MODELING AND EXPERIMENTS TO ESTIMATE RADON EMANATION FACTOR IN SOIL-GRAIN SIZE AND MOISTURE EFFECT

The influence of soil grain size on its radon emanation mechanism was investigated by developing a Monte-Carlo model. The proposed model supplements the previous formulations by accounting for the effect elicited by specific surface area of the sample. The specific surface area of a sample is governed by its grain size and it strongly influences the emanation rate which is a surface phenomenon. The emanation study was further extended to include the moisture effect. Experiments were carried out with two soil samples; Soil-2 and Soil-4 collected from different terrains, to analyze the role played by moisture in the emanation mechanism. The above model was augmented with provisions to include the moisture input. The model could reproduce the experimental results. There is an abrupt increase in the emanation factor when the moisture content changes from 0 to 2%. Thereafter, the increase is gradual and finally becomes steady when the moisture level reaches 10%. Soil-2 and Soil-4 showed sizeable difference in their radon emanation factor values. This could be explained based on the parent226Ra distribution pattern which stems from the mineralogical composition of the samples. Quartz was predominantly found in Soil-2, whereas Soil-4 shows peaks corresponding to minerals namely ilmenite, Rutile and Zircon confirming relatively higher concentration of heavy minerals than Soil-2. The emanation factor values of the individual minerals reported in the literature were used to decide upon the 226Ra distribution depth and with this input the model to ascertain the experimental observations.

Exposure of patients to low doses of X-radiation during neuro-interventional imaging and procedures: Dose estimation and analysis of γ-H2AX foci and gene expression in blood lymphocytes

Radiation has widespread applications in medicine. However, despite the benefits of medical radiation exposures, adverse long-term health effects are cause for concern. Protein and gene biomarkers are early indicators of cellular response after low-dose exposure. We examined DNA damage by quantifying γ-H2AX foci and expression of twelve candidate genes in the blood lymphocytes of patients exposed to low doses of X-radiation during neuro-interventional procedures. Entrance surface dose (ESD; 10.92-1062.55 mGy) was measured by thermoluminescence dosimetry (TLD). Absorbed dose was estimated using γ-H2AX focus frequency and gene expression, with in vitro dose-response curves generated for the same biomarkers. γ-H2AX foci in post-exposure samples were significantly higher than in pre-exposure samples. Among the genes analysed, FDXR, ATM, BCL2, MDM2, TNFSF9, and PCNA showed increased expression; CDKN1A, DDB2, SESN1, BAX, and TNFRSF10B showed unchanged or decreased expression. Absorbed dose, estimated based on γ-H2AX focus frequency and gene expression changes, did not show any correlation with measured ESD. Patients undergoing interventional procedures receive considerable radiation doses, resulting in DNA damage and altered gene expression. Medical procedures should be carried out using the lowest radiation doses possible without compromising treatment.

QUANTIFICATION OF BACK DIFFUSION IN RADON AND THORON EXHALATION RATE MEASUREMENTS

The radon (222Rn) and thoron (220Rn) fluxes from the soil and building materials are the major contributors to their indoor levels. Hence, the measurement of radon and thoron exhalation rates from the source matrix becomes the foremost step in controlling the indoor radon and thoron exposure. It is a challenge to measure the exhalation rates without disturbing the natural conditions. The back-diffusion phenomenon modifies the exhalation rate. The work presented here is to measure the back-diffusion coefficient and takes it into consideration while estimating the exhalation rate. For radon measurements, the back-diffusion coefficient and the free exhalation rates were simultaneously estimated by adopting a novel methodology. The leak rate of the experimental setup measured by this methodology was agreeable with the value measured by adopting the standard technique. In the case of thoron, the back-diffusion effect was found to be negligible for the present experimental conditions and it is duly explained. The above results were obtained by analyzing two soil samples with high 238U and 232Th content collected from monazite-rich coastal area.

Optimization of 14C LSC measurement using CO2 absorption technique

Liquid Scintillation Counting (LSC) is the most commonly used technique for quantification of 14C in the environmental samples. An optimization study was carried out for the analysis of 14C with the direct carbon dioxide absorption method using LSC. The absorption capacity of CO2 in varying amounts of CO2 absorber Carbo-Sorb E to Permafluor scintillation cocktail volumes is found to be 5.33 ± 0.053 mmol/mL of Carbo-Sorb E. The optimum volume ratio of Carbo-Sorb E to Permafluor scintillation cocktail is found to be 1:1 based on the minimum detection activity (MDA) values. The effect of CO2 loading in the optimized absorption mixture shows that with an increasing CO2 amount (up to saturation) there is an increase in tSIE values which is due to an increase of Compton scattering effect in the CO2 loaded samples. The region of interest (ROI) for 14C measurement is found to be 10–96 keV based on the figure of merit values and the efficiency for detecting 14C is 83.45 % in the optimized ROI window.

Studies on pelletised lithium magnesium borate TL material for eye lens dosimetry

Recent epidemiological studies in various cohorts confirm that radiation induced cataract may occur at a threshold dose as low as 0.5 Gy. ICRP has recognised the higher radiosensitivity of eye lens and recommended to reduce annual eye lens dose limit from 150 to 20 mSv. Present dosimetry for eye lens is largely based on LiF based dosimeters. The present work is an attempt towards using near tissue equivalent lithium borate material namely lithium magnesium borate doped with terbium (LMB:Tb) in eye lens dosimetry. The material in powder form was synthesised using solid state sintering method and pelletised using poly tetra fluoro ethylene (PTFE) as binding agent. It was observed that 130 mg of 1 mm thick LMB:Tb pellet bound with PTFE showed stable glow curve structure and attractive dosimetric features in terms of sensitivity, fading, linearity, reusability etc. A proposal of 1.5 mm Teflon encapsulation corresponding to tissue equivalent thickness of 3 mm was put forward for an ideal dosimeter for the measurement in terms of H_p(3). Energy and angular dependence studies based on FLUKA simulations suggest a flat response for the prototype design. In addition to PTFE, various tissue equivalent encapsulations such as polyimide, polyamide 6 and PMMA were also evaluated using FLUKA code.

Soil radioactivity measurements and estimation of radon/thoron exhalation rate in soil samples from Kalpakkam residential complex

The objective of this study is to compute the primordial radionuclides activity in soil samples and estimate the radon/thoron exhalation rates. A total of 25 locations were chosen for the study at Kalpakkam. Ambient radiation levels were monitored prior to collection of samples, which were subjected to gamma spectrometry. While (238)U concentration was found to be below detectable limit, the activities of (232)Th and (40)K were varying from 34.53 to 1093.11 Bq kg(-1) and 36.6 to 570.08 Bq kg(-1), respectively. The radium equivalent activities (Raeq) were in the range of 83-1574 Bq kg(-1). There was no appreciable radon exhalation, and the thoron surface exhalation rate varied from 942 to 7720 Bq m(-2) h(-1). The annual effective dose was ranging from 0.05 to 0.81 mSv y(-1). Good correlation was observed between (232)Th content and thoron exhalation rate. The details of the study are presented in this article.

Radiation-induced defects in manganese-doped lithium tetraborate phosphor

Lithium tetraborate doped with manganese synthesised by solid-state sintering technique exhibits a dosimetric peak at 280°C. The high-temperature glow curve results in no fading for three months. The sensitivity of Li2B4O7:Mn is determined to be 0.9 times that of TLD-100. The infrared spectrum of this phosphor indicates the presence of bond vibrations corresponding to BO4 tetrahedral and BO3 triangles. The mechanism for thermoluminescence in this phosphor was proposed based on the thermoluminescence (TL) emission spectra, kinetic analysis of TL glow curves and electron paramagnetic resonance (EPR) measurements on non-irradiated and gamma-irradiated phosphors. It was identified that oxygen vacancies and Boron oxygen hole centre (BOHC) are the electron and hole trap centres for TL in this phosphor. When the phosphor is heated, the electrons are released from the electron trap and recombine with the trapped holes. The excitation energy during the recombination is transferred to the nearby Mn(2+) ions, which emit light at 580 nm.

Prediction of background in low-energy spectrum of Phoswich detector

In vivo monitoring of actinides in occupational workers is done using Phoswich detector by measuring the low-energy X ray and gamma rays. Quantification of actinides like plutonium and americium in the lungs is extremely difficult due to higher background in the low-energy regions, which is from ambient background as well as from the subject. In the latter case, it is mainly due to the Compton scattering of body potassium, which varies person-to-person. Hence, an accurate prediction of subject-specific background counts in the lower-energy regions is an essential element in the in vivo measurement of plutonium and americium. Empirical equations are established for the prediction of background count rate in (239)Pu and (241)Am lower-energy regions, called 'target regions', as a function of count rate in the monitoring region (97-130 keV)/(40)K region in the high-energy spectrum, weight-to-height ratio of the subject (scattering parameter) and the gender.

Function of minerals in the natural radioactivity level of Vaigai River sediments, Tamilnadu, India--spectroscopical approach

Using Gamma ray and Fourier Transform Infrared (FTIR) spectroscopic techniques, level of natural radioactivity ((238)U, (232)Th and (40)K) and mineralogical characterization of Vaigai River sediments have been analyzed with the view of evaluating the radiation risk and its relation to available minerals. Different radiological parameters are calculated to know the entire radiological characterization. The average of activity concentrations and all radiological parameters are lower than the recommended safety limit. However, some sites are having higher radioactivity values than the safety limit. From the FTIR spectroscopic technique, the minerals such as quartz, microcline feldspar, orthoclase feldspar, kaolinite, gibbsite, calcite, montmorillonite and organic carbon are identified and they are characterized. The extinction co-efficient values are calculated to know the relative distribution of major minerals such as quartz, microcline feldspar, orthoclase feldspar and kaolinite. The calculated values indicate that the amount of quartz is higher than orthoclase feldspar, microcline feldspar and much higher than kaolinite. Crystallinity index is calculated to know the crystalline nature of quartz and the result indicates that the presence of ordered crystalline quartz in the present sediment. The role of minerals in the level of radioactivity is assessed by multivariate statistical analysis (Pearson's correlation and Cluster analysis). The statistical analysis confirms that the clay mineral kaolinite is the major factor than other major minerals to induce the important radioactivity variables such as absorbed dose rate and concentrations of (232)Th and (238)U.

Role of sediment characteristics on natural radiation level of the Vaigai river sediment, Tamilnadu, India

The sediment characteristics such as granulometric contents (sand, silt and clay), organic matter, magnetic susceptibility (low and high frequency) and weight percentage of magnetic minerals and the natural radionuclide ((238)U, (232)Th and (40)K) contents have been analyzed for the sediment samples of Vaigai river with an aim of evaluating the radiation hazard nature and assessing characterization of sediment. Granulometric analysis confirmed that the sand is major content. The organic matter content is ranged from 0.30 to 8.62% and comparison shows that the present river has high organic content. The magnetic measurement results indicated that the sites S16, S18 and S25 may be affected anthropogenically. Frequency dependence magnetic susceptibility is calculated to know the contribution of grains to magnetic susceptibility. Average of activity concentrations (except (40)K) and all calculated radiological parameters are within the recommended level. Multivariate statistical analyses (Pearson correlation, cluster and factor analysis) dictated that the role of sediment characteristics on the level of radioactivity in the river sediments. The content of organic matter and clay, and magnetic parameters are positively correlated with important radioactive variables. The measurement of organic matter and magnetic susceptibility in various granulometric contents show some higher values in silt and clay fractions. Radioactivity level was also measured for the samples (after removing silt and clay fractions from bulk samples) and the results show decrease in radioactive variables. The present study stated that the lower grain sized fractions have the ability to absorb the contents such as organic content and magnetic minerals as cations on their surface and raise the level of radioactivity. Percentage of decrease in the natural radionuclides of (238)U, (232)Th, (40)K and absorbed dose rate of the samples (after removing the silt and clay fractions from bulk samples) to the bulk samples are 13.59, 33.37, 20.52 and 26.13% respectively. Thus, it is concluded that the radiation effect does not pose to the public those who are using these sediments.

Synthesis and characterisation of BaSo4:Eu thermoluminescence phosphor

Polycrystalline powder samples of BaSO(4) doped with Eu(2+) were prepared by solid-state reaction in different reducing atmospheres. Photoluminescence (PL), thermoluminescence (TL), TL kinetic and dosimetric studies have been carried out in this phosphor. The TL glow curve of BaSO(4):Eu(2+) showed only a single peak at 513 K unlike other phosphors and the TL intensity is about three to four times higher than that of CaSO(4):Dy, which is currently used as the radiation dosemeter for personnel monitoring in India. The TL dose response of the phosphor was found to be linear up to the dose range of 10(3) Gy beyond which saturation sets in. PL and TL spectra showed the characteristic emission of Eu(2+) ion. The TL parameters such as trap depth (E) or the energy required to release the electron or hole from the trap, frequency factor (s) and the order of kinetics (b) are determined by different methods such as isothermal decay, initial rise and variable heating rate.

High-sensitive CaSO4:Dy thermoluminescent phosphor synthesis by co-precipitation technique

This paper describes the successful development of the co-precipitation technique for the preparation of a high-sensitive dysprosium-doped calcium sulphate (CaSO(4):Dy) thermoluminescent dosimetry (TLD) phosphor with dosimetric glow peak at approximately 230 degrees C which is a desired development in the field of radiation protection dosimetry. The main advantages of this co-precipitation technique over the conventional recrystallisation technique of phosphor preparation are: (i) preparation time is very less; (ii) quantity of sulphuric acid evaporated is insignificant; (iii) higher TL sensitivity -20% more than the present material; (iv) better glow curve structure; (v) lesser glow peak shift and better linearity to gamma and (vi) uniform crystal morphology and lower grain size-all grains are mostly cuboidal in shape, quite uniform and small (average size about 25 microm), suitable for manufacturing teflon discs in as-prepared form. Optimum values of various parameters in the method of preparation for a batch of 20 g CaSO(4):Dy phosphors to obtain maximum TL sensitivity, with favourable glow curves are studied.

Gamma dose measurement in dwellings of Agastheeswaram Taluk of Kanyakumari district, lying 30 km radius from Kudankulam nuclear power plant site

Most of the building materials contain naturally occurring radioactive elements, the most important of which are potassium (40)K and the members of two natural radioactive series, which can be represented by the isotopes of thorium (232)Th and Uranium (238)U. The presence of these radioisotopes in the materials causes external exposure to the people who live in the building. In addition, the disintegration of Uranium (238)U increases the concentration of radon gas (222)Rn and of its daughters in the house. So a systematic indoor gamma dose measurement has been performed in the dwellings of Agastheeswaram Taluk of Kanyakumari district, which is lying within the 30 km radius from the upcoming Kudankulam nuclear power plant site. The geometric mean of annual absorbed dose from gamma radiation in dwellings has been found to be 278 nGyh(-1). The seasonal variation of indoor gamma dose measurements has also been studied. Significant differences have been observed in dwellings built of different materials such as concrete, tiled, etc.

Population dose from indoor gamma exposure in the dwellings around Kudankulam nuclear power plant

To assess the population dose due to the natural background radiation around the upcoming Kudankulam nuclear power plant, a systematic investigation has been carried out by measuring the indoor gamma dose. In total, 159 dwellings have been selected around the Kudankulam nuclear power plant area i.e. in Radhapuram and Nanguneri taluk (sub-districts) for the measurement. The geometric mean value of indoor gamma dose rate is 305 +/- 48 nGy h(-1) and 273 +/- 50 nGy h(-1) in Radhapuram and Nanguneri taluks (sub-districts), respectively. The annual effective dose due to indoor gamma radiation to the population has been found to be 1.5 mSv and 1.36 mSv in Radhapuram and Nanguneri taluks, respectively.