|Year : 2018 | Volume
| Issue : 1 | Page : 51-54
Assessment of natural radioactivity levels due to 238U, 232Th, and 40K in the soil samples of Raichur district, Karnataka, India
S Rajesh1, BR Kerur2
1 Department of Physics, Reshmi Postgraduate College, Kalaburagi, Karnataka, India
2 Department of Physics, Gulbarga University, Kalaburagi, Karnataka, India
|Date of Submission||31-Jan-2018|
|Date of Decision||21-Feb-2018|
|Date of Acceptance||17-Mar-2018|
|Date of Web Publication||31-May-2018|
Dr. B R Kerur
Department of Physics, Gulbarga University, Kalaburagi, Karnataka
Source of Support: None, Conflict of Interest: None
Natural radioactivity measurement, dose assessment, and interpretation of radiological-related parameters and radiation monitoring of the region are crucial aspects from the public awareness and environmental safety point of view. The present paper discusses the results of activity concentration of the natural radionuclides 238U, 232Th, and 40K in the soil samples collected from Raichur district. ASTM procedure was followed for the sample collection and preparation for gamma spectrometric measurements. Gamma spectrometry-based 4” × 4” NaI (Tl) scintillation detector was employed for estimating activity concentrations of the gamma-emitting radioelements. Each sample was measured for a counting period of 60,000 s. The activity concentrations of the radionuclides 238U, 232Th, and 40K were found in the range 10–119, 8–285, and 46–1646 Bq/kg, respectively. The activity concentrations of the radionuclides and the dose-related parameters for the samples were found to be comparable with the global literature values, except few samples. The data generated from this study are the baseline radiological data of the region for future references.
Keywords: Activity, dose, gamma spectrometry, radioactive equilibrium, radioactivity
|How to cite this article:|
Rajesh S, Kerur B R. Assessment of natural radioactivity levels due to 238U, 232Th, and 40K in the soil samples of Raichur district, Karnataka, India. Radiat Prot Environ 2018;41:51-4
|How to cite this URL:|
Rajesh S, Kerur B R. Assessment of natural radioactivity levels due to 238U, 232Th, and 40K in the soil samples of Raichur district, Karnataka, India. Radiat Prot Environ [serial online] 2018 [cited 2020 Jan 18];41:51-4. Available from: http://www.rpe.org.in/text.asp?2018/41/1/51/233647
| Introduction|| |
Radiations present in the environment comprise terrestrial and extraterrestrial radiations. Hence, the primary radioactivity data collection and the derived radiological-related parameters are crucial aspects from the public awareness and environmental safety point of view. The natural radioactivity present in soil, rock, sand, and other environmental materials contributes significantly to the collective dose received by the living system. Gamma-ray spectrometry is the commonly used analytical technique for the estimation of 238 U,232 Th, and 40 K in various environmental samples. External contaminants entering a soil body through wet or dry precipitation, such as radionuclides, trace elements, or organic compounds, behave differently with regard to each soil type according to the absorption properties, texture, density, humidity, and other factors. The present study estimates the external gamma dose rate, which creates public awareness about the radiation and provides the necessary information about the radiological protection.
Geology of study area
The study has been carried out over Raichur district of Northeast Karnataka. It lies between latitude 15° 33′–16° 34′ N and longitudes 76° 14′–77° 36′ E covering an area approximately 8000 km 2 and at the altitude varying from 1100 to 1600 m above the mean sea level. This area is a rich source of granite. The abundance of granite has increased the mining activity and has become an occupation for the public over there. Six types of granites are known to be intruding the schist belt, and all of them are igneous type rocks. Due to ruthless mining activity, more and more granite industries are finding their way around the region. Hence, the knowledge of the activity concentration levels of naturally occurring radionuclides in soils and the assessment of possible radiological risks in this region are very essential.
| Materials and Methods|| |
A total of 90 soil samples were collected from the study region. The standard procedure was followed for soil sample collection and preparations, where surface soil samples were collected over an area 50 cm × 50 cm × 5 cm depth and mixed thoroughly, and about 2–3 kg of each sample was collected. After collection pebbles, dried leaves, roots, and other mixed materials were removed from the soil samples. The samples were placed in a hot air oven for drying at 110°C for 24 h to ensure that the moisture is completely removed. All samples were pulverized to get fine powder and sieved through a 200-mesh sieve to separate the unevenly crushed soil particles. Each pulverized sieved sample was then transferred to a 250 mL cylindrical plastic (PVC) container. The weights of the empty and sample-filled containers were taken by an electronic balance. The net weights of the samples, dates, and sample IDs were recorded in the register. The same information was also written on the top of the containers. The soils were poured in the containers and sealed with an adhesive, weighed, and then stored for a period of 4–5 weeks to attain secular equilibrium between radon (222 Rn) and thoron (220 Rn) and its daughter products before subjecting to gamma spectrometric analysis.
The activities of 238 U,232 Th, and 40 K in samples were measured using NaI (Tl) detector-based gamma spectrometry system. The output of the detector was analyzed using a PC-based 1K multichannel analyzer system (WinTMCA-32). The spectra were then analyzed using the LSQ technique. The detector was surrounded by 3” thick lead shield on all sides to reduce the background radiations originating from building materials and cosmic rays. Efficiency calibration of the detector system was performed using IAEA standards RGU-1 RTh-1 and RG-K 1764 KeV, 2614 KeV and 1460 KeV in the geometry available for sample counting, the same geometry is maintained for all samples. The standard source was counted for 10,000 s for good statistics. Photopeak areas of the most prominent photopeaks were calculated, and most environmental samples contain very low level of natural and manmade radionuclides. Therefore, a low detection level is desirable for gamma spectrometric analysis of environmental samples. Minimum detectable activity of the NaI (Tl) gamma spectrometry system has been estimated.
Each sample was measured for a counting period of 60,000 s to reduce the counting errors. Assuming that the daughter products of 238 U and 232 Th were in equilibrium, the activity concentration of the radionuclides was estimated. Background radiation was measured and subtracted to get the net count rate for each sample. The spectra were analyzed using the LSQ technique. The activity concentrations were calculated from the intensity of each gamma line, considering the mass of the sample, the time of counting, and the efficiency of the detector.
| Results and Discussion|| |
The results of the reported activity concentrations of the three primordial radionuclides 238 U,232 Th, and 40 K obtained for each of the samples are mentioned in [Table 1]. Mean and range of activity and dose-related parameters prepared from the study region are summarized in [Table 2]. The activity concentrations of 238 U,232 Th, and 40 K for all the samples were found to lie in the range from 10 to 119, 8 to 285, and 46 to 1646 Bq/kg, respectively. In almost all the soil samples, the thorium concentration was found to be higher, which is shown graphically using the Surfer 8.0 software (Golden Software). The contour-map activity concentration of 232 Th is shown in [Figure 1]. Some soil samples showed a high activity of 40 K but less than the world average as the samples were collected from the cultivated lands wherein fertilizers might have been used for the cultivation of land. This is because radium is more susceptible to solubility, whereas thorium is less soluble and hence remained in the soil., [Figure 2] provides Histogram map of comparison of average activity from 238 U,232 Th and 40 K in Raichur district sampling stations. The estimated mean activities values of 238 U,232 Th, and 40 K were found to be comparable within the range of worldwide values. The obtained activity concentration values compared with the world literature values are shown in [Table 2]; except for few samples, higher activity concentration of the radionuclides is observed which is associated with igneous rocks and younger granites, and all the activity values are below the world average values.
|Table 1: Range, mean of activity (Bq/kg), absorbed dose (nGyh-1), and annual effective dose (mSvy-1) of Raichur city|
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|Table 2: Comparison of activity (Bq/kg) for soil samples of present study with other literature data|
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|Figure 2: Histogram showing the comparison of average activity of 238U, 232Th, and 40K in Raichur district sampling stations|
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The absorbed gamma dose rates from the primordial radionuclide concentration in air were calculated for all the samples. The absorbed gamma dose rates due to terrestrial gamma rays at 1 m above the earth's surface were calculated from the concentrations of 238 U,232 Th, and 40 K using the conversion factors 0.604, 0.462, and 0.0417, respectively, as given below:
Where CTh, CU, and CK are the average activity concentrations of 232 Th,238 U, and 40 K, respectively. The estimated absorbed gamma dose values for the sampling stations are shown in [Table 1]. The high activities of granites lead to the higher values of absorbed dose rates. The United Nations Scientific Committee on the Effects of Atomic Radiation suggested the calculation of annual effective indoor dose using the conversion factor of 0.7 SvGy −1 to absorbed dose rate by presuming that people spend about 80% of the time in indoors. Hence, the annual effective indoor dose is calculated using the formula below and the corresponding values are presented in [Table 2]. Calculated annual effective dose (AED) valued are compared with the measured AED values which we measured using the RadEye personal radiation dosimeter. There was a difference between calculated and measured values of AED due to the instrumental error and environmental factors.
| Conclusions|| |
The gamma activity of natural radionuclides 238 U,232 Th, and 40 K was estimated using gamma spectrometry system with 4“×4” NaI (Tl) detector. Moreover, the present study showed a wide distribution of activity concentration among the samples. The soil present in the region rich in granite, gives comparably higher activity concentration. The samples showed higher thorium activity than radium activity as radium is leached out with water, but thorium remains in the soil; hence, thorium activity is relatively higher compared to uranium. In some soil samples, the observed potassium activity is high, and this is due to the usage of potassium-containing fertilizers. [Table 2] shows the activity of 238 U,232 Th, and 40 K in the soil samples which were found to be normal values in comparison to other places of India and world literature values. The present study reveals that the activity values measured are due to natural background radiation level only. 
Financial support and sponsorship
Authors express sincere regards to BRNS for providing the financial support.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]