This study measured the terrestrial gamma radiation and associated dose rates from primordial radionuclides 238U, 40K and 232Th in sixty soil samples collected from north, west, east and south of Ewekoro cement factory

premises, Owowo village situated adjacent the factory and Covenant University, Ogun State using gamma ray spectrometry method. In order to estimate the radiological hazard index of the natural radioactivity, the gamma absorbed dose rate, annual effective dose and hazard indices were estimated. The measured activity

concentrations of radionuclides in Ewekoro cement factory soils [238U {1.60±1.60 Bqkg−1 (east) - 2.56±0.08 Bqkg−1 (north)}, 232Th {44.78±1.83 Bqkg−1 (east) - 56.62±1.96 Bqkg−1 (north)}, 40K {261.54±12.67 Bqkg−1

(south) - 342.08±14.17 Bqkg−1 (east)}] and Owowo village [238U {1.78±0.09 Bqkg−1 (east) - 2.62±0.08 Bqkg−1 (north)}, 232Th {50.07±1.93 Bqkg−1 (west) - 61.69±1.89 Bqkg−1 (north)}, 40K {244.11±13.38 Bqkg−1 (north) - 296.40±14.90 Bqkg−1 (south)}] soils are higher than that of Covenant University soils [238U {0.62±0.07 Bqkg−1 (south) - 1.07±0.06 Bqkg−1 (north)}, 232Th {30.23±1.87 Bqkg−1 (south) - 38.87±1.78 Bqkg−1 (east)}, 40K { 243.35±12.57 Bqkg−1 (south) - 301.15±13.55 Bqkg−1 (north)}]. The radiation hazard indices estimated were less than unity, the mean absorbed dose and annual effective dose rates are 40.88 nGyr-1 and 0.05 mSv respectively. The study found that the activity concentrations and radiological hazard index from samples from Ewekoro and the neighbouhood are consistently higher than those from Covenant University however, the values are less than the recommended safe levels

Achuka, J.A

Akinyemi, M. L.

Usikalu, M.R.

English

Covenant University Repository

 Available online at www.sciencedirect.com  IERI Procedia 00 (2014) 000–000  2014 International Conference on Environment Systems Science and Engineering Investigation of gamma radiation levels in soil samples collected from some locations in Ogun State, Nigeria Usikalu M.R.*, Akinyemi M.L. and Achuka J.A Department of Physics, Covenant University, P.M.B.1023, Ota, Ogun State, Nigeria   Abstract This study measured the terrestrial gamma radiation and associated dose rates from primordial radionuclides 238U, 40K and 232Th in sixty soil samples collected from north, west, east and south of Ewekoro cement factory premises, Owowo village situated adjacent the factory and Covenant University, Ogun State using gamma ray spectrometry method. In order to estimate the radiological hazard index of the natural radioactivity, the gamma absorbed dose rate, annual effective dose and hazard indices were estimated. The measured activity concentrations of radionuclides in Ewekoro cement factory soils [238U {1.60±1.60 Bqkg−1 (east) - 2.56±0.08 Bqkg−1 (north)}, 232Th {44.78±1.83 Bqkg−1 (east) - 56.62±1.96 Bqkg−1 (north)}, 40K {261.54±12.67 Bqkg−1 (south) - 342.08±14.17 Bqkg−1 (east)}] and Owowo village [238U {1.78±0.09 Bqkg−1 (east) - 2.62±0.08 Bqkg−1 (north)}, 232Th {50.07±1.93 Bqkg−1 (west) - 61.69±1.89 Bqkg−1 (north)},  40K {244.11±13.38 Bqkg−1 (north) - 296.40±14.90 Bqkg−1 (south)}] soils are higher than that of Covenant University soils [238U {0.62±0.07 Bqkg−1 (south) - 1.07±0.06 Bqkg−1 (north)}, 232Th {30.23±1.87 Bqkg−1 (south) - 38.87±1.78 Bqkg−1 (east)}, 40K { 243.35±12.57 Bqkg−1 (south) - 301.15±13.55 Bqkg−1 (north)}].  The radiation hazard indices estimated were less than unity, the mean absorbed dose and annual effective dose rates are 40.88 nGyr-1 and 0.05 mSv respectively. The study found that the activity concentrations and radiological hazard index from samples from Ewekoro and the neighbouhood are consistently higher than those from Covenant University however, the values are less than the recommended safe levels.     © 2014 Usikalu M.R.*, Akinyemi M.L. and Achuka J.A  Published by Elsevier B.V. Selection and peer review under responsibility of Information Engineering Research Institute  Keywords: Primordial radionuclides, activity concentrations, soils, ewekoro cement factory, Covenant University  1.  Introduction Natural radioactivity arises mainly from the primordial radionuclides, such as 40K, and the radionuclides from 238U and 232Th series and their decay products, which are present at trace levels in all ground formations [1]. Human population is exposed to radiation from these radionuclides directly, as a result of external exposure, or through incorporation of these radionuclides into the body through inhalation or ingestion [2]. Estimation 2 Usikalu et al./ IERI Procedia 00 (2014) 000–000 of the radiation dose distribution is important in assessing the health risk to a population and serve as the reference in documenting changes to environmental radioactivity in soil due to anthropogenic activities. Since these radionuclides are not uniformly distributed, the knowledge of their distribution in soil and rock play an important role in radiation protection and measurement [3]. Cement is produced majorly from limestone and some small quantities of other materials such as clay, shale ash and ion oxide. They also contain some elements like gypsum, which contains silicate and aluminates that have ionization tendency [4]. Limestone which is the main constituent in cement is largely abundant in the earth crust (the residence of primordial radionuclides). Therefore, the materials taken from the Earth’s crust and used in the construction of dwellings are one of the sources of (indoor) external exposure [5]. A crucial process in cement production is the quarry process. Research has shown that this process increases the activity concentration of radionuclides in the production environment [6, 7]. However, there are dearths of information on the radioactivity measurement of the effect of Cement manufacturing company in Ewekoro to the human population. Therefore, this work measures the specific activity of 40K, 234Th, and 238U and estimates the radiological hazard associated with them in soil samples obtained in Ewekoro cement plant, Owowo a neigbouring community and Covenant University Ota all in Ogun State.   1.2  Materials and Methods Sample Collection and Preparation Soil Samples were collected from Ewekoro cement plant cited in Itori local government located at 6o56’N and 3o13’E Nigeria Owowo village situated adjacent to the cement factory and Covenant university located in Ota 6o41’N and 3o41’E the local government headquarter of Ado-odo Ota Ogun State, Southwestern Nigeria. The locations are within the Eastern Dahomey Basin of Nigeria. A total of 60 soil samples were collected from north, south, west and east of each study area. The study area was divided into three zones: Ewekoro cement factory, neighborhood of the factory site and Covenant University Ota. An area of 3 ×3 m2 was marked at every sampling location, and the top 0.5-cm surface layer along with vegetation was removed prior to taking the sample. About 2 kg of soil sample comprising five cores was collected from selected area using coring device. The depth of each sample was 5 cm, having a diameter of 10 cm. Such five samples were thoroughly mixed to prepare one representative sample of the sampling site. The samples were dried at the ambient temperature of about 30oC for many days until a constant weight was attained indicating the lowest water content. The dried samples were pulverized and 240 g of each was then filled into an empty cylindrical plastic container of uniform size (9 cm height and 7 cm diameter) and sealed for about 30 days to allow 238U and 232Th and their progenies to reach secular equilibrium before radiometric analysis was carried out.   1.3  Gamma Spectrometry Analysis  The samples were counted for 36,000 seconds to achieve minimum counting error in a low-level gamma counting spectrometer comprising a 7.6 cm x 7.6 cm NaI (Tl) detector (Model No 802-series) by Canberra Inc., which is coupled to a Canberra Series 10 plus Multichannel Analyzer (MCA) (Model No 1104) through a preamplifier base. The detector has a resolution of about 8% at 0.662 MeV of 137Cs which is capable of distinguishing the gamma ray energies used for the measurements. The photopeak at 1.460 MeV was used for the measurement of 40K while those at 1.760 MeV peak from 214Bi and 2.614 MeV from 208Tl were used for the measurement of 226Ra and 232Th, respectively. The detector is coupled to a set of amplifier, Analog-to-Digital Converter (ADC) that bring out an output through a Canberra S100 Multi-Channel Analyzer (MCA) using a spectrum analysis program SAMPO 90. The detector was quoted at 25% efficiency and calibration was achieved using an IAEA-375 Reference soil supply by the International Atomic Energy Agency (IAEA) [8]. Each sample was counted for. For quality assurance the gamma ray spectroscopy analysis adopted in this work was used by several researchers [9, 10, 11, and 12]. The mean specific activity was computed using equation (1)  Usikalu et al./ IERI Procedia  00 (2014) 000–000 3 ξγ ... PtMAAcsnetc =        1 where Ac is the activity concentration of radionuclide (Bq kg-1), Anet is the net area under the peak of radionuclide, Ms is the mass of the sample (kg), tc is the counting time (s), Pγ is the emission probability and ξ is the efficiency of the detector.     1.4 Results and Discussion Activity Concentration  The specific activity of the natural radionuclides (238U, 232Th, and 40K) in the samples was presented in Table 1. 232Th activity in the soil samples is distinctly higher than that of 238U and it ranges between 30.23 Bqkg−1 (NU2) and 61.69 Bqkg−1 (NN1) with a mean activity of 46.91±1.87 Bqkg−1. 238U concentration in the soil samples ranges between 0.62 Bqkg−1 (NU2) and 2.61 Bqkg−1 (NN1) with a mean activity of 1.67±0.35 Bqkg−1 and was found to be lesser than that of both 232Th and 40K. The activity of 40K in all the samples was found higher when compared to that of 232Th and 238U in all sampling locations studied, it ranges between 243.35 Bqkg−1 (NU3) and 342.08 Bqkg−1 (NE3) with a mean activity of 280.52±14.04 Bqkg−1. In order to compare the activity concentrations of three natural radionuclides in soil samples, correlations between them was plotted Figure 2(I-III) presents correlations between the activity concentration of 238U and 232Th, 238U and 40K, and 232Th and 40K respectively, with a trend line drawn among the data points using regression technique. In all the three cases, the regression was found to be linear and positive. The correlation coefficient between 238U and 232Th was high (0.96) whereas correlation between 238U and 40K and 232Th and 40K was very low. It is not surprising, since 238U and 232Th come from natural decay series 238U and 232Th whereas 40K, although a naturally occurring radionuclide, is not part of any such decay series. However, a positive correlation may still be attributed to the property of the soil in retaining these radionuclides under varying weather conditions. It was also observed from Table 1 that the mean value of 40K was the highest and that of 238U was the lowest in all the study area. The spatial distribution of the radionuclides across the three locations under study revealed that the concentration of 40 K and 234Th was highest at the neighboring settlement while Covenant University has the lowest concentration of 238U and 234Th. The result also revealed that highest concentrations of the three radionuclides were consecutively obtained in the samples from Ewekoro cement and neighbourhoods by factor 23% of 238U, 49% of 232Th and 71% of 40K compared to Covenant University that is about 12 km to the cement factory which suggest that the cement factory increased radiation level of the population within the vicinity. The results obtained in this study are comparable to worldwide average concentration of these radionuclides in soils reported [13].  1.5 Gamma Absorbed Dose Rates and Estimation of Hazard Indices   The absorbed dose of the naturally occurring radionuclide from the samples was calculated using equation 2 (UNSCEAR, 2000). D (nGyh-1) = 0.604Cth + 0.462Cu + 0.042Ck       (2) Annual effective dose (Sv y-1) = D (nGyh-1) x (8760 h y-1) x 0.2 x 0.7(SvGy-1)   (3) where, Cth, Cu, Ck are the activity concentrations (Bq kg-1) of 232Th, 238U and 40K, respectively in the soil sample and 0.604, 0.462 and 0.042 (nGy h-1 per Bq kg-1) are the activity concentration-to-dose conversion factors. The outdoor gamma absorbed doses in air ranging between 28.77 nGy.h−1 and 48.38 nGy.h−1 with a mean of 40.88 nGy.h−1 for the study area, which is less than the world average value of 60 nGyh-1. The differences are considered to be due to the geological settings and the influence of the cement manufacturing in the area, which vary from one place to another and from one locality to another in the same zone. The mean 4 Usikalu et al./ IERI Procedia 00 (2014) 000–000 dose rate is important for determining radiation detriment to the population as a whole, but some members of the population may receive higher doses due to high concentration of radionuclides. A common feature in any environmental radiation measurements is the considerable variation in soil radioactivity with location depending on soil physiochemical parameters. The largest contribution from natural radionuclides in the study area soil samples to the absorbed doses in air is due to 232Th. In order to estimate the annual effective dose, the conversion coefficient from absorbed dose in air to effective dose, the indoor occupancy factor of 20% base on the average, spent  of their time outdoors, using the dose rate data obtained from the concentration values of natural radionuclides in soil and adopting the conversion factor of 0.7 Sv/Gy  was substituted into  equation 3 [13]. The calculated values of annual effective dose range from 0.035 to 0.06 mSv, with a mean value of 0.05 mSv, which is lower than the world average of 0.48 mSv [13].   Radiation hazards due to naturally occurring radionuclides 238U, 232Th, and 40K may be indoor or outdoor depending upon the location of a receptor indoor (inside a dwelling) or outdoor (outside a dwelling). The radiation hazards are defined in terms of indoor or outdoor radiation hazard index and are denoted by Hin and Hout, respectively. They were calculated using equation (4) and (5) respectively [14].  Hin = CU/370 + CTh/185 + CK/4810 ≤ 1                        (4) Hex = CU/370 + CTh/259 + CK/4810 ≤ 1       (5) The indoor hazard index was calculated to determine the radiation hazard to respiratory organs due to 222Rn and its other short-lived decay products. The values of Hout and Hin calculated from the measured activity concentrations of 238U, 232Th, and 40K. The results indicated that indoor radiation hazard index was greater than outdoor radiation hazard index at every sampling site. The indoor radiation hazard index  (Hin) range from 0.17 to 0.30 with a mean value of 0.25, whereas the outdoor radiation hazard index (Hout) range between 0.17 to 0.30 with a mean value of 0.24. The mean values of the indoor and the outdoor radiation hazard indices were found to be less than the critical value of unity. This indicated that the soil of study area was free from the radiation hazards. The value of Hout must be lower than unity to keep the radiation hazard insignificant. These values are far below the criterion limit (Hex less than or equal to one) as per the European Commission on Radiation Protection reports, the terrestrial soils from this city has no high exposure for either inhabitants and can be used as a construction material without posing any significant radiological threat to the population.  1.6 Conclusion   Gamma ray spectrometry has been used to investigate the radioactivity concentrations of 238U, 40K and 232Th in soil samples collected from Ogun State. The activity profile of radionuclides showed the existence of low level activity in the studied locations. The mean activity concentrations of 238U, 40K and 232Th, is 1.67±0.35 Bqkg−1, 280.52±1.87 Bqkg−1 and 46.91±1.87 Bqkg−1 respectively, were obtained from all the soil samples studied. These values fall within the lowest range of those measured at worldwide scale reported by other authors. The mean gamma absorbed dose rates and the annual effective dose rate calculated is 40.88 nGy.h-1 and 0.05 mSv respectively, these which are lower than the worldwide average value. The radiation hazard indices obtained are far less than the critical value of unity. Though, the result showed that the radiation levels in the cement factory and adjacent village are higher than those obtained in Covenant University location far from the factory all the obtained were within the recommended safe limit. The present study is the first to establish a baseline data of naturally occurring and anthropogenic radionuclides for the study area most especially for the cement factory. Based on our results, we conclude that the soil of the study area do not pose any radiological health hazard to the people of the area.     Usikalu et al./ IERI Procedia  00 (2014) 000–000 5 (I)                           (II)                          (III)                    Fig.2 (I) Correlation between 238U, and 232Th concentrations; (II) correlation between 238U and 40K concentrations; (III) correlation between 232Th and 40K concentrations  6 Usikalu et al./ IERI Procedia 00 (2014) 000–000  Table 1: Activity Concentrations in the soil samples  Code Location Number of Samples 238U (Bq kg-1) 40K (Bq kg-1) 232Th (Bq kg-1)       NE1 Ewekoro North 5 2.56±0.08 276.21±13.25 56.62±1.96 NE2 Ewekoro South 5 1.83±0.08 261.54±12.67 51.70±1.79 NE3 Ewekoro East 5 1.60±1.60 342.08±14.17 44.78±1.83 NE4 Ewekoro West 5 1.83±1.83 261.54±13.38 51.57±1.89 NN1 Owowo North 5 2.62±0.08 244.11±13.38 61.69±1.89 NN2 Owowo South 5 2.61±0.10 296.40±14.90 57.50±2.02 NN3 Owowo East 5 1.78±0.09 280.42±14.62 50.73±1.85 NN4 Owowo West 5 1.81±0.08 283.17±15.43 50.07±1.93 NU1 Cov. Univ. North 5 0.62±0.07 301.1513.55 30.28±1.81 NU2 Cov. Univ. South 5 0.62±0.06 243.35±12.57 30.23±1.87 NU3 Cov. Univ. East 5 1.07±0.06 287.17±15.43 38.87±1.78 NU4 Cov. Univ. West 5 1.07±0.07 289.10±15.19 38.84±1.80 Range   0.62-2.61 243.35-342.08 30.23-61.69 Mean   1.67±0.35 280.52±14.04 46.91±1.87   References [1] Tzortzis M and Tsertos H 2004 Natural radioelement concentration in the Troodos Ophiolite Complex of Cyprus  Seminar submitted to Department of Physics, University of Cyprus 1-21 [2] Abdul Jabbar, Waheed Arshed, Arshad Saleem Bhatti, Syed Salman Ahmad,  Perveen Akhter, Saeed-Ur-Rehman, Muhammad Iftikhar Anjum. Measurement of soil radioactivity levels and radiation hazard assessment in southern Rechna interfluvial region, Pakistan. Environ Monit Assess (2010) 169:429–438. [3] Avwiri, G.O. 2005 .Determination of Radionuclide Levels in Soil and Water around Cement Companies in Port Harcourt; J. Appl. Sci. Environ. Mgt. 2005, Vol. 9 (3) 27 – 29. [4] White, G.R. (1981). Concrete Technology, 3rd Ed. John . Delmar Publishers, USA, 18 – 19. 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Specific activity and hazards of Archeozoic Cambrian rock samples collected from the Weibei area of Shaanxi, China. Radiation Protection Dosimetry, doi:10.1093/rpd/nci339. Acknowledgements The first author acknowledges the financial support of Abdus Salam Centre for Theoretical Physics (ICTP) for Junior Associate Award.  

Investigation of gamma radiation levels in soil samples collected from some locations in Ogun State, Nigeria.

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Investigation of gamma radiation levels in soil samples collected from some locations in Ogun State, Nigeria.

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