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Radioactivity Concentrations in Soil Samples from Kandam, Gyalgyal, Burmawan masaka, Dinbisu and Giyawa Mines in Wurno LGA, Sokoto State, Nigeria

Aims: This study was conducted in a bid to ascertain the concentration of NORMS in the soil samples dugout of some mining sites in Kandam, Gyalggal, Burmawan masaka, Dinbisu and Giyawa town in Wurno LGA, Sokoto State Nigeria. The concerns about NORMS radioactivity in the environment are frequently linked to natural radioactivity which is more of primordial radionuclides. Study Design: A total number of nine soil samples were randomly collected for this study. The randomness was in order to represent over 90% of the sample population of different mines in Wurno LGA, Sokoto state for the analysis of gamma-ray spectrometry of High Purity Germanium (HPGe) detector coupled to a Multi-Channel Analyzer (MCA). Original Research Article Ahijjo et al.; AJR2P, 1(4): 1-9, 2018; Article no.AJR2P.45083 2 Place and Duration of Study: Department of Physics, Usmanu Danfodiyo University, Sokoto, Nigeria, between August 2015 and June 2016. Methodology: The concentrations of the radionuclides ( 226 Ra, 232 Th and 40 K) were ascertained through a high-resolution gamma-ray spectrometry of HPGe detector coupled with a Multi-Channel Analyzer, Centre for Advanced Studies in Physics (CASP), Government College University (GCU), Lahore, Pakistan. The activity concentrations of 226 Ra, 232 Th and 40 K in the soil samples were obtained and used to calculate the radiological parameters ( eq Ra , ex H , in H , Abs D and Eff D ) in order to assess the radiological impacts on the inhabitants. Results: The mean activity concentrations for Ra, Th and K in the soil samples were found to be 58.34, 53.76 and 679.70 1 Bqkg while the radiological hazards parameters revealed mean values of 187.55 1 Bqkg , 0.51, 0.66, 87.77 1 . nGy h  and107.64 1 Svyr   for eq Ra , ex H , in H , Abs D and Eff D respectively. These were compared with the results of similar studies conducted elsewhere and around the world. It was noticed that K contributes the highest level of radioactivity in this study which could enhance the amount of background radiation received by the population in the study area. The activity concentration unveiled from the soil samples were considerably lower for Ra and Th when compared to the activity of K. The mean value of the dose calculations shows that an elevated exposure to radioactivity by the inhabitants around this mine is eminent. Conclusion: Cancer and various forms of ailment due to radioactivity exposure are further anticipated for the workers in the pits and the dwelling communities.


INTRODUCTION
The basic premise of this research is on the philosophy of ICRP, UNSCEAR, USEPA, WHO and IAEA that strengthen the effort of radiological protection. It was as well conceptualised in preventing the deterministic effects of exposure to environmental radioactivity, and also reducing the occurrence of the stochastic effect of cancer and other relative ailments. Evidence has been established that the major sources of human exposure to ionising radiations are the natural sources [1].
This means that there is a quest for individual protection by determining exposure limits or regulation on the risk of eminent exposure to radiological impacts in the environment [2].
The recent challenges in the global economy have raised the dependence on mineral extraction, exploration, mining etc. to an alarming level [3].
Materials like sand, gravel, rock, talc, asbestos, limestone etc. are dramatically harnessed from mining for aggregates, concretes, roofing slates, cement, ceramics etc. These are enjoyed with relatively high exposure to impurities inform of toxics to health status and pollution to the environment [4]. The exposure to radioactivity in the environment was found to account for roughly 85% of annual exposure dose received by the populations around the world [5].
Radioactivity exposures arise in the mining sites and their neighbourhood through three significant pathways which includes external gamma radiation from ores, inhalation of dust containing long-lived alpha-emitting radionuclides and inhalation of the short-lived decay progenies of some radionuclides [6].
Various studies concerning environmental radioactivity have provided information on the sources and levels of background radiation in some observed changes on radioactivity levels and particular areas, but little evidence have unveiled and assessed the activities in the mining communities that could lead to elevated exposure of commonly occurring radionuclides of 40 K, 238 U, 226 Ra, 232 Th, 137 Cs with an interest on the maladies to human health [7].
Hence, this paper attempts to unveil the concentration of radioactivity in the soil samples collected from the mines. The radiological tendencies of the inhabitants around these mines will be also assessed through theoretical calculations. The results of this study may also signal some dangers attributable to indiscriminate mining of raw materials like Kaolin, Gypsum, Limestone etc., from the study area in Sokoto state.
The outcome of this finding could be added to the obtainable data of similar studies in other locations. Similar studies were conducted by [8,9,10,11,12,13,1] in a bid to unveil the environmental radioactivity and elemental analysis from environmental samples of farmland or mining sites.

MATERIALS AND METHODS
The sampling was considered based on proportions, representation of the sample, homogeneity, sample points code and size (taking the weight) respectively. Soil samples were randomly collected from five mines in Wurno LGA, Sokoto State in a fashion that satisfies the outlines according to [14,15,16,17,18]. The soil samples were collected with the aid of a cleaned hand auger from 0 cm depth where hips of excavated soil from the mines are dumped in a distribution of 5 different points at about 25 km apart. Three separately collected samples were homogenised within 50 cm parts to achieve a 95 to 98% representation of the soil for a particular location. The weight of the collected samples was measured so as to achieve a 2.5 kg gross weight of the sample from the field. They were then parked into a 300 ml plastic container, labelled with a distinct code and then stored in their sealed form before shipping to a laboratory for further experimental exercise. They were the measurement by gamma-ray spectrometry of HPGe detector coupled with an MCA. The samples were dried for seven days under the ambient temperature of the air and manually sorted by removing stones, leaves and other organic particles. They were gently dried at 75 o C for 24 hours in an oven for a careful removal of potential residual moisture and to avoid loss of volatile radionuclides to enable equilibration [19].
They were crushed, pulverised and homogenised with the aid of a mortar and pestle and then sieved through a standard mesh of 2.5 mm sizes using a vibratory sieve shaker to enable uniform distribution of radionuclides [20].
The samples were hermetically sealed with a PVC tape to prevent gaseous nuclide flux in a standard 250 ml Marinelli beakers for 4 weeks to enable equilibration of the radionuclide progenies and to minimise partial accumulations of the radionuclides after preparation. To attain radioactive secular equilibrium, 4 weeks maximum duration was set between 222 Rn (radioactive noble gas), its decay products ( 214 Pb and 214 Bi) and radium ( 226 Ra), from the 238 U decay series. For the 232 Th decay series, the radon isotope ( 220 Rn) poses no serious problem in equilibration due to its short half-life of 55 seconds and in the 40 K decay series, no equilibrium is accounted for [20].
The techniques of gamma-ray spectrometry of HPGe detector was used to count all the soil samples in this study as outlined by Umar et al. [21].

Gamma-ray Spectrometry
The measurement of the activity concentrations of the radionuclides was performed using a Ptype coaxial HPGe detector in a low-background configuration. The HPGe was made of concentric cylinders that were closed at the end. The Peakto-Compton ratio of the HPGe detector was 1332.5 keV at the photopeak of 60 Co. The detector was housed in a 12 cm of lead shielding to reduce the interference of background radiation from the surrounding with a cooling system of liquid nitrogen in a vertical cryostat Dewar (50 litres) to suppress the leakage current [22].
The detector cooling was incorporated for the system to enhance operation on low temperature for optimal performance of the energy and detection efficiency during operation that requires cooling below 110 o C. The detector system was fully automated with a multi-channel analyser that was installed in a Personal computer for data acquisition. A fixed geometry was maintained for the standard source and the samples by choosing a 250 ml Marinelli beaker for the coaxial HPGe detector. The signals processing in the gamma-ray spectrometry setup used the main amplifier which was incorporated with an efficient pile-up ejector in the multi-channel buffer that consists of an analogue-to-digital converter (ADC).
For a linear amplification, the pulse height appears proportional to the gamma-ray energies absorbed. The pulses from the amplifier were then sorted by their pulse height and then converted to a digital number referred to as channel by the analogue-to-digital converter (ADC) in the multichannel analyser (MCA). The identification of individual radionuclides was then achieved with the aid of gamma-ray analysis software, GENIE 2000 of Canberra Company. It was used to acquiring spectrum signal for analysis in the MCAs. It was also used to perform Multiple Channel Analysis control, spectral display, basic spectrum analysis for the gamma-ray spectroscopy and quality control [23].
The spectroscopic windows in the MCA were used for energy and efficiency calibration options and peak to total calibration which were maintained and stored for use. The spectrum results were obtained from the MCA spectra of the gamma-ray photopeaks of the typical radionuclide in the sample as well as all the interactions ranging from scattering events to photo peaks that were initiated by photoelectric effects. The two well-known The efficiency of the HPGe detector was 60% with a resolution of 1.85 keV in its full-width at half maximum (FWHM) of the gamma-ray energy line of 60 Co at 1332.5 keV. A unified preamplifier was connected to the terminal for varying transmissions of the signals. The energy calibration of the detector was performed with the calibration standard source containing the following radionuclides: 109  K are known to decays directly in gamma-ray by their common emission lines of 661 keV and 1460 keV. A linear fit was then used to obtain the energy calibration parameters. The amplifier gain was set such that 1 spectrum channel corresponds to 0.5 keV. The linear relationship of gamma-ray energies (0 -2000) and channel numbers (0 -6000) was set within the ROI obtained from the linear equation 1 by the computer [24,25].
where: E is the energy in keV, 1 A and 2 A are calibration constant for a given geometry.
Hence, a linear relationship was obtained for energy in keV against respective channel number.
The activity concentration of a radionuclide in the soil samples is given by equation (2): Where c A is the activity concentration of a particular nuclide in of 1 Bqkg  . E N the net count at the interest peak energy as the corrected background counts of the corresponding fullenergy peak,   is the absolute full-energy peak detection efficiency, p  is the gamma-ray emission probability, c t is the counting time in 86,400 seconds, and m is the mass of the samples in kilogram. The minimum detectable activity (MDA) for each radioelement was obtained by equation 3 according to Gilmore and Hemingway [23,26].
Where D L is the detection limit under the background counts B such that: The errors in the measurements were expressed in terms of standard deviation (±σ), where σ is expressed as in equation 5 [23,26].  The assessment of radiological hazard to the inhabitants around these mines due to exposure to ionising radiation from the commonly occurring radionuclides in the environment was based on the guidelines of [6]. To account for the annual effective dose rates, the conversion coefficient from absorbed dose in air (

Activity Concentration
The spectrometric results revealed a wide range of spectra from the counting of the samples. The spectral signals were used for the identification of different radionuclides from the soil samples. The results of activity concentrations of 226 Ra, 232 Th and 40 K from the soil samples are presented on Table1 while Table 2 presents the radiological hazards parameters. Th and 40 K on the inhabitants of these communities, the absorbed dose and the annual effective dose rates were calculated using equations 9 and 10. The mean absorbed dose in the ambient air due to terrestrial gamma-ray was found to be 87.77 B q k g  for 226 Ra, 232 Th and 40 K according to UNSCEAR report [6]. The concerns on this hike in the values of radioactivity could be prominent due to the prevalence of younger granite rocks, Feldspars and Phosphate rocks in the Iullemeden basin where Wurno LGA form apart [28].
Most precious minerals that are mined in parts of Sokoto basin are also from quartz-mica rocks, granites rocks and Monazites which are known to be responsible for the higher level of radioactive exposure to inhabitants from their embedded primordial sources [12,11].
The results of this study were found in good agreement with the results obtained in the work of other researchers in Nigeria and around the world. The results are presented in comparison with other results in Table 3.

CONCLUSION
In this paper, the method of gamma-ray spectrometry has been used to ascertain the concentration of radioactivity from some mines in Wurno LGA, Sokoto state, Nigeria. The activity concentration of 40 K was found topping the chart of the results of natural radioactivity of the commonly occurring radionuclides from the mines. 226 Ra, 232 Th and 40 K were found significantly higher in a concentration above the world mean values which entails an enhanced background radiation levels in the study area. There are also significant levels of some radiological parameters unveiled in this study. Hence, there are potential dangers of exposure to radioactivity to the workers in these mines and the general public dwelling in these communities. The soil from this mine must be carefully handled in case of any domestic or industrial needs to mimic radiological hazards.
Lastly, due to lack of sufficient accounts on the level of radioactivity in the soil of mines from these localities, the results obtained from this study stands a good chance of baseline data for research on the radioactivity measurement in the environment and mining sites of this region.
However, effective radiation monitoring measures are recommended to enable the frequent exercise of determining radioactivity levels so as to checkmate any potential radiotoxic burden on the general public.