Journal of Radiation Research and Applied Sciences 8 (2015) 216e220. Available online at ScienceDirect

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1 HOSTED BY Available online at ScienceDirect Journal of Radiation Research and Applied Sciences journal homepage: Radioactivity concentration variation with depth and assessment of workers' doses in selected mining sites C.U. Nwankwo a,b,*, F.O. Ogundare a, D.E. Folley a a Department of Physics, University of Ibadan, Nigeria b National Institute of Radiation Protection and Research, University of Ibadan, Nigeria article info Article history: Received 22 November 2014 Received in revised form 4 January 2015 Accepted 10 January 2015 Available online 2 January 2015 Keywords: Mining Gamma radiation spectrometry Workers' effective dose Dose-rate abstract Mining workers are exposed to radiation in the process of extracting minerals from the earth crust. In this research, activity concentration of the radionuclides in samples collected at different depths in Komu (0e220 ft) and Olode (0e0 ft) mining sites, Oyo State, Nigeria and the associated workers' radiological risks were assessed. Gemstones from these sites are mined for local and international markets. The radionuclide contents of the samples were determined using Gamma spectroscopy technique. At Komu, 28 U and 22 Th concentrations, with few exceptions, increased with depth while that of 40 K had no defined pattern. At Olode site, 28 U and 22 Th concentrations decreased with depth while that of 40 K was almost constant. Internal hazard indices at Komu in some cases indicated an unacceptable level of risk to workers. Workers' doses would have been underestimated by between 12 and 55% if the activity concentrations of samples in the pit were not included in the calculation. Copyright 2015, The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( 1. Introduction Naturally occurring radionuclides are the major sources of ionizing radiations in the environment. Human exposure to these ionizing radiations, if the level is enhanced beyond background, could lead to detrimental health effects. Enhancement of radiation level in the environment is usually due to human activities (Tubosun et al., 201) such as mining and milling of mineral ores, nuclear fabrications, and handling of the fuel cycle tail end products (Saleh, 2011). Enhanced level of natural radioactivity through these activities may cause radiation doses to workers and/or the public in order of several msv/yr (Jibiri & Temaugee, 201; Stoulos, Manolopoulou, & Papastefanou, 200). Part of the safety analysis recommended by the IAEA includes estimation of radiation doses likely to be received by workers during operation and estimation of doses and risks to the public (IAEA, 2002). Hence there is need for the assessment of radiation doses of workers in human activities that may enhance radiation levels to ensure that they do not exceed regulatory limits. Presently there are scanty information from Africa on activity concentrations of soils and individual doses from * Corresponding author. National Institute of Radiation Protection and Research, University of Ibadan, Nigeria. Tel.: þ address: rapuluchi@yahoo.com (C.U. Nwankwo). Peer review under responsibility of The Egyptian Society of Radiation Sciences and Applications /Copyright 2015, The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (

2 217 mining activities which is the most prominent activity that could cause elevated radiation level in most developing countries where illegal mining is prominent. Previous reports on radioactivity measurements in mining locations around the world include the assessment of the radionuclide contents in minerals and soil samples from mining sites in America (USEPA, 2008), Australia (Cooper, 2005; Long, Sdraulig, Tate, & Martin, 2012; Senior & Chadderton, 2007) and Nigeria (Ibrahim, Akpa, & Daniel, 201; Jibiri & Temaugee, 201; Tubosun et al., 201, 2014). Except for Senior and Chadderton (2007), none of these studies investigated the variation of activity concentration with depth, a knowledge which is important for a realistic assessment of the radiological risks to the miners. Furthermore, assessments of workers' doses in the studies were without reference to the fraction of time spent in the pits (Ibrahim et al., 201; Tubosun et al., 2014). The calculations were done using only activity concentrations of samples collected on surface of mining locations. A more realistic dose calculation should however take into consideration the variation of activity with depth. In this study, the radionuclide contents of samples collected at different variation of depths from two major mining sites located in Oyo State of Nigeria will be assessed. Tourmaline and Pegmatite, known to house radioactive minerals (Petta, Campos, Sindem, Nascimento, & Meyer, 2009) are mined in these sites. The occupational doses of the workers in the mining site will also be assessed taking into consideration the separate time spent by the workers in the pit and on the surface. 2. Materials and methods 2.1. Sample collection and preparations Samples (soil þ minerals) analyzed were collected at the surfaces and mining pits of different depths at Komu (0e220 ft) and Olode (0e0 ft) Mining Sites. Tourmaline, mica and pegmatite are the minerals of interest at Komu while it is aquamarine and pegmatite at Olode. The samples were sun dried and carefully placed in an oven for drying at a temperature of 150 C to achieve a constant weight, then pulverized and sieved with a 2 mm aperture mesh sieve. About 650 g of each sample packed into a tightly closed Marinelli beaker and sealed with a PVC tape was stored for at least one month to ensure secular equilibrium between the parent radionuclides and their respective daughters Gamma analysis The samples' radionuclide contents were analyzed by Gamma-ray spectrometric measurements using ORTEC high purity germanium detector (relative efficiency of 20%, energy resolution of 1.85 kev at 12.5 kev) coupled to ORTEC Multi- Channel Analyzer (MCA). Maestro evaluation software was used for spectrum acquisition and processing. The energy calibration was made using different point sources in the energy range keve kev while the efficiency calibration of the detector was made using a 650 g mixed CANBERRA soil standard containing 125 Sb, 155 Eu, 54 Mn, 65 Zn and 40 K. The absolute efficiency curve was fitted to a standard efficiency function of the form proposed by Gray and Ahmad (1985) ¼ 1 E " X 7 n¼1 P n ½In EŠ n 1 # where P n are the parameters of the fitting function and efficiency at energy E. 2.. Activity concentration (1) is the The specific activity concentration of each radionuclide in the samples was determined using Eq. (2) NC i A i ¼ (2) y i M T where A i is the ith radionuclide concentration, NC i ¼ net count of the ith radionuclide, ¼ detector efficiency at the energy of the ith radionuclide; y i ¼ the emission probability of the ith radionuclide, M ¼ Mass of the soil sample in kg, T ¼ counting time (10 h). The gamma lines of 228 Ac, 212 Bi, 212 Pb and 208 Tl were used to determine 22 Th while 214 Bi and 214 Pb were used for 28 U and kev for 40 K Dose rate The absorbed dose rate in air at 1 m above the ground surface was estimated based on the provision by UNSCEAR (2000) as follows: DRðnGy=hÞ ¼0:462A U þ 0:604A Th þ 0:0417A K () where DR is the absorbed dose rate in ngy/h and A U,A Th and A K are the activity concentrations of 28 U, 22 Th and 40 K respectively. The annual effective dose, E (in msv yr 1 ), to personnel from external exposure was calculated using the Eq. (4) E i ¼ DR i OF CF (4) where E i is the annual effective dose due to ith radionuclide. CF is the conversion factor for absorbed dose in air to external effective dose in adults and is given as 0.7 Sv Gy 1 (UNSCEAR, 2008). DR i is the absorbed dose rate at 1 m above the ground due to the ith radionuclide. OF is the occupancy factor. When the workers are assigned to work in the pits, they usually spend about h in the pit and 5 h on the surface. Hence, their effective dose E can be calculated as follows: E i ¼ DR i;depth OF pit CF þ DR i;surface OF surface CF (5) where OF pit ¼ hr day 1 5days week 1 52weeks yr 1 OF surface ¼ 5hr day 1 5days week 1 52weeks yr Radiation hazard indices In addition to the gemstone that is being mined at Komu and Olode site, there are evidences that sand and stones from the sites are also being used for building construction. In order to assess the radiological suitability of the sand and stones for use as building construction, the radium equivalent index,

3 218 Table 1 e Mean Activity concentrations (Bqkg 1 )of radionuclides in the soil samples of Komu Mining Site. Depth (ft.) 28 U 22 Th 40 K ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±.02 Table e Radiation hazard indices for Komu mining site. Depth (ft) Ra eq (Bqkg 1 ) H ex H in I yr World mean External hazard index, Internal hazard index and gamma activity index are important parameters to be considered. I gr ¼ A Ra 150 þ A Th 100 þ A K 1500 (9) Radium equivalent activity (Ra eq ) Ra eq is a common radiological index used to compare the specific activities of materials containing 28 U, 22 Th and 40 K by a single quantity, which takes into account the radiation hazards associated with them (Avwiri, Osimobi, & Agbalagba, 201; Baratta, 1990). Ra eq is mathematically defined by Beretka and Mathew (1985) and proposed by UNSCEAR (2000) as: Ra eq ¼ A U þ 1:4A Th þ 0:077A K (6) The value must be less than 70Bq for the radiation hazard to be negligible External hazard index (H ex ) H ex considers only the exposure risks due to gamma ray and is defined as (Beretka & Mathew, 1985) H ex ¼ A Ra 70 þ A Th 259 þ A K Internal hazard index (H in ) H in is used to quantify internal exposure and is defined as (Abbady, 2005; Avwiri et al., 201; Beretka & Mathew, 1985; Hrichi, Baccouche, & Belgaied, 201; Jibiri & Temaugee, 201). H in ¼ A Ra 185 þ A Th 259 þ A K (8) 4810: The values of the indices (H ex, H in ) must be less than unity for the radiation hazard to be negligible (Agbalagba, Avwiri, & Chad-Umoreh, 2012; Diab, Nouh, Hamdy, & El- Fiki, 2008) Gamma activity index (I gr ) I gr is used to estimate the g-radiation hazard associated with the natural radionuclide in investigated samples. It is defined as follows: Table 2 e Mean activity concentration (Bqkg 1 ) of the radionuclides in the soil samples of Olode. Depth (ft) 28 U 22 Th 40 K ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 28.2 World mean (7). Results and discussion.1. Activity concentration of radionuclides detected in the samples The activity concentrations of radionuclides in Komu and Olode are presented in Tables 1 and 2 respectively. The values are generally within those that have been reported for mining sites for precious opal (Senior & Chadderton, 2007), different minerals (Cooper, 2005) and ore from quarries (Long et al., 2012) in Australia. The values are however generally below those reported for titanium (148e1665 Bq/kg) and zircon (219e48100 Bq/ kg) mines in America (USEPA, 2008). A possible reason for this is that titanium and zircon in the America sites are generally richer in radioactive materials than tourmaline and pegmatite in the sites employed in the present study. At Komu, the activities of the radionuclides have no definite pattern with depth except for 28 Uand 22 Th whose concentrations increased from 120 ft up to 220 ft. This pattern is similar to what was observed by Senior and Chadderton (2007) for a drill hole in Australia. The activity values at Olode are about 4e6 times the worldwide background average. For Olode, at depths greater than zero, 28 U activity concentration was greater than that of 22 Th, a pattern common to all the samples. The concentration of 40 K varied in a non-systematic way with depth. There was no definite pattern of variation for 28 Ubut 22 Th activity decreased from 0 ft to 25 ft, 40 Kincreased from0ftto20ft.absenceofdefinedpatternatdepthsclosetothe surface may be due to contamination of samples at this level with those brought up from deeper depth during the mining process. Avwiri et al., 201 also reported that there was no regular variation of radiation with lithology depth in a drilled borehole in Nigeria. 22 Th activity concentrations in this study for Olode sites are similar to those reported for soil, rock, water and mine waste by Tubosun et al. (2014) for the same site, while the activity concentration of 28 Uand 40 Karelower. Table 4 e Radiation hazard indices for Olode mining site. Depth (ft) Ra eq (Bqkg 1 ) H ex H in I yr

4 219 Table 5 e Comparison of absorbed dose rate and annual effective dose received by the workers at the sites. Depths(ft) Olode Komu D (ngy/hr) E (msv/yr) % Difference D (ngy/hr) E (msv/yr) % Difference e e e e e e e e e e e e 70 e e e e e e e e e e e e World Mean e e % Difference ¼ this is the percentage difference between effective dose for workers at the surface (calculated assuming 8 working hours per day) and the effective dose for those that work partly in the pit(calculated using h for work in the pit and 5 h on the surface)..2. Radiation hazard indices Ra eq for Komu ranged from to 1.84 Bqkg 1 while that of Olode ranged from to Bqkg 1 (See Tables and 4). The values from the two mining sites are below the permissible limit of 70 Bqkg 1 (UNSCEAR, 2000). H ex for Komu ranged from 0.4 to 0.90 while that of Olode ranged from 0.12 to The values obtained for both sites are less than unity and as such none of the minerals considered in this work are a major source of external radiation exposure. H in ranged from 0.17 to 0.89 for Olode mining site while it ranged from 0.45 to 1.46 for Komu mining site. The values for Komu mining site at depth 70, 120 and 220 ft are greater than 1 which indicates that prolonged stay may constitute a health hazard. I gr for Komu mining site indicated annual effective dose greater than 1 msv/yr at some depths, while for Olode it is only at 15 ft... Dose assessment The absorbed dose rates for workers at Komu mining site are summarized in Table 5. These values obtained at the different depths are higher than the worldwide mean of 57 ngy hr 1. The absorbed dose rates for workers at Olode shown in are lower than the worldwide mean except at 15 ft. The calculated annual effective dose equivalents for the workers at Komu are higher than the worldwide mean outdoor effective dose (70 msv) while that of Olode mining site are lower. Neglecting activity concentrations of samples from the pit, but using those of surface samples and 8 working hours for workers dose calculation would have resulted in the underestimation of doses of those who work in the pit by between 12 and 55%. 4. Conclusion Activity concentrations, dose rates and annual effective dose at Komu were higher than the corresponding values at Olode. The annual effective doses of workers at both sites were lower than even 1 msv/yr recommended by ICRP for members of the public. The activity concentrations of 28 U and 22 Th and calculated total dose rates for Komu mining site were found to be higher than the world background mean value. The internal hazard indices indicated that continuous exposure could lead to some level of health risk. However, since the values obtained were still within the limiting values recommended by UNSCEAR (2000) and ICRP (1991), the mining activities need not be under regulatory control, however, the workers at the mine need to be wary of prolonged exposure in the sites. Generally, the activity concentrations at the two sites had no definite pattern of variation with depth. Doses calculated without reference to variation of activity concentration with depth could lead to underestimation of doses. references Abbady, A. (2005). Assessment of the natural radioactivity and its radiological hazards in some Egyptian rock phosphates. Indian Journal of Pure and Applied Physics, 4, 489e49. Agbalagba, E. O., Avwiri, G. O., & Chad-Umoreh, Y. E. (2012). Gamma-spectroscopy measurement of natural radioactivity and assessment of radiation hazard indices in soil samples from oil fields environment of Delta State, Nigeria. Journal of Environmental Radioactivity, 109, 64e70. Avwiri, G. O., Osimobi, J. C., & Agbalagba, E. O. (201). Evaluation of natural occurring radionuclide variation with lithology depth profile of Udi and Ezeagu local government areas of Enugu State, Nigeria. International Journal of Engineering and Applied Sciences, 4(), 1e10. Baratta, E. J. (1990). Radon, radium and uranium in drinking water (pp. 20e21). Washington DC: Lewis Publisher. Beretka, J., & Mathew, P. J. (1985). Natural radioactivity of Australia building materials industrial wastes and byproducts. Health Physics, 48, 87e95. Cooper, M. B. (2005). Naturally occurring radioactive materials (NORM) in Australian industries e Review of current inventories and future generation. A Report prepared by EnviroRad Services Pty. Ltd for the Radiation Health and Safety Advisory Council (ERS-006). Diab, H. M., Nouh, S. A., Hamdy, A., & El- Fiki, S. A. (2008). Evaluation of natural radioactivity in a cultivated area around a fertilizer factory. Journal of Nuclear and Radiation Physics, (1), 5e62. Gray, P. W., & Ahmad, A. (1985). Linear classes of Ge(Li) detector efficiency functions. Nuclear Instruments and Methods in Physics Research A, 27, 577e589. Hrichi, H., Baccouche, S., & Belgaied, J. (201). Evaluation of radiological impacts of tenorm in the Tunisian petroleum industry. Journal of Environmental Radioactivity, 115, 107e11.

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