 ± 2.44 Bq kg−1 for 226Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg−1 with a mean of 16.60 ± 2.37 Bq kg−1 for 232Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg−1 with a mean of 141.48 ± 4.50 Bq kg−1 for 40K, respectively. The radiological parameters were estimated to assess the potential radiological hazard including radium equivalent activity, total external absorbed dose rate in outdoor air at 1 m above the earth’s surface, the annual effective dose, the gamma and alpha-indices were calculated using the activity concentrations of 226Ra, 232Th and 40K. The results obtained in this study show no significant radiological hazards arising from using Lao Portland cement for building construction. INTRODUCTION Cement is one of the important materials for building in Lao PDR. Because the natural radionuclides (238U, 232Th and their decay progenies and 40K) presence everywhere, therefore the natural radionuclides always more or less exit in Lao cement. In the 238U series, the decay chain segment starting from radium (226Ra) is the most important in terms of radiology and, therefore, reference is often made to 226Ra instead of 238U. The presence of the natural radionuclides in cement will affect the human health so that in many countries, it is necessary to measure the activity concentration of the radionuclides of cement before its utilization for building(1–7). However, detailed information of the activity concentrations of the natural radionuclides of cement produced in Lao PDR is not yet studied and is not available so far. This study is the first work related to the measurement of the natural radioactivity of 238U (226Ra), 232Th and 40K in Lao cement using gamma-ray spectrometric technique and estimation of the gamma dose rate from these radionuclides. The main purposes of this work are: (1) assessment of the natural radionuclides of 226Ra, 232Th and 40K in most popular cements produced by the local cement companies in Lao using a high energy resolution gamma spectrometry, (2) estimation of the radiological parameters such as radium equivalent activity (Raeq), the absorbed dose rate in air (DR), the annual effective dose equivalent (AED), the gamma (Iγ) and alpha (Iα) indices, (3) comparison of the measured activity concentrations of Lao cement samples with the previous published values of some other countries. EXPERIMENTAL METHODS Sampling and Sample Preparation In this research, a total of 19 Portland cement samples produced by four local famous cement companies in Lao PDR were collected. The cement samples, each about 0.4 kg in weight, were dried in a temperature controlled furnace at 110°C for 24 h or more until their weights reach constant to ensure that moisture was completely removed. After moisture removal, these samples were cooled in the moisture-free atmosphere and pulverized into powdered form. The references material and cement samples were packed in a cylindrical container having the following characteristics: external diameter 60 mm, and was filled to height 70 mm. After that, the powdered samples were stored in tight PVC cylindrical containers for 4 weeks to reach secular equilibrium between 226Ra and 222Rn and their decay products. For the activity measurements, the samples were counted for a sufficiently long time in order to obtain a good statistic. The acquisition time is 72 000 s for background, reference and samples respectively. Measurements with an empty sample container under identical conditions were also carried out to determine the ambient background in the laboratory site. Radioactivity Measurement 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 54.7 mm of the ORTEC company, and the relative efficiency 20% and the energy resolution (FWHM) at 1332 keV (60Co) is 1.8 keV, which is connected to a spectroscopy amplifier model 572A (ORTEC) and a computer based PCA-MR 8192 ACCUSPEC multi-channel analyzer. The MAESTRO-32 multi-channel analyzer emulation software was used for data acquisition, storage, display, online and offline analysis of the gamma-spectra. To prevent high background counts due to external radioactive sources, with the intention to reduce the counting time and improve the detection limit, the detector is placed in a low-level Canberra Model 747 lead shield having a thickness of 10 cm. The inner part of the lead shield is covered with copper to reduce KX-rays from the lead. The activity concentration of 40K has been determined directly by its own gamma-ray at 1460.8 keV (10.7%), while the activity concentrations of 226Ra and 232Th have been calculated based on the weighted mean value of their respective decay products in equilibrium. The activity concentration of 226Ra has been determined using the 295.22 keV (18.5%), 351.93 keV (35.6%) gamma-rays from 214Pb and 609.31 keV (45.49%), 768.36 keV (4.89%) 1120.14 keV (0.01%), 1764.43 keV (15.28%) from 214Bi. The activity concentration of 232Th has been determined using the 583.187 keV (85.0%), the 2614.511 keV (99.79%) from 208Tl and 911.12 keV (25.8%) from 228Ac. The value written inside the parentheses following gamma-ray energy indicates the absolute emission probability of the gamma decay. The activity concentrations of each cement sample have been determined by the comparative method using the RGK-1 (activity is 14 000 ± 400 Bq kg−1), RGTh-1 (activity is 3250 ± 90 Bq kg−1) and RGU-1 (activity is 4940 ± 30 Bq kg−1) reference materials, obtained from the International Atomic Energy Agency(8), for which the activity concentration of the interested radionuclides are known. Furthermore, the geometry of the containers of cement samples was identical to that of the reference materials so that the correction due to geometry difference can be ignored. The following equation has been used to calculate the activity concentration of the radionuclides in the cement samples by the comparative method:   As=CsCref×MsMref×GsGref×1−e−0.683ts/T1/2,i1−e−0.693tref/T1/2,i×Aref (1)where As and Aref are the activity concentrations of the cement and reference samples in Bq kg−1; Cs and Cref are the count rates obtained under the corresponding peak of cement sample and reference samples in counts s−1; Ms and Mref are masses of the cement and reference samples in kg; Gs and Gref are the self-absorption correction factors of the cement and reference samples; ts andtref are the measuring live times for the cement and reference samples (s); T1/2,i is the half-life of the radionuclide. The self-absorption correction factors for cement and reference samples have been determined experimentally by transmission method as suggested in detail by the authors in the reference(9). Two point gamma-ray emitter sources of 226Ra and 60Co were used to perform transmission measurements in order to obtain the self-absorption correction factors for the cement and reference samples. The following gamma-rays were used for in these measurements: 241.9 keV, 295.2 keV, 351.9 keV, 609.3 keV, 1274.5 keV and 2204.5 keV emitted by 226Ra; 1173.2 keV and 1332.5 keV emitted by 60Co. We exactly followed the procedure written in this reference and the self-absorption correction factors were obtained at the gamma-ray energies listed above. The self-absorption correction curves for the cement and reference samples were obtained. The self-absorption correction factors at a specific gamma-ray energy of the cement or reference sample can be easily obtained by interpolation method. The mean activity concentrations of 226Ra, 232Th and 40K together with their standard deviations of 19 Portland cement samples are presented in Table 1. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg−1 with a mean value of 41.12 ± 2.44 Bq kg−1 for 226Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg−1 with a mean of 16.60 ± 2.37 Bq kg−1 for 232Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg−1 with a mean of 141.48 ± 4.50 Bq kg−1 for 40K, respectively. The obtained results show that the activity concentrations in the Portland cement under investigation are below the world averages for building materials which are 50, 50 and 500 Bq kg−1 for 226Ra, 232Th and 40K(10). Table 1. The activity concentrations of 226Ra, 232Th, 40K of 19 investigated Lao PDR Portland cement samples. Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  SD means standard deviation. View Large Table 1. The activity concentrations of 226Ra, 232Th, 40K of 19 investigated Lao PDR Portland cement samples. Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  SD means standard deviation. View Large 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 three radionuclides 226Ra, 232Th and 40K. It has been calculated by the following equation:   Raeq=ARa+1.43ATh+0.077AK, (2)where ARa, ATh and Ak are the activity concentrations of 226Ra, 232Th and 40K in Bq kg−1, respectively. The permissible maximum value of the radium equivalent activity is 370 Bq kg−1 which corresponds to the effective dose of 1 mSv for the general public and to the radiation dose rate of 1.5 mGy y−1(10).The calculated values of Raeq of the investigated cement samples are presented in Table 2, which are in the range from 57.31 ± 3.55 to 113.24 ± 4.10 Bq kg−1 with a mean of 71.82 ± 11.47 Bq kg−1. It can be seen that the values of Raeq for all the studied cement samples are lower than the acceptable level of 370 Bq kg−1 for radium equivalent, which corresponds to an annual effective dose of 1 mSv, so that these samples are within the recommended safety limit when they are used as building materials and products. Table 2. Calculated values of radium equivalent activity, absorbed gamma dose rate, annual effective dose, alpha and gamma activity indices, respectively. Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  View Large Table 2. Calculated values of radium equivalent activity, absorbed gamma dose rate, annual effective dose, alpha and gamma activity indices, respectively. Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  View Large Gamma-index (Iγ) and Alpha-index (Iα) The gamma index Iγ was proposed by several investigators for identifying whether the European Commission guidelines about building material usage are met. In this study, the gamma index was calculated as proposed by the European Commission(11) as follows:   Iγ=ARa300+ATh200+AK3000 (3) The case of Iγ ≤ 1 corresponds to an absorbed gamma dose rate less or equal to 1 mSv y−1, while Iγ ≤ 0.5 corresponds to a dose rate criterion of 0.3 mSv y−1(11). Due to radon inhalation originated from buildings material, the alpha index Iα was proposed(10) and it is determined using the following formula:   Iα=ARa200 (4)where ARa is the activity concentration of 226Ra which is assumed in equilibrium with 238U. The recommended upper limit is Iα = 1 which corresponds to the activity concentration 200 Bq kg−1of 226Ra. The cement is safe for use if Iα ≤ 1. The calculated gamma Iγ and alpha Iα indices for the investigated cement samples are listed in Table 2. The values of gamma index Iγ vary from 0.199 ± 0.011 to 0.431 ± 0.011 with a mean value of 0.270 ± 0.011, which is smaller than 0.5. The values of Iα vary from 0.142 ± 0.011 to 0.333 ± 0.014 with a mean value of 0.206 ± 0.012 and all of them are smaller than the recommended upper limit. Absorbed Dose Rate (D) The activity concentrations of 226Ra, 232Th and 40K 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(10):   DR=0.462ARa+0.604ATh+0.0417AK≤80nGy.h−1 (5) The safe threshold value of DR is 80 nGy h−1. For our investigated cement samples, the values of DR were found in the range from 26.74 ± 1.67 nGy h−1 to 54.97 ± 1.88 nGy h−1 with a mean value of 35.28 ± 1.83 nGy h−1 as shown in Table 2. These values are lower than the threshold of the safe absorbed dose rate. The annual effective dose in mSv y−1 was calculated by the following formula(10):   AED(mSv.y−1)=DR(nGy.h−1)×8760(h)×0.8×0.7(Sv.Gy−1)×10−6 (6)where DR is the absorbed dose rate, 0.8 stands for the indoor occupancy coefficient which implying that on average 80% of time is spent indoors, and a value of 0.7 Sv Gy–1 was used for converting from absorbed dose in air to effective dose received by adults.The calculated annual effective dose for the investigated cement samples are listed in Table 2 as well. The values of the annual effective dose range from 0.131 ± 0.019 mSv y−1 to 0.270 ± 0.010 mSv y−1 with a mean of 0.173 ± 0.013 mSv y−1. Table 3 shows a comparison between the activity concentrations of cement in Lao PDR with those from other countries, which are available in the literatures. It is important to said that these values are not representative values for countries mentioned, but are representative of the region from where the samples were collected. Overall, as can be seen from this table, the activity levels of 226Ra, 232Th and 40K vary from one country to another. These variations may come from the differences of the materials that are used in the cement manufacture. Table 3. Comparison of mass activities and radium equivalent activity (Bq kg−1) in cement samples in this work with other countries of the world. Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  Table 3. Comparison of mass activities and radium equivalent activity (Bq kg−1) in cement samples in this work with other countries of the world. Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  CONCLUSIONS This is the first work to investigate the activity concentration of the natural radionuclides of the Portland cement produced by different local cement production company in Lao PDR. The activity concentrations of the natural radionuclides of 226Ra, 232Th and 40K of 19 Lao Portland cement samples were measured for the first time using the gamma-spectrometry with HPGe detector. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg−1 with a mean value of 41.12 ± 2.44 Bq kg−1 for 226Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg−1 with a mean of 16.60 ± 2.37 Bq kg−1 for 232Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg−1 with a mean of 141.48 ± 4.50 Bq kg−1 for 40K, respectively. The radium equivalent activity Raeq, the external absorbed dose rate DR in outdoor air at 1 m above the earth’s surface, the annual effective dose AED, the gamma and alpha-indices were calculated using the activity concentrations of 226Ra, 232Th and 40K. The mean value of the Raeq was 76.41 ± 5.42 Bq kg−1, which is lower than the limit of 370 Bq kg−1 set for building materials. The mean absorbed dose rate DR in air was 35.28 ± 1.83 nGy h−1 and the mean annual effective dose AED was 0.173 ± 0.013 mSv y−1. These values are well below the permissible limits. Finally, the gamma Iγ and alpha Iα indices were estimated with their mean values of 0.270 ± 0.011 and 0.206 ± 0.012, respectively. The obtained values for Lao cement in our work were compared with the same values of cement of some other countries for reference. The results in this study show that Lao Portland cement do not pose a significant radiological hazard when used for building construction. ACKNOWLEDGEMENTS This work was supported by the Institute of Physics, Vietnam Academy of Science and Technology. REFERENCES 1 Trevisi, R., Risica, S., D’Alessandro, M., Paradiso, D. and Nuccetelli, C. Natural radioactivity in building materials in the European Union: a database and an estimate of radiological significance. J. Environ. Radioact.  105, 11– 20 ( 2012). Google Scholar CrossRef Search ADS PubMed  2 Xhixha, X. et al.  . First characterization of natural radioactivity in building materials manufactured in Albania. Radiat. Prot. Dosim.  155, 217– 223 ( 2013). Google Scholar CrossRef Search ADS   3 Flores, O. B., Estrada, A. M., Suares, R. R., Zerquera, J. T. and Perez, A. H. Natural radionuclide content in building materials and gamma dose rate in dwellings in Cuba. J. Environ. Radioact.  99, 1834– 1837 ( 2008). Google Scholar CrossRef Search ADS PubMed  4 Khandaker, M. U., Jojo, P. J., Kassim, H. A. and Amin, Y. M. Radiometric analysis of construction materials using HPGe gamma-ray spectrometry. Radiat. Prot. Dosim.  153, 352– 360 ( 2012). 5 Lee, S. C., Kim, C. K., Lee, D. M. and Kang, H. D. Natural radionuclides contents and radon exhalation rates in building materials used in south Korea. Radiat. Prot. Dosim.  94, 269– 274 ( 2001). Google Scholar CrossRef Search ADS   6 Roy, S., Alam, M. S., Begum, M. and Alam, B. Radioactivity in building materials used in and around Dhaka city. Radiat. Prot. Dosim.  114, 527– 532 ( 2005). Google Scholar CrossRef Search ADS   7 Le, N. S., Nguyen, T. B., Truong, Y., Nguyen, T. N., Nguyen, T. L., Nguyen, V. P., Nguyen, D. T., Nguyen, K. T. and Khoa, T. D. Natural radioactivity in commonly building materials used in Vietnam. 11255 WM 2011 Conference, February 27–March 3, 2011, ( 2011). 8 NEA-OECD. Nuclear Energy Agency. Exposure to radiation from natural radioactivity in building materials. Reported by NEA Group of Expert OECD ( 1979). 9 Cutshall, N. H., Larsen, I. L. and Olsen, C. R. Direct analysis of 210Pb in sediment samples: self-absorption corrections. Nucl. Instrum. Methods  206, 309– 312 ( 1983). Google Scholar CrossRef Search ADS   10 UNSCEAR. Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation  ( New York, USA: United Nations Publications) ( 2000). 11 IAEA. Preparation of gamma-ray spectrometry reference materials RGU-1, RGTh-1 and RGK-1. Report-IAEA/RL/148, Vienna ( 1987). 12 Stoulos, S., Manolopoulou, M. and Papastefanou, C. Assessment of natural radiation exposure and radon exhalation from building materials in Greece. J. Environ. Radioact.  69, 225– 235 ( 2003). Google Scholar CrossRef Search ADS PubMed  13 Damla, N., Cevik, U., Kobya, A. I., Celik, A., Celik, N. and Van Grieken, R. Radiation dose estimation and mass attenuation coefficients of cement samples used in Turkey. J. Hazard. Mater.  176, 644– 649 ( 2010). Google Scholar CrossRef Search ADS PubMed  14 Al-Sulaiti, H. et al.  . Determination of the natural radioactivity in Quatarian building materials using high-resolution gamma-ray spectrometry. Nucl. Instrum. Methods Phys. Res. A  652, 915– 919 ( 2011). Google Scholar CrossRef Search ADS   15 Kpeglo, D. O., Lawluvi, H., Faanu, A., Awudu, A. R., Deatanyah, P., Wotorchi, S. G., Arwui, C. C., Emi-Reynolds, G. and Darko, E. O. Natural radioactivity and its associated radiological hazards in Ghanaian cement. Res. J. Environ. Earth Sci.  3, 161– 167 ( 2011). 16 Amrani, D. and Tahtat, M. Natural radioactivity in Algerian building materials. Appl. Radiat. Isot.  54, 687– 689 ( 2001). Google Scholar CrossRef Search ADS PubMed  17 Hayumbu, P., Xaman, M. B., Luhaba, C. C. H., Munsaje, S. S. and Nuleya, D. Natural radioactivity in Zambian building materials collected from Lusaka. J. Radioanal. Nucl. Chem.  199, 229– 238 ( 1995). Google Scholar CrossRef Search ADS   18 Xinwei, L. Radioactive analysis of cement and its products collected from Shaanxi, China. Health Phys. 88, 84– 86 ( 2005). 19 Malanca, A., Pessina, V., Dallara, G., Luce, C. N. and Gaidol, L. Natural radioactivity in building materials from the Brazilian state of Espirito. Appl. Radiat. Isot.  46, 1387– 1392 ( 1993). Google Scholar CrossRef Search ADS   20 Sharma, N., Singh, J., ChinnaEsakki, S. and Tripathi, R. M. A study of the natural radioactivity and radon exhalation rate in some cements used in India and its radiological significance. J. Radiat. Res. Appl. Sci.  9, 47– 56 ( 2016). Google Scholar CrossRef Search ADS   21 Yu, K. N., Guan, Z. J., Stokes, M. J. and Young, E. C. M. The assessment of the natural radiation dose commited to the Hong Kong people. J. Environ. Radioact.  17, 31– 48 ( 1992). Google Scholar CrossRef Search ADS   22 Ibrahim, N. Natural activities of 238U, 232Th and 40K in building materials. J. Environ. Radioact.  43, 255– 258 ( 1999). Google Scholar CrossRef Search ADS   © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

ASSESSMENT OF THE NATUAL RADIOACTIVITY AND RADIOLOGICAL HAZARDS IN LAO CEMENT SAMPLES

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com
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0144-8420
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Abstract

Abstract The radioactivity concentrations of 226Ra, 232Th and 40K natural radionuclides in Lao Portland cement samples were measured using a gamma-spectrometry with a HPGe detector. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg−1 with a mean value of 41.12 ± 2.44 Bq kg−1 for 226Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg−1 with a mean of 16.60 ± 2.37 Bq kg−1 for 232Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg−1 with a mean of 141.48 ± 4.50 Bq kg−1 for 40K, respectively. The radiological parameters were estimated to assess the potential radiological hazard including radium equivalent activity, total external absorbed dose rate in outdoor air at 1 m above the earth’s surface, the annual effective dose, the gamma and alpha-indices were calculated using the activity concentrations of 226Ra, 232Th and 40K. The results obtained in this study show no significant radiological hazards arising from using Lao Portland cement for building construction. INTRODUCTION Cement is one of the important materials for building in Lao PDR. Because the natural radionuclides (238U, 232Th and their decay progenies and 40K) presence everywhere, therefore the natural radionuclides always more or less exit in Lao cement. In the 238U series, the decay chain segment starting from radium (226Ra) is the most important in terms of radiology and, therefore, reference is often made to 226Ra instead of 238U. The presence of the natural radionuclides in cement will affect the human health so that in many countries, it is necessary to measure the activity concentration of the radionuclides of cement before its utilization for building(1–7). However, detailed information of the activity concentrations of the natural radionuclides of cement produced in Lao PDR is not yet studied and is not available so far. This study is the first work related to the measurement of the natural radioactivity of 238U (226Ra), 232Th and 40K in Lao cement using gamma-ray spectrometric technique and estimation of the gamma dose rate from these radionuclides. The main purposes of this work are: (1) assessment of the natural radionuclides of 226Ra, 232Th and 40K in most popular cements produced by the local cement companies in Lao using a high energy resolution gamma spectrometry, (2) estimation of the radiological parameters such as radium equivalent activity (Raeq), the absorbed dose rate in air (DR), the annual effective dose equivalent (AED), the gamma (Iγ) and alpha (Iα) indices, (3) comparison of the measured activity concentrations of Lao cement samples with the previous published values of some other countries. EXPERIMENTAL METHODS Sampling and Sample Preparation In this research, a total of 19 Portland cement samples produced by four local famous cement companies in Lao PDR were collected. The cement samples, each about 0.4 kg in weight, were dried in a temperature controlled furnace at 110°C for 24 h or more until their weights reach constant to ensure that moisture was completely removed. After moisture removal, these samples were cooled in the moisture-free atmosphere and pulverized into powdered form. The references material and cement samples were packed in a cylindrical container having the following characteristics: external diameter 60 mm, and was filled to height 70 mm. After that, the powdered samples were stored in tight PVC cylindrical containers for 4 weeks to reach secular equilibrium between 226Ra and 222Rn and their decay products. For the activity measurements, the samples were counted for a sufficiently long time in order to obtain a good statistic. The acquisition time is 72 000 s for background, reference and samples respectively. Measurements with an empty sample container under identical conditions were also carried out to determine the ambient background in the laboratory site. Radioactivity Measurement 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 54.7 mm of the ORTEC company, and the relative efficiency 20% and the energy resolution (FWHM) at 1332 keV (60Co) is 1.8 keV, which is connected to a spectroscopy amplifier model 572A (ORTEC) and a computer based PCA-MR 8192 ACCUSPEC multi-channel analyzer. The MAESTRO-32 multi-channel analyzer emulation software was used for data acquisition, storage, display, online and offline analysis of the gamma-spectra. To prevent high background counts due to external radioactive sources, with the intention to reduce the counting time and improve the detection limit, the detector is placed in a low-level Canberra Model 747 lead shield having a thickness of 10 cm. The inner part of the lead shield is covered with copper to reduce KX-rays from the lead. The activity concentration of 40K has been determined directly by its own gamma-ray at 1460.8 keV (10.7%), while the activity concentrations of 226Ra and 232Th have been calculated based on the weighted mean value of their respective decay products in equilibrium. The activity concentration of 226Ra has been determined using the 295.22 keV (18.5%), 351.93 keV (35.6%) gamma-rays from 214Pb and 609.31 keV (45.49%), 768.36 keV (4.89%) 1120.14 keV (0.01%), 1764.43 keV (15.28%) from 214Bi. The activity concentration of 232Th has been determined using the 583.187 keV (85.0%), the 2614.511 keV (99.79%) from 208Tl and 911.12 keV (25.8%) from 228Ac. The value written inside the parentheses following gamma-ray energy indicates the absolute emission probability of the gamma decay. The activity concentrations of each cement sample have been determined by the comparative method using the RGK-1 (activity is 14 000 ± 400 Bq kg−1), RGTh-1 (activity is 3250 ± 90 Bq kg−1) and RGU-1 (activity is 4940 ± 30 Bq kg−1) reference materials, obtained from the International Atomic Energy Agency(8), for which the activity concentration of the interested radionuclides are known. Furthermore, the geometry of the containers of cement samples was identical to that of the reference materials so that the correction due to geometry difference can be ignored. The following equation has been used to calculate the activity concentration of the radionuclides in the cement samples by the comparative method:   As=CsCref×MsMref×GsGref×1−e−0.683ts/T1/2,i1−e−0.693tref/T1/2,i×Aref (1)where As and Aref are the activity concentrations of the cement and reference samples in Bq kg−1; Cs and Cref are the count rates obtained under the corresponding peak of cement sample and reference samples in counts s−1; Ms and Mref are masses of the cement and reference samples in kg; Gs and Gref are the self-absorption correction factors of the cement and reference samples; ts andtref are the measuring live times for the cement and reference samples (s); T1/2,i is the half-life of the radionuclide. The self-absorption correction factors for cement and reference samples have been determined experimentally by transmission method as suggested in detail by the authors in the reference(9). Two point gamma-ray emitter sources of 226Ra and 60Co were used to perform transmission measurements in order to obtain the self-absorption correction factors for the cement and reference samples. The following gamma-rays were used for in these measurements: 241.9 keV, 295.2 keV, 351.9 keV, 609.3 keV, 1274.5 keV and 2204.5 keV emitted by 226Ra; 1173.2 keV and 1332.5 keV emitted by 60Co. We exactly followed the procedure written in this reference and the self-absorption correction factors were obtained at the gamma-ray energies listed above. The self-absorption correction curves for the cement and reference samples were obtained. The self-absorption correction factors at a specific gamma-ray energy of the cement or reference sample can be easily obtained by interpolation method. The mean activity concentrations of 226Ra, 232Th and 40K together with their standard deviations of 19 Portland cement samples are presented in Table 1. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg−1 with a mean value of 41.12 ± 2.44 Bq kg−1 for 226Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg−1 with a mean of 16.60 ± 2.37 Bq kg−1 for 232Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg−1 with a mean of 141.48 ± 4.50 Bq kg−1 for 40K, respectively. The obtained results show that the activity concentrations in the Portland cement under investigation are below the world averages for building materials which are 50, 50 and 500 Bq kg−1 for 226Ra, 232Th and 40K(10). Table 1. The activity concentrations of 226Ra, 232Th, 40K of 19 investigated Lao PDR Portland cement samples. Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  SD means standard deviation. View Large Table 1. The activity concentrations of 226Ra, 232Th, 40K of 19 investigated Lao PDR Portland cement samples. Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  Sample  Activity concentration ± SD (Bq kg−1)  226Ra  232Th  40K  S1  39.58 ± 2.41  10.23 ± 2.13  166.26 ± 4.19  S2  44.79 ± 2.49  44.01 ± 2.45  184.64 ± 4.64  S3  44.14 ± 2.48  11.40 ± 2.18  192.62 ± 4.32  S4  44.47 ± 2.48  9.67 ± 2.10  178.75 ± 4.22  S5  44.15 ± 2.49  10.71 ± 2.33  183.51 ± 4.27  S6  38.31 ± 2.38  9.05 ± 2.06  156.01 ± 4.10  S7  43.36 ± 2.47  10.92 ± 2.16  181.42 ± 4.28  S8  32.61 ± 2.29  22.30 ± 2.62  190.83 ± 4.74  S9  31.12 ± 2.25  22.37 ± 2.62  189.09 ± 4.73  S10  31.37 ± 2.27  21.62 ± 2.60  187.57 ± 4.69  S11  32.04 ± 2.28  22.75 ± 2.63  196.74 ± 4.75  S12  62.62 ± 2.78  8.36 ± 2.08  50.74 ± 4.35  S13  57.27 ± 2.72  7.85 ± 2.05  49.18 ± 4.27  S14  43.62 ± 2.40  7.25 ± 2.00  52.90 ± 4.01  S15  66.50 ± 2.83  9.37 ± 2.14  51.90 ± 4.47  S16  31.99 ± 2.32  21.54 ± 2.68  163.19 ± 4.83  S17  30.19 ± 2.29  21.49 ± 2.67  161.78 ± 4.81  S18  34.73 ± 2.37  23.12 ± 2.73  153.90 ± 4.92  S19  28.32 ± 2.23  21.33 ± 2.68  163.22 ± 4.78  Min  28.32 ± 2.23  7.25 ± 2.00  49.19 ± 4.27  Max  66.50 ± 2.83  44.01 ± 2.45  196.74 ± 4.75  Mean ± SD  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  SD means standard deviation. View Large 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 three radionuclides 226Ra, 232Th and 40K. It has been calculated by the following equation:   Raeq=ARa+1.43ATh+0.077AK, (2)where ARa, ATh and Ak are the activity concentrations of 226Ra, 232Th and 40K in Bq kg−1, respectively. The permissible maximum value of the radium equivalent activity is 370 Bq kg−1 which corresponds to the effective dose of 1 mSv for the general public and to the radiation dose rate of 1.5 mGy y−1(10).The calculated values of Raeq of the investigated cement samples are presented in Table 2, which are in the range from 57.31 ± 3.55 to 113.24 ± 4.10 Bq kg−1 with a mean of 71.82 ± 11.47 Bq kg−1. It can be seen that the values of Raeq for all the studied cement samples are lower than the acceptable level of 370 Bq kg−1 for radium equivalent, which corresponds to an annual effective dose of 1 mSv, so that these samples are within the recommended safety limit when they are used as building materials and products. Table 2. Calculated values of radium equivalent activity, absorbed gamma dose rate, annual effective dose, alpha and gamma activity indices, respectively. Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  View Large Table 2. Calculated values of radium equivalent activity, absorbed gamma dose rate, annual effective dose, alpha and gamma activity indices, respectively. Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  Sample  Raeq (Bq kg−1)  DR (nGy h−1)  AED (mSv y−1)  Iα  Iγ  S1  67.01 ± 5.05  31.40 ± 1.71  0.154 ± 0.015  0.198 ± 0.012  0.239 ± 0.011  S2  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.224 ± 0.012  0.431 ± 0.011  S3  75.27 ± 5.19  35.31 ± 1.75  0.173 ± 0.013  0.221 ± 0.012  0.268 ± 0.011  S4  72.08 ± 5.07  33.84 ± 1.72  0.166 ± 0.016  0.222 ± 0.012  0.256 ± 0.011  S5  73.59 ± 5.30  34.52 ± 1.83  0.169 ± 0.015  0.221 ± 0.012  0.262 ± 0.011  S6  63.27 ± 4.93  29.67 ± 1.67  0.146 ± 0.018  0.192 ± 0.012  0.225 ± 0.011  S7  72.95 ± 5.15  34.19 ± 1.74  0.168 ± 0.014  0.217 ± 0.012  0.260 ± 0.011  S8  79.20 ± 5.71  36.49 ± 1.91  0.179 ± 0.013  0.163 ± 0.011  0.284 ± 0.011  S9  77.68 ± 5.69  35.77 ± 1.90  0.175 ± 0.013  0.156 ± 0.011  0.279 ± 0.011  S10  76.73 ± 5.66  35.37 ± 1.90  0.174 ± 0.013  0.157 ± 0.011  0.275 ± 0.011  S11  79.73 ± 5.72  36.75 ± 1.92  0.180 ± 0.012  0.160 ± 0.011  0.286 ± 0.011  S12  78.49 ± 5.27  36.10 ± 1.81  0.177 ± 0.013  0.313 ± 0.014  0.267 ± 0.012  S13  72.29 ± 5.18  33.21 ± 1.77  0.163 ± 0.015  0.286 ± 0.014  0.246 ± 0.012  S14  58.07 ± 4.84  26.74 ± 1.65  0.131 ± 0.019  0.218 ± 0.012  0.199 ± 0.011  S15  83.89 ± 5.41  38.55 ± 1.85  0.189 ± 0.012  0.333 ± 0.014  0.286 ± 0.011  S16  75.36 ± 5.82  34.59 ± 1.95  0.170 ± 0.013  0.160 ± 0.012  0.269 ± 0.011  S17  73.39 ± 5.79  33.67 ± 1.94  0.165 ± 0.014  0.151 ± 0.011  0.262 ± 0.011  S18  79.64 ± 5.93  36.43 ± 1.99  0.179 ± 0.013  0.174 ± 0.012  0.283 ± 0.011  S19  71.40 ± 5.76  32.77 ± 1.93  0.161 ± 0.014  0.142 ± 0.011  0.255 ± 0.011  min  58.07 ± 4.84  26.74 ± 1.67  0.131 ± 0.019  0.142 ± 0.011  0.199 ± 0.011  max  121.95 ± 5.59  54.97 ± 1.88  0.270 ± 0.010  0.333 ± 0.014  0.431 ± 0.011  Mean ± SD  76.41 ± 5.42  35.28 ± 1.83  0.173 ± 0.013  0.206 ± 0.012  0.270 ± 0.011  View Large Gamma-index (Iγ) and Alpha-index (Iα) The gamma index Iγ was proposed by several investigators for identifying whether the European Commission guidelines about building material usage are met. In this study, the gamma index was calculated as proposed by the European Commission(11) as follows:   Iγ=ARa300+ATh200+AK3000 (3) The case of Iγ ≤ 1 corresponds to an absorbed gamma dose rate less or equal to 1 mSv y−1, while Iγ ≤ 0.5 corresponds to a dose rate criterion of 0.3 mSv y−1(11). Due to radon inhalation originated from buildings material, the alpha index Iα was proposed(10) and it is determined using the following formula:   Iα=ARa200 (4)where ARa is the activity concentration of 226Ra which is assumed in equilibrium with 238U. The recommended upper limit is Iα = 1 which corresponds to the activity concentration 200 Bq kg−1of 226Ra. The cement is safe for use if Iα ≤ 1. The calculated gamma Iγ and alpha Iα indices for the investigated cement samples are listed in Table 2. The values of gamma index Iγ vary from 0.199 ± 0.011 to 0.431 ± 0.011 with a mean value of 0.270 ± 0.011, which is smaller than 0.5. The values of Iα vary from 0.142 ± 0.011 to 0.333 ± 0.014 with a mean value of 0.206 ± 0.012 and all of them are smaller than the recommended upper limit. Absorbed Dose Rate (D) The activity concentrations of 226Ra, 232Th and 40K 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(10):   DR=0.462ARa+0.604ATh+0.0417AK≤80nGy.h−1 (5) The safe threshold value of DR is 80 nGy h−1. For our investigated cement samples, the values of DR were found in the range from 26.74 ± 1.67 nGy h−1 to 54.97 ± 1.88 nGy h−1 with a mean value of 35.28 ± 1.83 nGy h−1 as shown in Table 2. These values are lower than the threshold of the safe absorbed dose rate. The annual effective dose in mSv y−1 was calculated by the following formula(10):   AED(mSv.y−1)=DR(nGy.h−1)×8760(h)×0.8×0.7(Sv.Gy−1)×10−6 (6)where DR is the absorbed dose rate, 0.8 stands for the indoor occupancy coefficient which implying that on average 80% of time is spent indoors, and a value of 0.7 Sv Gy–1 was used for converting from absorbed dose in air to effective dose received by adults.The calculated annual effective dose for the investigated cement samples are listed in Table 2 as well. The values of the annual effective dose range from 0.131 ± 0.019 mSv y−1 to 0.270 ± 0.010 mSv y−1 with a mean of 0.173 ± 0.013 mSv y−1. Table 3 shows a comparison between the activity concentrations of cement in Lao PDR with those from other countries, which are available in the literatures. It is important to said that these values are not representative values for countries mentioned, but are representative of the region from where the samples were collected. Overall, as can be seen from this table, the activity levels of 226Ra, 232Th and 40K vary from one country to another. These variations may come from the differences of the materials that are used in the cement manufacture. Table 3. Comparison of mass activities and radium equivalent activity (Bq kg−1) in cement samples in this work with other countries of the world. Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  Table 3. Comparison of mass activities and radium equivalent activity (Bq kg−1) in cement samples in this work with other countries of the world. Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  Country  Activity concentration (Bq kg−1)  Reference  226Ra  232Th  40K  EU  45  31  216  Trevisi et al.(1)  UK  22  18  155  NEA-OECD(8)  Sweden  55  47  241  NEA-OECD(8)  Norway  30  18  241  NEA-OECD(8)  Finland  44  26  241  NEA-OECD(8)  Greece  20 ± 5  13 ± 3  247 ± 68  Stoulos et al.(12)  Albania  55.0 ± 5.8  17.0 ± 3.3  179.7 ± 48.9  Xhixha et al.(2)  Turkey  52  40  324  Damla et al.(13)  Egypt  34 ± 4  12 ± 2  60 ± 13  Mahmoud(14)  Nigeria  43.8  21.5  71.7  Ademola(15)  Algeria  41 ± 7  27 ± 3  422 ± 3  Amrani et al.(16)  Zambia  23 ± 2  32 ± 3  134 ± 13  Hayumbu et al.(17)  Ghana  35.94  25.44  233.0  Kpeglo et al.(18)  Qatar  23.4 ± 0.6  12.2 ± 0.2  158.8 ± 4.3  Al-Sulaiti et al.(14)  Brazil  61.7  58.5  564  Malanca et al.(19)  Cuba  23 ± 7  11 ± 3  467 ± 85  Flores et al.(3)  Pakistan  37 ± 3  28 ± 3  200 ± 14  Khandaker et al.(4)  South Korea  34.5 ± 1.7  19.4 ± 1.5  241 ± 6.7  Lee et al.(5)  China  56.50  36.50  173.2  Xinwei(20)  Hong Kong  19.2  18.9  127  Yu et al.(21)  Malaysia  51 ± 1.0  23 ± 1.0  832 ± 69  Ibrahim(22)  India  35.8 ± 12.3  33.2 ± 13.6  199.1 ± 26.5  Sharma et al.(10)  Bangladesh  61.1 ± 0.8  79.9 ± 1.2  1132 ± 17.3  Roy et al.(6)  Vietnam  39.86 ± 17.43  25.46 ± 4.69  243.5 ± 62.2  Le et al.(7)  Lao PDR  41.12 ± 2.44  16.60 ± 2.37  141.48 ± 4.50  This work  CONCLUSIONS This is the first work to investigate the activity concentration of the natural radionuclides of the Portland cement produced by different local cement production company in Lao PDR. The activity concentrations of the natural radionuclides of 226Ra, 232Th and 40K of 19 Lao Portland cement samples were measured for the first time using the gamma-spectrometry with HPGe detector. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg−1 with a mean value of 41.12 ± 2.44 Bq kg−1 for 226Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg−1 with a mean of 16.60 ± 2.37 Bq kg−1 for 232Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg−1 with a mean of 141.48 ± 4.50 Bq kg−1 for 40K, respectively. The radium equivalent activity Raeq, the external absorbed dose rate DR in outdoor air at 1 m above the earth’s surface, the annual effective dose AED, the gamma and alpha-indices were calculated using the activity concentrations of 226Ra, 232Th and 40K. The mean value of the Raeq was 76.41 ± 5.42 Bq kg−1, which is lower than the limit of 370 Bq kg−1 set for building materials. The mean absorbed dose rate DR in air was 35.28 ± 1.83 nGy h−1 and the mean annual effective dose AED was 0.173 ± 0.013 mSv y−1. These values are well below the permissible limits. Finally, the gamma Iγ and alpha Iα indices were estimated with their mean values of 0.270 ± 0.011 and 0.206 ± 0.012, respectively. The obtained values for Lao cement in our work were compared with the same values of cement of some other countries for reference. The results in this study show that Lao Portland cement do not pose a significant radiological hazard when used for building construction. ACKNOWLEDGEMENTS This work was supported by the Institute of Physics, Vietnam Academy of Science and Technology. REFERENCES 1 Trevisi, R., Risica, S., D’Alessandro, M., Paradiso, D. and Nuccetelli, C. Natural radioactivity in building materials in the European Union: a database and an estimate of radiological significance. J. Environ. Radioact.  105, 11– 20 ( 2012). Google Scholar CrossRef Search ADS PubMed  2 Xhixha, X. et al.  . First characterization of natural radioactivity in building materials manufactured in Albania. Radiat. Prot. Dosim.  155, 217– 223 ( 2013). Google Scholar CrossRef Search ADS   3 Flores, O. B., Estrada, A. M., Suares, R. R., Zerquera, J. T. and Perez, A. H. Natural radionuclide content in building materials and gamma dose rate in dwellings in Cuba. J. Environ. Radioact.  99, 1834– 1837 ( 2008). Google Scholar CrossRef Search ADS PubMed  4 Khandaker, M. U., Jojo, P. J., Kassim, H. A. and Amin, Y. M. Radiometric analysis of construction materials using HPGe gamma-ray spectrometry. Radiat. Prot. Dosim.  153, 352– 360 ( 2012). 5 Lee, S. C., Kim, C. K., Lee, D. M. and Kang, H. D. Natural radionuclides contents and radon exhalation rates in building materials used in south Korea. Radiat. Prot. Dosim.  94, 269– 274 ( 2001). Google Scholar CrossRef Search ADS   6 Roy, S., Alam, M. S., Begum, M. and Alam, B. Radioactivity in building materials used in and around Dhaka city. Radiat. Prot. Dosim.  114, 527– 532 ( 2005). Google Scholar CrossRef Search ADS   7 Le, N. S., Nguyen, T. B., Truong, Y., Nguyen, T. N., Nguyen, T. L., Nguyen, V. P., Nguyen, D. T., Nguyen, K. T. and Khoa, T. D. Natural radioactivity in commonly building materials used in Vietnam. 11255 WM 2011 Conference, February 27–March 3, 2011, ( 2011). 8 NEA-OECD. Nuclear Energy Agency. Exposure to radiation from natural radioactivity in building materials. Reported by NEA Group of Expert OECD ( 1979). 9 Cutshall, N. H., Larsen, I. L. and Olsen, C. R. Direct analysis of 210Pb in sediment samples: self-absorption corrections. Nucl. Instrum. Methods  206, 309– 312 ( 1983). Google Scholar CrossRef Search ADS   10 UNSCEAR. Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation  ( New York, USA: United Nations Publications) ( 2000). 11 IAEA. Preparation of gamma-ray spectrometry reference materials RGU-1, RGTh-1 and RGK-1. Report-IAEA/RL/148, Vienna ( 1987). 12 Stoulos, S., Manolopoulou, M. and Papastefanou, C. Assessment of natural radiation exposure and radon exhalation from building materials in Greece. J. Environ. Radioact.  69, 225– 235 ( 2003). Google Scholar CrossRef Search ADS PubMed  13 Damla, N., Cevik, U., Kobya, A. I., Celik, A., Celik, N. and Van Grieken, R. Radiation dose estimation and mass attenuation coefficients of cement samples used in Turkey. J. Hazard. Mater.  176, 644– 649 ( 2010). Google Scholar CrossRef Search ADS PubMed  14 Al-Sulaiti, H. et al.  . Determination of the natural radioactivity in Quatarian building materials using high-resolution gamma-ray spectrometry. Nucl. Instrum. Methods Phys. Res. A  652, 915– 919 ( 2011). Google Scholar CrossRef Search ADS   15 Kpeglo, D. O., Lawluvi, H., Faanu, A., Awudu, A. R., Deatanyah, P., Wotorchi, S. G., Arwui, C. C., Emi-Reynolds, G. and Darko, E. O. Natural radioactivity and its associated radiological hazards in Ghanaian cement. Res. J. Environ. Earth Sci.  3, 161– 167 ( 2011). 16 Amrani, D. and Tahtat, M. Natural radioactivity in Algerian building materials. Appl. Radiat. Isot.  54, 687– 689 ( 2001). Google Scholar CrossRef Search ADS PubMed  17 Hayumbu, P., Xaman, M. B., Luhaba, C. C. H., Munsaje, S. S. and Nuleya, D. Natural radioactivity in Zambian building materials collected from Lusaka. J. Radioanal. Nucl. Chem.  199, 229– 238 ( 1995). Google Scholar CrossRef Search ADS   18 Xinwei, L. Radioactive analysis of cement and its products collected from Shaanxi, China. Health Phys. 88, 84– 86 ( 2005). 19 Malanca, A., Pessina, V., Dallara, G., Luce, C. N. and Gaidol, L. Natural radioactivity in building materials from the Brazilian state of Espirito. Appl. Radiat. Isot.  46, 1387– 1392 ( 1993). Google Scholar CrossRef Search ADS   20 Sharma, N., Singh, J., ChinnaEsakki, S. and Tripathi, R. M. A study of the natural radioactivity and radon exhalation rate in some cements used in India and its radiological significance. J. Radiat. Res. Appl. Sci.  9, 47– 56 ( 2016). Google Scholar CrossRef Search ADS   21 Yu, K. N., Guan, Z. J., Stokes, M. J. and Young, E. C. M. The assessment of the natural radiation dose commited to the Hong Kong people. J. Environ. Radioact.  17, 31– 48 ( 1992). Google Scholar CrossRef Search ADS   22 Ibrahim, N. Natural activities of 238U, 232Th and 40K in building materials. J. Environ. Radioact.  43, 255– 258 ( 1999). Google Scholar CrossRef Search ADS   © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com

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Radiation Protection DosimetryOxford University Press

Published: Feb 3, 2018

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