Gamma-ray measurements in terrestrial/environmental samples require the use of high efficient detectors because of the low level of the radionuclide activity concentrations in the samples; thus ...scintillators are suitable for this purpose. Two scintillation detectors were studied in this work; CsI(Tl) and NaI(Tl) with identical size for measurement of terrestrial samples for performance study.
This work describes a Monte Carlo method for making the full-energy efficiency calibration curves for both detectors using gamma-ray energies associated with the decay of naturally occurring radionuclides
137Cs (661
keV),
40K (1460
keV),
238U (
214Bi, 1764
keV) and
232Th (
208Tl, 2614
keV), which are found in terrestrial samples. The magnitude of the coincidence summing effect occurring for the 2614
keV emission of
208Tl is assessed by simulation.
The method provides an efficient tool to make the full-energy efficiency calibration curve for scintillation detectors for any samples geometry and volume in order to determine accurate activity concentrations in terrestrial samples.
► CsI (Tl) and NaI (Tl) detectors were studied for themeasurement of terrestrial samples. ► Monte Carlo method was used for efficiency calibration using natural gamma emitting terrestrial radionuclides. ► The coincidence summing effect occurring for the 2614 keV emission of
208Tl is assessed by simulation.
•Gamma dose rate was measured around a region indentified as prospective uranium mining area.•Dose was evaluated by GM based survey meter, TLDs, and analyses of soil samples for radionuclides.•Dose ...evaluated from radionuclide activities is an underestimation when compared to in situ measurement.•In situ measurement of dose by survey meter accounts for non-uniform distribution of radionuclides.
Indoor and outdoor gamma dose rates were evaluated around a prospective uranium mining region – Gogi, South India through (i) direct measurements using a GM based gamma dose survey meter, (ii) integrated measurement days using CaSO4:Dy based thermo luminescent dosimeters (TLDs), and (iii) analyses of 273 soil samples for 226Ra, 232Th, and 40K activity concentration using HPGe gamma spectrometry. The geometric mean values of indoor and outdoor gamma dose rates were 104nGyh−1 and 97nGyh−1, respectively with an indoor to outdoor dose ratio of 1.09. The gamma dose rates and activity concentrations of 226Ra, 232Th, and 40K varied significantly within a small area due to the highly localized mineralization of the elements. Correlation study showed that the dose estimated from the soil radioactivity is better correlated with that measured directly using the portable survey meter, when compared to that obtained from TLDs. This study showed that in a region having localized mineralization in situ measurements using dose survey meter provide better representative values of gamma dose rates.
Exposure due to thoron (220Rn) gas and its decay products in a thorium fuel cycle facility handling thorium or 232U/233U mixture compounds is an important issue of radiological concern requiring ...control and mitigation. Adsorption in a flow-through charcoal bed offers an excellent method of alleviating the release of 220Rn into occupational and public domain. In this paper, we present the design, development, and characterization of a Thoron Mitigation System (TMS) for industrial application. Systematic experiments were conducted in the TMS for examining the 220Rn mitigation characteristics with respect to a host of parameters such as flow rate, pressure drop, charcoal grain size, charcoal mass and bed depth, water content, and heat of the carrier gas. An analysis of the experimental data shows that 220Rn attenuation in a flow through charcoal bed is not exponential with respect to the residence time, L/Ua (L: bed depth; Ua: superficial velocity), but follows a power law behaviour, which can be attributed to the occurrence of large voids due to wall channeling in a flow through bed. The study demonstrates the regeneration of charcoal adsorption capacity degraded due to moisture adsorption, by hot air blowing technique. It is found that the mitigation factor (MF), which is the ratio of the inlet 220Rn concentration (Cin) to the outlet 220Rn concentration (Cout), of more than 104 for the TMS is easily achievable during continuous operation (>1000 h) at a flow rate of 40 L min−1 with negligible (<1 cm of water column) pressure drop. The Thoron Mitigation System based on adsorption on charcoal bed offers a compact and effective device to remove 220Rn from affluent air streams in a space constrained domain. The prototype system has been installed in a thorium fuel cycle facility where it is being evaluated for its long-term performance and overall effectiveness in mitigating 220Rn levels in the workplace.
•A prototype charcoal based 220Rn mitigation system is developed and characterized.•220Rn attenuation in charcoal bed is not exponential, but follows power law behaviour.•Persistent mitigation factor of ∼104 was achieved for ∼1000 h operation of the system.•Prototype system can be scaled up for applications in thorium processing facilities.
Air-to-grass mass interception factors for radionuclide are important basic input parameter for the estimation of radiation dose to the public around a nuclear power plant. In this paper, we present ...the determination of air-to- grass mass interception factors for iodine using a 2 m × 2 m × 2 m (l × b × h) size environmental chamber. The temperature, humidity, and rainfall inside the environmental chamber was controlled to required values to simulate different environmental conditions. Grass (Pennisetum purpureum, Schum), grown in pots, was kept inside the environmental chamber and stable iodine in elemental form was sublimed quickly inside the chamber to simulate an accidental release of iodine to the environment. The concentration of iodine in the air was measured periodically by drawing air through a bubbling setup, containing 1% sodium carbonate solution. The mass interception factor for dry deposition varied in the range of 0.25–7.7 m2 kg−1 with mean value of 2.2 m2 kg−1 with respect to fresh weight of grass, and that due to wet deposition varied in the range of 0.6–4.8 m2 kg−1 with mean value of 2.3 m2 kg−1. The mass interception factor was inversely correlated with the total iodine deposited through dry deposition as well as with the rainfall.
•Mass interception factor of iodine for grass was estimated by chamber experiments.•Mean value of mass interception factor for dry depositions was 2.2 m2 kg−1.•Mean value of mass interception factor for wet deposition was 2.3 m2 kg−1.•Mass interception factor was inversely correlated with the total iodine deposited.•Mass interception factor was inversely correlated with total rainfall.
Regulating the environmental discharge of 220Rn (historically known as thoron) and its decay products from thorium processing facilities is important for protection of environment and general public ...living in the vicinities. Activated charcoal provides an effective solution to this problem because of its high adsorption capacity to gaseous element like radon. In order to design and develop a charcoal based Thoron Mitigation System, a mathematical model has been developed in the present work for studying the 220Rn transport and adsorption in a flow through charcoal bed and estimating the 220Rn mitigation factor (MF) as a function of system and operating parameters. The model accounts for inter- and intra-grain diffusion, advection, radioactive decay and adsorption processes. Also, the effects of large void fluctuation and wall channeling on the mitigation factor have been included through a statistical model. Closed form solution has been provided for the MF in terms of adsorption coefficient, system dimensions, grain size, flow rate and void fluctuation exponent. It is shown that the delay effects due to intra grain diffusion plays a significant role thereby rendering external equilibrium assumptions unsuitable. Also, the application of the statistical model clearly demonstrates the transition from the exponential MF to a power-law form and shows how the occurrence of channels with low probability can lower mitigation factor by several orders of magnitude. As a part of aiding design, the model is further extended to optimise the bed dimensions in respect of pressure drop and MF. The application of the results for the design and development of a practically useful charcoal bed is discussed.
•Models are developed for describing 220Rn adsorption and transport in charcoal bed.•Dependence of mitigation factor on system parameters and flow rate is established.•Flow channelling and voidage fluctuation effects on 220Rn adsorption are discussed.•Transition from exponential to Power-law forms of variation is presented.•Optimization method for bed dimension for specified mitigation factor is presented.
Detailed studies were carried out to establish site-specific soil to grass transfer factors (Fv) and grass to cow milk transfer coefficients (Fm) for radioactive cesium (137Cs) and stable cesium (Cs) ...for Kaiga region, where a nuclear power station has been in operation for more than 10 years. The study included adopted cows, cows of local farmers, and cows from the dairy farm. A grass field was developed specifically for the study and 2 local breed cows were adopted and allowed to graze in this grass field. The soil and grass samples were collected regularly from this field and analyzed for the concentrations of 137Cs and stable Cs to evaluate the soil to grass Fv values. The milk samples from the adopted cows were analyzed for the 137Cs and stable Cs concentrations to evaluate Fm values. For comparison, studies were also carried out in dominant grazing areas in different villages around the nuclear power plant and the cows of local farmers which graze in these areas were identified and milk samples were collected and analyzed regularly. The geometric mean values of Fv were found to be 1.1 × 10−1 and 1.8 × 10−1 for 137Cs and stable Cs, respectively. The Fm of 137Cs had geometric mean values of 1.9 × 10−2 d L−1 and 4.6 × 10−2 d L−1, respectively, for adopted Cows 1 and 2; 1.7 × 10−2 d L−1 for the cows of local farmers, and 4.0 × 10−3 d L−1 for the dairy farm cows. The geometric mean values of Fm for stable Cs were similar to those of 137Cs. The Fm value for the dairy farm cows was an order of magnitude lower than those for local breed cows. The Fm values observed for the local breed cows were also an order of magnitude higher when compared to the many values reported in the literature and in the IAEA publication. Possible reasons for this higher Fm values were identified. The correlation between Fv and Fm values for 137Cs and stable Cs and their dependence on the potassium content (40K and stable K) in the soil and grass were also studied. In order to estimate the ingestion dose accurate data of the dietary habits of the population was necessary and this data was collected through a well planned demographic survey. The internal doses to a child due to the ingestion of 137Cs along with the milk of the local cows and from the dairy farm were found to be 0.29 μSv y−1 and 0.04 μSv y−1,while that to an adult were 0.39 μSv y−1 and 0.05 μSv y−1, respectively.
•This is a detailed study on Fv and Fm for 137Cs and stable Cs around the Kaiga nuclear power plant, India.•The geometric mean values of Fv were found to be 1.1 × 10−1 and 1.8 × 10−1 for 137Cs and stable Cs, respectively.•The Fm value for 137Cs for the local breed cows was estimated to be 2.4 × 10−2 d L−1.•The Fm value for dairy farm cows (4.0 × 10−3 d L−1) was an order of magnitude lower than those for local breed cows.•The reasons for the higher Fm values for 137Cs for the local breed cows are identified.
Studies on concentrations of primordial radionuclides in soil samples of Botswana were carried out. Measurements were made by gamma spectrometry employing a 41% relative efficiency HPGe detector. The ...activity of
226Ra was found to vary in the range 6.1–97.4
Bq
kg
−1 with a mean value of 34.8
Bq
kg
−1,
232Th in 7.4–110.0
Bq
kg
−1 with a mean value of 41.8
Bq
kg
−1 and that of
40K between 33.5 and 1085.7
Bq
kg
−1 with a mean value of 432.7
Bq
kg
−1 in surface soils. Existence of strong correlations in the distributions of these radionuclides indicates that an individual result for any one of the radionuclide is a good predictor of the concentration of the other. The mean value of effective dose, due to the
238U series,
232Th series and
40K in soil, was 0.07
mSV. The results of the present study are compared with the literature values reported for other normal background regions of the world and discussed.
A study on absorption of radon by different edible oils of plant origins produced and used in India was conducted in order to identify efficient radon-absorbing oils. A comparative study of radon ...absorption by edible oils of India with that of olive oil, which is known as a good absorber of radon, was also carried out. The study was performed by bubbling known concentrations of radon through the oil contained in a bottle and then evaluating the bubbled oil by gamma-ray spectrometry using an HPGe detector. The results show that oils such as coconut oil, gingelly oil (till oil), ground nut oil, mustard oil, sunflower oil, and saffola kardi oil are also good absorbers for radon, and among them coconut oil and gingelly oils are better absorbers than olive oil. The Henry's equilibrium constant (or the concentration factor), an indicator for the solubility of gas in liquids, was also measured for different types of oil by saturating a known volume of the oil with radon. The Henry's equilibrium constant varied in the range 7.32-8.22 for the Indian vegetable oils, and for olive oil it was found to be 7.88. The details of the experimental technique employed and results obtained are presented and discussed in this paper.
The outdoor and indoor environmental gamma dose rates in air have been measured in several parts of Udupi district, Karnataka, India using thermoluminescent dosimeters (TLDs). The outdoor annual ...gamma dose values varies in the range 0.49–1.17 mGy/year with mean 0.75 ± 0.18 mGy/year. Similarly indoor annual gamma dose varies in the range 0.51–1.10 mGy/year with mean 0.74 ± 0.13 mGy/year. The mean values of indoor and outdoor gamma dose rates were 84 and 86 nGy/h respectively with indoor to outdoor dose ratio of 1.02.
Measurements of radon concentration in soil gas have been carried out using a bubbling system in which the soil gas is drawn through an active pumping to bubble a liquid absorber (olive oil) for the ...deposition of the soil gas in it. After the bubbling process, the absorber is then taken for gamma-ray measurements. Gamma-ray photopeaks from the
214Pb and the
214Bi radon progeny are considered for the detection of the
222Rn gas to study the concentration levels for radon soil gas. Results for some field measurements were obtained and compared with results obtained using AlphaGuard radon gas monitor. The technique provides a possible approach for the measurements of radon soil gas with gamma-ray spectrometry.
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