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  • Author or Editor: V. Puranik x
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Abstract  

In this study, an accurate faster gamma spectrometry method for measuring the low level activity concentrations of 137Cs using in situ pre-concentration technique on copper ferrocyanide cartridge was standardized. Due to unavailability of reference standard in the copper ferrocyanide matrix, efficiency calibration curves were plotted using RGU and RGTh reference standards. To harmonize the difference in density of standard and sample the required density correction factors for photo peak efficiency were generated. The in situ pre-concentration technique followed by gamma-ray spectrometry was applied for activity determination in surface seawater from eight locations in the coastal marine environment of Arabian Sea. The mean activity concentration of 137Cs ranged between 0.71 and 0.91 Bq/m3. Higher activity concentrations were observed at location with latitude, longitude of 21.6°N, 69.57°E as compared to concentration observed at location with latitude, longitude 16.98°N, 73.25°E. The observed concentrations were found to be in range of data reported in Asia–Pacific Marine radioactive database (ASPARMARD). The results will fill up the gaps in the existing database. The generated data will be useful for monitoring fresh input of anthropogenic radionuclide into coastal marine environment for post Fukushima environmental assessment.

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This paper discusses the measurement of naturally occurring radioactivity materials (NORM) in beach sand minerals using high resolution gamma spectrometry. In India, the beach sand minerals of economic interest from coastal Kerala, Tamil Nadu and Orissa are enriched with NORM due to the occurrence of monazite deposits and heavy minerals such as zircon, ilmenite, magnetite, garnet, rutile etc. Since many of these ores are rich in 232Th and other radio elements, certification of radioactivity levels has become mandatory in recent years. The average activity concentrations of 226Ra in zircon, rutile and garnet were 3,531, 1,134 and 17 Bq kg−1, respectively. The average activity concentration of 232Th observed in zircon, rutile and garnet were 618, 454 and 64 Bq kg−1, respectively. Concentration of 226Ra, 232Th, and 40K in ilmenite ore ranged from 17.6–444 Bq kg−1, 80.4–1971 Bq kg−1 and ≤5.5–25.0 Bq kg−1, respectively.

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Coarse and fine fractions of particulate matter (PM) were collected and analysed for trace elements using Instrumental Neutron Activation Analysis and Energy Dispersive X-ray Fluorescence techniques. The result showed high concentrations of Fe, S, Zn and Pb in both the size fractions. The elemental data obtained is used to analyze the temporal and seasonal variations. The trend showed maximum concentrations of PM and metals during winter and minimum during the monsoon season. Enrichment Factor (EF) and source analysis was performed for the same data set to identify the strength of contribution of anthropogenic sources and the possible contributing sources in the study area. EF studies showed high enrichments of Zn, Pb and As in the fine fraction particles. Crustal, vehicular and industrial emissions are identified as the major contributing sources of PM in the study area.

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Comprehensive quality assurance/quality control procedure is very much necessary to obtain accurate and precise analytical measurement result. This paper discusses the quality control aspects of the High-Purity Germanium (HPGe) based gamma spectrometry system, which has been used for the measurement of low-level radioactivity in environmental samples. The gamma spectrometry system consisting of coaxial n-type HPGe detector having 50% relative efficiency with respect to 7.62 cm x 7.62 cm NaI (Tl), Nuclear Instrumentation Module (NIM) based pulse processing electronic accessories and 8 k MCA. To reduce the background contribution, 7.5 cm thick lead has been placed surrounding the detector. The minimum detectable activities (MDA) with 95% confidence level (for 300 g soil sample and 100,000 s counting time) for important radionuclides such as 238U, 226Ra, 232Th, 40K, and 137Cs are 10.4, 4.3, 4.1, 16.9 and 0.1 Bq kg−1, respectively. The Quality control (X bar R) charts were plotted using 137Cs and 40K background counts observed periodically, which showed that the fluctuation is well within the confidence limit and confirms the stability of the system. The laboratory has been participating in the proficiency tests (PTs) of the International Atomic Energy Agency (IAEA). In recently concluded PTs, the samples include soil, spiked standard solution, spinach, phosphogypsum and spiked air filter were analysed for the natural, fission and activation products radionuclides. The performance evaluation of the IAEA PTs showed that the laboratory results were in good agreement with the target value, which confirms the reliability and traceability of the gamma spectrometric measurement result of the laboratory.

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Abstract  

An investigation on the distribution of radium activity levels in the entire south eastern coast of Tamil Nadu, India, from Chennai to Kanyakumari was carried out. Insitu preconcentration technique was adopted by passing 1,000 L of seawater through MnO2 impregnated cartridge filters at all the locations. In the coastal waters, 226Ra and 228Ra concentration was observed to be in the range of 1 to 1.81 and 3.1 to 7.5 mBq/L, respectively with an average of 1.52 and 4.53 mBq/L. respectively, while the sediment samples showed 226Ra activity levels from 8.1 to 129.0 Bq/kg and 228Ra varied from 14.7 to 430.01 Bq/kg. The Kd values for 226Ra was observed to be from 5.3E03 to 3.5E05 L/kg and for 228Ra it was in the range of 2.3E03 to 5.9E04. It was observed that the concentration of 228Ra was more than 226Ra in all the locations. The spatial distribution of the activity with respect to location is discussed in the paper. The radioactive database obtained, represents reference values for coastal environment of Tamil Nadu.

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The study summarizes radiological characteristics of Banduhurang open cast mine which includes qualitative and quantitative behavior of 222Rn concentration, external gamma radiation level over the mine pit as well as in its adjoining environment, long-lived alpha (LLα) activity concentration associated with the respirable size of ore dust and assessment of dose to the mine workers in 2006–2008. The investigations reveal that geometric means (χg) of measured radon concentration were 36.39, 38.69, 26.64 and 24 Bq m−3 with respective geometric standard deviations (σg) were 1.52, 1.55, 1.36 and 1.68 Bq m−3 and χg of gamma absorbed dose rates were 0.54, 0.64, 0. 45 and 0.15 μGy h−1 with respective σg were 1.63, 1.53, 1.52 and 1.72 μGy h−1 over the mine pit, ore yard, waste yard and in the surrounding environment within a 10 km radius to the mine, respectively. The χg of LLα activity was observed to be 16 mBq m−3 with σg of 1.9 mBq m−3. The annual mean effective dose equivalent received by the member radiation workers of Banduhurang mine was estimated to 1.41 mSv y−1, which is about 7% of the prescribed dose limits of 20 mSv y−1.

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A brief study on dissolved radionuclides in aquatic environment, especially in ground water, constitutes the key aspect for assessment and control of natural exposure. In the present study the distribution of natural uranium and 226Ra concentration were measured in ground water samples collected within a 10 km radius around the Narwapahar uranium mine in the Singhbhum thrust belt of Jharkhand, India in 2007–2008. The natural uranium content in the ground water samples in this region was found to vary from 0.1 to 3.75 μg L−1 with an average of 0.87 ± 0.73 μg L−1 and 226Ra concentration was found to vary from 5.2 to 38.1 mBq L−1 with an average of 13.73 ± 7.34 mBq L−1. The mean annual ingestion dose due to intake of natural uranium and 226Ra through drinking water pathway to male and female adults population was estimated to be 6.55 and 4.78 μSv y−1, respectively, which constitutes merely a small fraction of the reference dose level of 100 μSv y−1 as recommended by WHO.

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This paper presents the results of measurement of natural and fallout radioactivity in soil samples of Chamba and Dharamshala areas in Himachal Pradesh, India. Spatial distribution of 238U, 226Ra, 232Th, 40K, 137Cs was determined using High resolution gamma-ray spectrometry. The mean activity concentration in Chamba region due to 238U, 232Th, 40K and 137Cs was 32.3, 58.4, 588.3, and 10.9 Bq kg−1, respectively, whereas in Dharamshala it was 35.7, 61.3, 594.9, 10.0 Bq kg−1, respectively. Absorbed gamma dose rate (D) in air was calculated using appropriate dose conversion factors, which was varying from 45 to 103 nGy h−1. To control the radiation exposure due to natural radioactivity in soil, if it is used as building materials, radium equivalent activity (Raeq) and activity index were also evaluated. Radium equivalent activity calculated for the soil ranged from 95.5 to 234.2 Bq kg−1 with average of 171.0 Bq kg−1.The calculated Activity concentration index was ranged from 0.34 to 0.85 with an average value of 0.64. The natural and fallout radioactivity in soil of this region is comparable with Indian average and other parts of the world. The percentage contribution of 238U, 232Th and 40K and 137Cs to the average external gamma dose rate was 22, 46, 32, 2%, respectively. This shows that the dose contribution due to fallout radioactivity is negligible as compared to the natural radioactivity.

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In order to understand the mobility of uranium it is very important to know about its sorption kinetics and the thermodynamics behind the sorption process on soil. In the present study the sorption kinetics of uranium was studied in soil and the influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficient of uranium on soil was measured by laboratory batch method. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models. The sorption energy for uranium from the D–R adsorption isotherm was calculated to be 7.07 kJ mol−1.The values of ΔH and ΔS were calculated to be 37.33 kJ mol−1 and 162 J K−1 mol−1, respectively. ΔG at 30 °C was estimated to be −11.76 kJ mol−1. From sorption kinetics of uranium the reaction rate was calculated to be 1.6 × 10−3 min−1.

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“In-House” resin Polyacrylhydroxamic acid (PHOA) has been synthesized and utilized targeting ground water remediation; recovery of uranium from low concentration aqueous solution e.g., mining activities related water, flooding of excavated or deplumed areas, nuclear plant washed effluent and process generated effluents in nuclear plant during front-end as well as back-end treatment. In the present study, treatment of field effluent containing heavy metals and radio-nuclides from contaminated mining sites reflected preference for uranium with respect to manganese. The specific complexation between the extractant and metal ion especially uranium provides high distribution co-efficient (K d) for uranium (K d,U = 1,450 mL/g from inlet of Effluent Treatment Plant (ETP) and K d,U = 74,950 mL/g for synthetic solution) compared to high level impurity (1,000 times higher concentration) of manganese (K d,Mn = 111 mL/g from inlet of ETP and K d,Mn = 10,588 mL/g for synthetic solution). The “In-House” resin showed significant extractability (70–95% elution efficiency) and indicates a possibility of selective removal/recovery of the valuable metal ions even from secondary sources. As a specialty, resin can be regenerated and reused.

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