ISSN 0972-0464
Radiation
Protection
and
Environment
Vol. 34 / Number 1 / January-March 2011
Publication of INDIAN ASSOCIATION FOR RADIATION PROTECTION (IARP)
www.iarp.org.in
Radiation Protection and Environment
/ V
olume
33
/ Number
4
/
October-December
2010 / Pages
1. INTRODUCTION
Radiation is present everywhere in the environment of earth, below the earth and in the atmosphere. Man knowingly or unknowingly is continuously being exposed to the radiation, nature itself being the signiicant source of radiations. Radionuclides are found naturally in air, water and soil and even in human body. Natural radioactivity is common in granites, soil, sand, water and building materials present around us. Natural background radiation is of terrestrial and extraterrestrial origin (UNSCEAR, 2000). The main contribution to terrestrial background radiation is from naturally occurring
radionuclides 226Ra, 232Th and their daughter products and singly occurring natural radionuclides such as 40K, 87Rb present in varying amounts in soil, rocks, granites
and building materials. Some of the radionuclides from these sources are transferred to man through ingestion or inhalation, while the extraterrestrial radiation originates from outer space as primary cosmic rays. Furthermore, because of the occurrence of radionuclides in soil and in vegetation, exposures will occur as a result of ingestion (El-Arabi, 2007).The environmental radioactivity and associated external exposure due to gamma radiation from the environmental materials like soil, rock, water etc., depend mainly on the geological formation and composition of the region (Ramola et al., 2008). Hence
it is present everywhere within us and surrounding environment in different concentrations. Also it is found by many researchers that the accumulated dose can be
high even though activity of these materials is at low level (low level radioactivity). Around the world there are some areas with sizable population that have high background radiation levels. The high background radiation areas are found primarily in Brazil, India and China (Nambi
et al., 1994; Baranwal et al., 2006). Due to the advanced
technology and modernization a person is prone to the internal and external radiation and knowledge of natural radioactivity and the determination of amount of radiation dose received become important.
Soil and other environmental materials are important components of environment that not only contains compounds that support life but also contains signiicant quantity of various radionuclides such as
232Th, 226Ra, 222Rn, 40K etc. the gamma radiations emitted
from which are harmful to the life. External gamma dose rates depend on the activity concentrations of the natural primordial radionuclides 232Th, 226Ra and their decay
products and 40K present in soil and rock, which in turn
depend on the rock formation and geological composition of the region.
In this context, the present work involves the estimation of activity of the primordial radionuclides and associated radiation dose received from soil and building material (granite, sand, brick) samples collected from Shahpur region of Gulbarga district of North Karnataka. The study will provide a baseline data of natural background radiation level of the region, which
NATURAL RADIOACTIVITY LEVELS IN SOME ENVIRONMENTAL
SAMPLES OF SHAHPUR REGION OF NORTH KARNATAKA, INDIA
B.R. Kerur, T. Rajeshwari, N.M. Nagabhushana, S. Anilkumar1, K. Narayani1,
A.K. Rekha1, B. Hanumaiah2
Department of Physics, Gulbarga University, Gulbaga, 1Radiation Safety Systems Division,
BARC, Mumbai, 2 Vice-Chancellor, Babasaheb Bhimrao Ambedkar University, Lucknow, India.
E-mail: kerurbrk@hotmail.com
ABSTRACT: The natural radioactivity due to Radium, Thorium and Potassium in environmental samples
such as soil and building materials contributes to the radiation dose received by human beings signiicantly. For assessing the environmental radiological impact to public it is essential to evaluate the activity levels of these nuclides. Using high-resolution Gamma ray spectrometry system the soil and few building material samples viz., granite, sand, brick collected from Shahpur region of North Karnataka were analysed and the radioactivity levels were estimated. The absorbed dose rate due to natural radionuclides was also calculated and the results are reported in this paper. The results obtained were observed to be normal in comparison with the World literature values for almost all samples whereas granite samples showed relatively higher activity and hence higher dose. This study provides a baseline data of radioactivity background levels in the Shahpur region of Gulbarga district and will be useful to assess any changes in the radioactive background level due to various man made processes.
is essential for understanding the future changes in natural background radiation of the region, as there are
no earlier results.
2. GEOLOGY OF THE AREA UNDER STUDY
The area under study represents a part of N-E Karnataka, which is well known for granite production and also taking part in iron, manganese and gold ore mining operations. The present work has been carried out in Shahpur region of Gulbarga district of North Karnataka, India. The Shahpur region lies in the North latitude 15° 50' and East longitudes 74° 34'. The study region is rich in granitic rocks which demarcate the Archaean nucleus. A large deposit of uranium has been found in one of the villages Gogi of Shahapur and it is important to study the distribution of radionuclides in the surrounding regions.
3. MATERIALS AND METHODS
Standard procedures were followed for sample collection and preparation, where surface soil over an area 50 cm × 50 cm and 5 cm depth was mixed thoroughly and about 2-3 kg of each sample was collected. The details of the collected samples were noted and then coded. The irst two letters correspond to the type of sample, next two digits correspond to district place (Gulbarga-01), next two correspond to taluk’s place (Shahpur-07) and last two correspond to serial number. These samples were pulverized to a ine powder and then sieved. The samples were then placed for drying at 110°C for 24 hour to ensure that the moisture is completely removed. Each coded pulverized sieved sample was then transferred to a 250 ml cylindrical plastic container. The containers were then weighed and sealed carefully from outside using an adhesive and stored for four to ive weeks to attain secular equilibrium between
226Ra and 222Rn and it's decay products.
The samples were analyzed using a high-resolution gamma spectrometry system. The system comprises of a high purity Ge (HPGe) detector with a relative eficiency of 50% and full width at half maximum (FWHM) of 2 keV for 1.332 MeV γ-ray line of 60Co. The output of the
detector was analyzed using a PC based 8k multichannel analyzer system (GAMMAFAST, Eurosys Mesures). The detector was surrounded by 3” lead shield on all
sides to reduce the background radiations originating
from building materials and cosmic rays (Anilkumar
et al., 2001). Eficiency calibration for the system was
carried out using the standard uranium ore (RGU, IAEA) in geometry available for the sample counting. The samples were counted for a period of 60,000 seconds and the spectra were analyzed for the photo peaks due to radium, thorium daughter products and 40K. The net
count rate under the most prominent photo peaks of
radium and thorium daughter peaks were calculated and the background count rate was subtracted from the respective count rate. Then the activity of the nuclide was calculated from the prominent gamma energies viz., the 226Ra activity was estimated using the 295.1 keV
and 351.9 keV gamma energies emitted by 214Pb and
609.3 keV and 934.0 keV emitted by 214Bi and 186.1 keV
emitted by 226Ra and determination of the activity from
232Th is based on the detection of gamma rays 238.6 keV
from 212Pb, 338.5 keV and 911.2 keV from 228Ac and 583
keV from 208Tl and 1620 keV from 212Bi. The activity of 40K
is based on the detection of it's 1460.8 keV gamma ray. The integral counts under preselected photopeaks were determined by subtracting from the total counts under corresponding photopeaks obtained for the background (taken with an empty container under identical geometry). Then the activity of the nuclide was calculated from the prominent gamma energies using:
Activity (Bq) = (Net area under PP cps × 100 × 100) / (Eficiency (%) × BR (%))
4. RESULTS AND DISCUSSION
The results observed for the 226Ra, 232Th and
40K activity concentrations obtained for each of the
measured sample together with their corresponding total uncertainties are summarized in Table 1. The concentration of thorium, radium and potassium are in the range from 18.46 to 122.4 Bq/kg, 11.75 to 97.5 Bq/kg and 197.8 to 1340 Bq/kg respectively. The mean activity of the three radionuclides was observed to be 38.86 Bq/ kg, 18.94 Bq/kg, and 546.3 Bq/kg respectively for the soil samples and 67.67Bq/kg, 45.28 Bq/kg and 806.6 Bq/ kg for the building material samples of Shahpur region. A correlation was studied between 226Ra and 232Th for
the soil samples of the study region shown in Fig. 1. Radium and thorium activity demonstrated a positive correlation with a coeficient of 0.5733 which is low and predicts a slight geochemical incoherency between the samples collected from Shahpur region. The correlation plots between 226Ra and 232Th for all the building material
samples showed a good positive linear correlation of value 0.9530 (Fig. 2) which predicts that the radium and thorium activity are geologically and geochemically coherent in case of building materials of the study region. A correlation between the granite samples showed a good positive correlation of 0.9984 between three granite samples as in Fig. 3 which shows that radium is intrinsic in country rock at Shahapur and geochemical coherency is maintained.
To assess the radiation hazard, the UNSCEAR (2000) has given the dose conversion factors for converting the activity concentrations of 226Ra, 232Th and
Table 1: Activity, total absorbed gamma dose rate and dose equivalents for the different soil samples
Sample name
Activity Concentration in Bq/Kg Dose rate nGyh-1
Total effective dose µ Svy-1
Annual effective dose equivalent µ Svy-1
232Th 226Ra 40K
Soil
SL010711 26.14±0.7 11.81±0.6 651.1±9.9 48.40±1.1 296.8 237.4 SL010712 29.31±0.7 13.48±0.6 713.2±9.9 53.67±1.5 329.1 263.3 SL010708 56.60±0.6 29.90±0.8 1084±10 93.20±1.1 571.5 457.2 SL010732 35.33±0.6 14.85±0.7 197.8±6.7 36.45±1.3 223.5 178.8 SL010733 37.91±0.6 20.92±0.7 249.4±6.9 42.96±1.0 263.4 210.7 SL010734 41.04±0.6 15.78±0.7 683.4±8.3 60.58±1.0 371.5 297.2 SL010739 48.97±0.7 12.34±1.1 817.8±9.4 69.38±1.3 425.4 340.3 SL010740 18.29±0.5 13.26±0.7 468.0±7.5 36.69±0.9 225.0 150.0 SL010741 49.33±0.8 19.45±0.8 218.6±7.2 47.90±1.1 293.7 235.0 SL010742 48.89±0.7 19.91±0.8 664.9±8.8 66.45±1.1 407.5 326.0 SL010771 26.90±1.5 18.03±1.8 641.1±8.4 51.31±2.1 314.6 251.7 SL010773 38.77±1.8 28.89±1.8 461.5±8.2 56.01±2.3 343.4 274.7 SL010774 47.75±1.7 27.65±1.4 251.2±6.4 52.09±1.9 319.4 255.5
Mean 38.86 18.94 546.3 55.01 337.3 267.5
Building materials
GT010703 110.2±1. 69.92±0.4 1340±14.4 154.7±1.4 978.9 789.1 GT010704 106.6±1.0 52.35±1.1 1322±12.3 143.7±1.6 881.2 705.0 GT010709 121.1±0.4 68.65±0.7 987.3±10.3 146.0±0.9 895.4 716.3 GT010710 117.2±0.9 97.51±0.7 1121±13 162.6±1.4 996.9 797.5 GT010713 122.4±1.4 89.45±1.1 1234±17 166.7±2.1 1022 817.6 GT010714 115.2±2.0 91.25±1.0 1125±14 158.6±2.2 972.8 778.2 SA010715 22.97±0.8 11.75±1.6 569.4±8.1 43.05±1.5 264.0 211.2 SA010716 18.46±0.8 15.42±1.0 687.5±11.7 46.94±1.4 287.8 230.2
SA010717 19.01±0.5 16.14±1.1 705.7±13.1 48.37±1.5 296.6 237.3 SA010718 17.65±0.7 14.57±0.8 667.6±15.7 45.23±1.4 277.3 221.8 BK010705 31.11±0.7 22.12±0.5 249.4±7.0 39.41±1.0 241.7 193.4 BK010706 40.91±0.5 18.32±0.8 220.6±7.2 42.37±1.0 259.8 207.8 BK010707 36.91±0.7 21.22±0.7 256.4±6.1 42.79±1.0 262.4 209.9 BK010708 41.89±0.6 23.92±0.6 275.2±8.5 47.83±1.0 293.3 234.7
Mean 67.67±13.0 45.28±9.3 806.6±113.0 92.03 587.5 453.6
15 20 25 30 35 40 45 50 55 60
10 12 14 16 18 20 22 24 26 28 30 32
226
Ra activity Bq/kg
232
Th activity Bq/kg Correlation between226Ra and232Th activity for soil samples
R = 0.5733
Fig. 1: Correlation between 232Th and 226Ra activity
for Shahapur region soil samples
0 20 40 60 80 100 120 140
0 20 40 60 80 100
226
Ra activity Bq/kg
232
Th activity Bq/kg Correlation between226Ra and232Th activity for building material samples R = 0.9530
Fig. 2: Correlation between 232Th and 226Ra activity for
0.604 and 0.0417 respectively. Using these factors, the total absorbed gamma dose rate in air at 1m above the ground level is calculated by using the formula:
D = (0.604CTh + 0.462CRa + 0.0417CK) nGyh-1
Where, CRa, CTh and CK are the activity concentrations
of Radium, Thorium, and Potassium in the samples in Bq/ kg respectively. It is clearly observed from the Table 1 that the mean gamma absorbed dose rate for soil is 55.01nGy h-1 and 92.03 nGy h-1 for building material
samples. Annual effective dose equivalent received by a member is estimated using a conversion factor of 0.7 SvGy-1, with an outdoor occupancy of 20% assuming
that a person spends about 80% of his time indoors (UNSCEAR, 2000). In the present case the annual effective dose equivalent received from soil and building material samples of Shahapur region is estimated to be 267.5 µ Svy-1 and 453.6 µ Svy-1. It can be observed from
the table that the building material samples especially granite samples show a higher activity hence higher dose which is not ignorable and may pose radiological hazards in due future. The use of these materials for construction purposes has to be given a second thought from radiological point of view. In Table 2 gives the comparison of the activity of radionuclides and dose
rate measured from the study area with the national and international literature values. Our measured values are well within the national and UNSECAR 2000 reported values.
5. CONCLUSION
The results obtained have shown that the total effective dose rate due to natural radioactivity of soil varies from 223 to 572 µSvy-1, which infer that the
radiations are natural background radiations. The present
study shows that the values obtained in the present study are well comparable with the national and international values. Hence the study of natural radiation background of this area is quite constant with other literature values (places) and also over the period of time i.e., these values practically independent of human practices and activities at present. Further work is continued on varieties of the samples in and around of this region (Rajeshwari, 2008 and Nagabhushan, 2009).
6. ACKNOWLEDGEMENTS
The authors are thankful to Dr. D.N. Sharma, Head, RSSD, for his interest in this work and for analysing the samples at their Laboratory. Authors are also grateful to Shri D.A.R. Babu, Head, RMS and TS, RSSD, for his encouragement and support in this work.
7. REFERENCES
Anil Kumar, Narayani Krishnan, S, Sharma, D N, and Abani M C, (2001), Background Spectrum analysis: A method to monitor the performance of a gamma ray spectrometer, Radiation Protection and Environment, 24 (1&2), 195-200
Baranwal V C, Sharma S P, Sengupta D, Sandilya, M K, Bhaumik B K, Guin R and Saha S K, (2006), A new high background radiation area in the Geothermal region of Eastern Ghats Mobile Belt (EGMB) of Orissa, India, Radiation Measurements, 41, 602-610
El-Arabi, A M, (2007), 226Ra, 232Th and 40K concentrations
106 108 110 112 114 116 118
50 60 70 80 90 100
226
Ra activity Bq/kg
232
Th activity Bq/kg Correlation between232
Th and226
Ra activity for granite samples
R= 0.9984
Fig. 3: Correlation between 232Th and 226Ra activity
for Shahapur region granite samples
Table 2: Comparison of the activities of radionuclides and dose rate in soil samples of Shahapur with other literature values of the world
Location 232Th in Bq/kg 226Ra in Bq/kg 40K in Bq/kg Dose rate in nGy h-1 References
Shahapur samples 18–56 12–30 200–1084 36–70 Present work Kalpakkam, tamilnadu 15–776 5–71 200–854 24–556 Kannan et al (2002).
Kaiga: Mean 14.3 33.0 113.7 28.8 Narayana et al (2001) All India 17–158 7–152 43–766 – Kamath et al (1996)
China 1–360 2–690 9–1800 13–760 UNSCEAR (2000)
USA 4–130 4–140 100–700 26–278 UNSCEAR (2000)
in igneous rocks from eastern desert, Egypt and it's radiological implications, Rad. Meas. 42, 94-100.
Kamath, R R, Menon, M R, Shukla, V K, Sadasivan, S, Nambi, K S V, (1996), Natural and fallout radioactivity measurement of Indian soils by gamma spectrometric technique. Fifth National Symposium on Environment, Calcutta, India, Saha institute of Nuclear Physics.
Kannan, V, Rajan, M P, Iyengar, M A R, Ramesh, R, (2002), Distribution of natural and anthropogenic radionuclides in soil and beach sand samples of Kalpakkam (India) using high pure germanium (HPGe) gamma ray spectrometry, Appl. Rad. Isotopes, 57, 109-119.
Nagabhushan N M, (2009), Radiation studies of environmental samples of North Karnataka, India, Ph D Thesis. Gulbarga University, Gulbarga.
Nambi, K S V, Subba Ramu, M C, Eappen, K P, Ramachandran, T V, Murleedharan, T S, Shaik, A N, (1994), A new SSNTD method for the measurement of radon-thoron mixed working levels in dwellings, Bulletin of Radiation Protection 17, 34-35.
Narayana, Y, Somashekarappa, H M, Karunakara, N, Avadhani, D N, Mahesh, H M, Siddappa, K, (2001), Natural Radioacitivity in the soil samples of Coastal Karnataka of South India, Health Physics Society, 80, 24-33.
Rajeshwari T, (2008), Natural Radionuclides Distribution in Soil of Donimalai Region, Sandur of North Karnataka, M Phil Dissertation. Gulbarga University, Gulbarga
UNSCEAR (2000), Sources and Effects of Ionizing Radiation. United Nations Scientiic Committee on the Effect of Atomic Radiation, United Nations, New York.
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