Gamma Dose Rate Measurements Research Articles

Gamma Dose Rate Measurements in Northern Spain: Influence of Local Meteorological Scenarios on Radiological "False Alarms" in a Real-Time Radiological Monitoring Network.

The present study characterizes gamma dose rate (GDR) concentrations in Bilbao, located in the northern Iberian Peninsula, utilizing a comprehensive 10-min interval database spanning from 2009 to 2018. This station belongs to the radiological environmental monitoring of the Basque Country network. The daily average GDR was found to be 0.07624 ± 0.00004 µSv/h, with the daily 95th percentile averaging 0.08026 ± 0.00007 µSv/h throughout the entire period. Our analysis specifically addresses the impact of precipitation on GDR, revealing a higher correlation coefficient for daily 95th percentile values compared to daily averages. Additionally, the influence of the Galerna (GL) event, a natural meteorological phenomenon in this region, on GDR was investigated, noting that it can develop both with and without precipitation. Understanding the interaction between GDR and this meteorological scenario is vital for the development of more reliable radiological monitoring strategies and for safeguarding public health. For this purpose, 40 GL events were analyzed. The present results indicate that GDR values frequently exceed alarm levels when a GL is formed. These GDR peaks should be considered natural radiological events, necessitating the classification of such GDR peaks as false alarms within the radiological monitoring network. To explain them in detail, 10-min time series of precipitation and radon outdoor concentrations were analyzed. The results demonstrate that the GL event with precipitation is a meteorological scenario that can be associated with false alarms. The present analysis provides a distinct contrast in radon behavior under the same meteorological event in case of being developed with precipitation or without precipitation. The findings from this analysis are crucial for avoiding and understanding false radiological alarms triggered in the monitoring network, thereby enhancing the accuracy of radiological data interpretation and improving public safety measures.

High-performance oxygen terminated synthetic single crystal diamond detector for high gamma dose rate measurement

A high-performance oxygen terminated synthetic single crystal diamond (SCD) detector (4.5 × 4.5 × 0.5 mm3) is presented. The SCD detector exhibits an extremely low leakage current value of 0.29 pA/mm2 with an electric field of 0.3 V/μm. The charge collection spectrum measured with a238Pu source (5.48 MeV α-particles) irradiation shows that the electron and hole charge collection efficiency (CCE) reach as high as 99.1% and 98.9%, with an energy resolution as low as 2.87% and 2.53%, respectively, compared to Si detector. The SCD detector shows excellent radiation hardness and stability under 60Co γ-ray irradiation with a dose rate of 12.737 kGy/h at 150 V bias and is able to withstand a cumulative dose of up to at least 9.3 kGy. The detector output in current mode is linearly related to the dynamic dose rate (0.409 Gy/h-12.737 kGy/h). Similarly, the counting rate of the detector in counting mode exhibits a strong linear variation within the range of 2.6 mGy/h-1269.36 Gy/h. Our results fully indicate that our fabricated SCD detector can be potentially applied to harsh γ irradiation scenarios, which is of guiding significance on real-time dose monitoring.

Ambient Radiological Condition around an Operating Uranium Mill Tailings Disposal Facility at Turamdih, India

AbstractLarge quantity of the feed forms part of the solid waste (tailings) slurry in the low grade uranium ore processing plant at Turamdih in Singhbhum region of Jharkhand, India. Coarser size fraction of this waste is used for backfilling of the underground uranium mines and fine fraction is discharged into an engineered impoundment system or tailings pond. Since inception of the discharges, field expeditions have been performed as part of the comprehensive radiological monitoring program for the facility. The monitoring program broadly consists of ambient gamma dose rate, atmospheric 222Rn and long lived alpha activity measurement around the facility and the estimation of radionuclide in diverse environmental matrices collected from the adjoining sites. Findings reflect that the radiological conditions are comparable to the pre-existing background level adjoining the tailings pond impoundment. Further, measurements for more than a decade confirm that the atmospheric radon concentration profile just a few meters beyond the embankment is indistinguishable from the background.

A large and feasible national survey representative of population exposure to outdoor gamma radiation in urban areas.

Although data on outdoor gamma radiation are available for many countries, they have generally been obtained with measurements performed in undisturbed environments instead of in urban areas where most of the population lives. Only one large national survey, with on-site measurements in urban areas, has been identified worldwide, probably due to high costs (e.g., personnel and instrumentation) and difficulties in selecting measuring points. A campaign of outdoor gamma radiation measurements has been carried out in the entire Italian territory. All measurement points were selected at the infrastructures of an Italian telecommunications company as representatives of all the possible situations of outdoor exposure to gamma radiation for population in urban areas. Ten replicates of portable gamma (X) detectors carried out all the measurements. Approximately 4,000 measurements have been performed. They are distributed across 2,901 Italian municipalities, accounting for 75% of the Italian population. The national population-weighted mean of the gamma ambient dose equivalent rate (ADER) is 117 nSv h-1, and it ranges from 62 to 208 nSv h-1 and from 40 to 227 nSv h-1 for 21 regions and 107 provinces, respectively. The average variability at the municipal level, in terms of the coefficient of variation (CV) is 21%, ranging from 3 to 84%. The impact of land coverage and the distance from a building on the outdoor gamma radiation level was assessed with complementary measurements, leading to differences ranging from -40 to 50% and to 50%, respectively. A representative campaign of outdoor gamma dose rate measurements has been performed in Italy, only in urban areas, to assess the exposure effect due to outdoor gamma radiation on the population. It is the largest national campaign in urban areas worldwide, with a total of 3,876 on-site measurements. The land coverage and the distance from surrounding buildings were recognized to strongly affect outdoor gamma radiation levels, leading to high variability within small areas. The collaboration with a company that owns a network of facilities on a national territory as dense as the residing population made this survey feasible and affordable. Other countries might adopt this methodology to conduct national surveys in urban environments.

Source term inversion of nuclear accidents based on ISAO-SAELM model

The release source term of radioactivity becomes a critical foundation for emergency response and accident consequence assessment after a nuclear accident Rapidly and accurately inverting the source term remains an urgent scientific challenge. Today source term inversion based on meteorological data and gamma dose rate measurements is a common method. But gamma dose rate actually includes all nuclides information, and the composition of radioactive nuclides is generally uncertain. This paper introduces a novel nuclear accident source term inversion model, which is Improve Snow Ablation Optimizer-Sensitivity Analysis Pruning Extreme Learning Machine (ISAO-SAELM) model. The model inverts the release rates of 11 radioactive nuclides (I-131, Xe-133, Cs-137, Kr-88, Sr-91, Te-132, Mo-99, Ba-140, La-140, Ce-144, Sb-129). It does not require the use of the physical field of the reactor to obtain prior information and establish a dispersion model. And the robustness is validated through noise analysis test. The mean absolute errors of the release rates of 11 nuclides are 15.52 %, 15.28 %, 15.70 %, 14.99 %, 14.85 %, 15.61 %, 15.96 %, 15.42 %, 15.84 %, 15.13 %, 17.72 %, which show the significant superiority of ISAO-SAELM. ISAO-SAELM model not only achieves notable advancements in accuracy but also receives validation in terms of practicality and feasibility.

Побудова картосхем щільності забруднення 137Cs сільськогосподарських угідь за сукупністю результатів обстеження

A methodology for mapping the density of 137Cs contamination of agricultural land is proposed and tested. The methodology is based on data on gamma-dose rate measurements, gamma-logging results, and direct determination of 137Cs in soil samples, which were obtained by different organizations in different years. It allows to generalize all available information on 137Cs contamination of the lands and significantly improves the representativeness of estimates of the spatial distribution of the radionuclides at the mapping.

Novel epoxy-bPBD-BisMSB composite plastic scintillator for alpha, beta and gamma radiation detection

A composite plastic scintillator is prepared by uniform dispersion of organic fluorophores 2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (b-PBD) and 1,4-bis(2-methylstyryl) benzene (Bis-MSB) in epoxy resin followed by curing at room temperature. The developed scintillator is strong blue emitter (425 nm), confirmed by 365 nm UV excited Photo luminescence and beta particle (90Sr-90Y) excited Radio-luminescence characterizations. The developed scintillator is highly transparent (~ 70%) to emitted light wavelength. Moreover, the scintillator’s blue emission is appropriate for photomultiplier tube (PMT) based scintillation measurement due to its maximum peak spectral response in blue region. Alpha, beta and gamma radiation detection were performed on PMT coupled scintillators of sizes Ø50 mm × 1 mm, Ø50 mm × 5 mm and Ø50 mm × 25 mm respectively. Pulse height spectra were recorded using 1 k Multichannel analyser (MCA) using various reference radiation sources. All scintillators demonstrated promising response to the respective radiations. Absolute detection efficiency of alpha scintillator is obtained as 32% (241Am), 86% of that of standard plastic scintillator EJ-212. Beta endpoint energy and gamma Compton edges showed linear variation w.r.t. corresponding channel numbers. Detection efficiency of beta and gamma scintillator is found to be 35.7% (90Sr-90Y) and 6.7% (136Cs) respectively. The developed scintillator has potential to be used for radioactivity contamination & gamma dose rate measurement applications.

To what extent do field conditions affect gamma dose rate determination using portable gamma spectrometry?

Field gamma spectrometry is a widely used approach for determining in situ gamma dose rates in dosimetric (i.e., electron spin resonance and luminescence) dating applications. In comparison with laboratory-based determinations, in situ radioactivity measurements typically provide more representative gamma dose rate evaluations for heterogeneous sedimentary environments. However, it is often not possible to perform in situ gamma spectrometry measurements under carefully controlled conditions that are directly comparable to those originally used for equipment calibration.In this study, we use Geant4 Monte Carlo simulations to model gamma spectrometry measurements under a range of field conditions, and examine the relative impacts of the following parameters on dose rate determination using the threshold calibration approach: (i) geometry and depth of the measurement hole in which the probe is inserted, (ii) nature of the sediment or rock materials and their water content, (iii) geometry of the radiation environment surrounding the measurement hole, i.e. closed and partially closed sites (e.g., caves, trenches) versus open-air sites (e.g. plain field excavations, cliff or cutting exposures).Our results show that some differences in calibration and field measurement configurations can significantly bias in situ gamma dose rate determinations. Variations in the depth of probe holes can result in underestimations of infinite matrix gamma dose rates by 5% for a 30 cm-deep hole to 58% for measurements made against sediment surfaces (i.e., 2π geometry). Use of hole shapes that do not match those of the probe can lead to underestimations of infinite matrix dose rates by up to 4%, with these biasing effects becoming more significant for shallow holes. External gamma radiation originating from, and backscattered against, structures in the surrounding environment can contribute significantly to gamma dose rates measured using shallow probe holes. The nature of the mineral materials can have a small effect on the measured gamma dose rate (equivalent to infinite matrix dose rate biases of a few percent), mostly due to differences in the density of different materials. Measurements performed in materials with high water contents can be affected by small gamma dose rate overestimations due to differences between water attenuation factors of centimetre-scale objects such as gamma spectrometer probes and those of relevance for dating smaller objects such as sediment grains. These problems can be resolved by using specific correction factors, by including additional uncertainties during dose rate determination, or by performing in situ measurements at different depths for the same location.

Measurement of radon mass exhalation and gamma dose rates in the Chakrata region of Garhwal Himalaya, India

Measurement of radon mass exhalation and gamma dose rates in the Chakrata region of Garhwal Himalaya, India

Direct gamma dose rate measurement and assessment of excess lifetime cancer risk.

In this study, in some neighborhoods in Kahramanmaraş province of Turkey, indoors and outdoors direct gamma dose rate measurements have been done. All of the gamma dose rate measurements have been made at ground level and at the height of 1m from the ground. The median values of the gamma dose rates on the ground and 1m above the ground indoors are 70.34±7.74 and 49.53±5.39nGy h-1, respectively. Outdoor measurements have been carried out on both soil and asphalt floors. The average values of gamma dose rate on the ground and at a height of 1m outdoors (soil floor) are 68.16±7.49 and 53.50±5.88nGy h-1, respectively. The mean values of gamma dose rate on the ground and 1m above the ground outdoors (asphalt floor) are 61.63±6.77 and 48.69±5.35nGy h-1, respectively. Indoor and outdoor average gamma dose rates are below the mean world. In addition, using the measured gamma dose rate values, annual effective dose equivalent (AEDE) and excess lifetime cancer risk (ELCR) for adults have been calculated. The total AEDE and ELCR (on soil floors and indoors at 1m above ground level) are 0.31±0.03mSv y-1 and 1.08±0.10×10-3, respectively. The total AEDE and ELCR (on asphalt floors and indoors at 1m above ground level) are 0.30±0.03mSv y-1 and 1.06±0.10×10-3, respectively. The AEDE and ELCR for adults living in the neighborhoods within the scope of the study in Kahramanmaraş city center within 1y are lower than the average world.

Measurements of Terrestrial Gamma Dose Rate Distributions along Idiroko Road, Ota, Ogun State, Nigeria: Health Implications on Roadside Dwellers

An extensive study concerning the terrestrial gamma dose rates of the surface soils from Canaanland entrance Road, Ota to Eleha Complex along Idiroko Road, Ota has been carried out to cover the road running across both areas. The In-situ measurements of gamma dose rates and radionuclides were carried out using the Gamma detector (Super Spec RS 125). The result shows that the average outdoor gamma dose rate in the study area is 73.57 nGyh−1. The average values of the radionuclides obtained were 32.9 Bq/kg for 238U, 68.4 Bq/kg for 232Th, and 328.7 Bq/kg for 40K. The background dose rate of 113.3 nGy/h was found in station 9 and is twice higher than the recommended permissible limit of 59 nGy/h suggested by UNCSEAR, 2000, and ICRP, 1999, respectively. Results were obtained based on radiological parameters for the outdoor absorbed dose rate (Dout) with a mean value of 73.57 nGyh−1, the indoor absorbed dose rate (Din) with a mean value of 131.84 nGyh−1, the annual effective dose rate (AEDR) with a mean value of 0.74, the radium equivalent (Raeq) with a mean value of 156.0, the internal hazard index (Hin) with a mean value of 0.51, the external hazard index (Hex) with a mean value of 0.42 and the excess lifetime cancer risk (ELCR) with a mean value of 2.57. Similarly, results obtained from estimated radiological parameters show that the station with the highest value for radium equivalent (Raeq), external hazard index (Hex), internal hazard index (Hin), and annual effective dose rate (AEDR) is Station 9 at 237.91 Bq/Kg, 0.64, 0.72 and 1.13 mSvy−1 respectively while the station with the lowest value for radium equivalent (Raeq), external hazard index (Hex), internal hazard index (Hin) and annual effective dose rate (AEDR) is Station 17 at 85.58 Bq/Kg, 0.23, 0.27 and 0.40 mSvy−1 respectively. This study will serve as a guide on assessing the road construction materials on radioactive contents before application to reduce the exposure risks to the populace along the busy roadsides.

Identification and quantification of anomalies in environmental gamma dose rate time series using artificial intelligence

Gamma dose rate (GDR) monitors are the most widely used tool for continuous monitoring of environmental radioactivity. They are inexpensive to procure and operate, and generally require little maintenance. However, since no spectral information is available, the detection limit for irregularities is correspondingly high; A value around 20 nSv/h is often called out.By adding weather data to the GDR measurement and a sequence of machine learning algorithms, the anomaly detection sensitivity can be significantly increased while simultaneously decreasing the number of false positives. The algorithms were designed such that an integrated safety net prevents false negatives. First, the precipitation-induced GDR peaks from washed-out Radon progeny are removed by means of regression, provided that a check of the regression parameters shows sufficient agreement with past data at the measurement site. A neural network then calculates the expected value of the remaining GDR baseline for the prevailing conditions. Finally, an anomaly detection is carried out on the remainder between the expected and actual GDR baseline value. Extreme value theory is used to detect point anomalies, and hierarchical clustering of subsequences for slower processes. By combining the two detection methods, the full spectrum of irregularities is covered.The algorithms were implemented in Python and trained with real measurement data from the German GDR monitoring network. For verification, the data were enriched with results from JRODOS simulations of a nuclear power plant accident. Altogether, the presented methodology can lower the detection limit of irregularities to about 4 nSv/h, i. e. about a factor of 5 below the previous consensus value. The algorithm detects as well as quantifies the anomaly in the GDR, allowing for additional conclusions like potentially involved isotopes. Most important, it allows to refrain from the current practice of defining fixed alarming thresholds between the two contradicting goals of high sensitivity and low false alarm rate. Instead, it allows to transition to the more natural alarming on deviations from the expectation.

Identification of high radon dwellings, risk of exposure, and geogenic potential in the mining area of the "TREPČA" complex.

This study was performed to investigate radon levels in dwellings in the mining area near the town of Kosovska Mitrovica. The Passive radon technique based on the charcoal canister test kit conducted in summer and autumn 2019 showed unexpected results. The reference level of 300 Bq/m3 for indoor radon concentration was exceeded in 15 of 26 dwellings. Preliminary measurements of gamma dose rate in some dwellings built from local stone showed values from 0.30 to 0.45 μSv/h, while 75% of measurements in dwellings with stone foundations had radon above the reference level. The highest radon concentration (22 500 ± 220Bq/m3 ) was measured in the cellar of one family house. The RAD7 device (Durridge Company, Inc.) was used to measure radon concentrations in water and nearby soil of some dwellings. Indoor radon concentration fluctuated significantly over two days; over a one-day time scale, radon varied from 2843 ± 217 Bq/m3 at midnight to 1449 ± 104 Bq/m3 in the morning at one site, and abruptly decreased from a maximum of 2146 ± 262 Bq/m3 in one day to a minimum of 21 Bq/m3 the next day at another site. The influence of geological substrate on radon exposure was discussed through the estimation of geogenic radon potential, which varies from low the high radon index despite to high permeability of soil.

Harmonization and mapping of terrestrial gamma dose rate data in Belgium

With several databases available, including two sets of in situ measurements of the ambient gamma dose rate and an airborne survey of K, Th, U in soil, Belgium is a favourable case for exploring the mapping methodology for terrestrial radiation.The first step is the harmonization of the different data sets, taking in situ measurements with an ion chamber as the reference. Corrections are necessary, based on the data themselves (a) to the measurements of permanent monitoring stations, (b) to the data calculated from airborne measurements of the soil activity, due in particular to the attenuation by the forest cover, and (c) to the other data calculated from the soil activity, due to the lower activity of the upper layer. After subtracting the cosmic contribution, a harmonized database of the terrestrial gamma dose rate (TGDR) based on 379 in situ measurements was built, together with a harmonized data set of 30134 TGDR values calculated from the concentrations of K, Th, U in soil deduced from the airborne survey. The two data sets are in good agreement with each other for all statistical characteristics that were examined like basic statistics, qq-plots, analysis of variance (ANOVA) or variograms, which validates the airborne-based data set by the link with in situ ion chamber measurements.ANOVA reveals the strong relation between TGDR and the soil class, which justifies the use of a soil map as the framework for developing the TGDR map. The variograms show the absence of residual spatial correlations within soil classes. The two harmonized TGDR data sets were mapped at the nodes of a kilometric grid by the moving average method within soil groups. There is a rather good agreement between the maps, confirming the equivalence between the two data sets and the validation of the airborne based one, which can obviously give more detail.After reducing the maps to a 10 km × 10 km grid, the two data sets were used to check the accuracy of the Belgian part of the European TGDR contained in the European Atlas of Natural Radiation.

Walking survey technique for ambient gamma dose rate measurement established in Fukushima Medical University

ABSTRACT This study aimed to establish a walking survey technique for rapidly determining the distribution of the ambient gamma dose rate. The measurement system consists of a scintillation spectrometer and a Global Positioning System receiver, which are controlled using a laptop. In addition to locality information, the ambient gamma dose rates were measured continuously and corrected based on shielding by the measurer body. The measurement interval was optimized at 12 s based on the locality resolution and fluctuations of the measured dose rates. A comparison was also made between the dose rate distribution maps depicted by the walking survey technique and spot measurements at fixed points. Based on the measurement data selected for the comparison, it was found that the values of 80% of the data obtained using the walking survey technique deviated within ±20% relative to those obtained by spot measurements. Compared to the spot measurements, the time taken to depict the map was reduced to one-fifth, and the localized contamination points could be depicted.

Silicon substrate diamond film detector for gamma dose rate measurement in a high radiation environment

A detector that can accurately measure gamma (γ) rays in a high radiation environment was developed to detect high-intensity and high-energy γ rays in deep space. Traditional semiconductor detectors cannot work in high radiation environments for a long time, and pure single-crystal diamond detectors cannot be popularised on a large scale due to their high cost. We proposed a diamond γ-radiation (SD) detector with a highly oriented diamond film structure on a highly oriented boron-doped silicon substrate to measure γ-dose rate in high radiation environments. The SD detector was developed using several microelectromechanical processes, such as microwave plasma chemical vapour deposition. Consequently, in radiation from the 12,000 Ci 60Co source, when the dose rate was 200 Gy/h, the output signal could stabilise within 1 s. Within the dose rate of 10–190 Gy/h, the output showed a linear relation with the changing dose rate. The detector sensitivity reference value was S = 2.08 × 10−20 C · cm2 at a distance of 3.61 m from the 12,000 Ci 60Co source. Our study can provide guidance for deep space γ-ray detection.

Management of nuclear materials containing natural uranium and thorium salts

This paper highlights an experimental model proposed for the management of nuclear materials containing natural uranium and thorium salts, based on technical and legislative methods. The investigated nuclear materials originate from laboratory chemicals with expired validity, having as manufacturers companies specialized in the manufacture of laboratory substances such as: Merck, Chemapol, Sigma Aldrich, Bucharest Reagent. The experimental program refers to several issues of great importance in the waste and environmental management, such as: a) the processing of radioactive substances containing nuclear materials and radioactive waste represented by solid objects contaminated with radionuclides from the radioactive series of U-238 and Th-232; b) gamma dose rate measurement during handling and processing of open sources of ionized radiation; c) measurement of suspicious contamination of the operating personnel which handles the equipment, including the materials used in the processing of open sources of ionizing radiation; and d) the inventory of nuclear materials according to the chemical formula, the mass of chemical substance, the mass of the nuclear element in each container and type of packaging. For the good development of processing these open sources of ionizing radiation containing nuclear materials, the ALARA principle (As Low As Reasonably Achievable) was applied, which is fundamental to the principles of radiation protection. All the measurements for determining the gamma dose rate and suspicious contamination were performed with the aid of a CoMo 170 radiometric device produced by Nuvia Instruments Gmbh Germany, equipped with a 170x100 mm2 PL detector with zinc sulfide calibrated with the aid of C-14, Co-60, Cs-137, U-238 and Am-241 radioactive isotopes and an external probe containing a scintillating crystal with sodium iodide enriched with thallium calibrated with Cs-137.

Indoor radon, external dose rate and assessment of lung cancer risk in dwellings: the case of Ebolowa town, Southern Cameroon

ABSTRACT The present work reports indoor Radon-222 activity concentration measurements, external gamma dose rate measurements, and assessment of cancer risk in the different dwellings in Ebolowa town, southern Cameroon. The geological formations of this studied area are mainly granites. This studied area extends over the equatorial climatic zone. The mean temperature of the zone varies from 25°C to 26°C with two rainy and two dry seasons with a relative humidity of (70–80) % recorded throughout the year. The indoor radon activity concentrations were carried out using RADTRACK2 devices, which are the alpha track detectors made of CR-39 plastic films contained in an antistatic black holder. Each device was hung in an inhabited room of each selected dwelling for an average period of three months. Radon concentrations in dwellings ranged between (23 ± 10) Bq m–3 and (2620 ± 480) Bq m–3 with an arithmetic mean of 135.6 Bq m–3 and a geometric mean of 63 Bq m–3. The estimated annual effective doses due to external gamma exposure ranged from (0.15 ± 0.01) mSv y−1 to (0.38 ± 0.06) mSv y−1 with an average value of 0.26 mSv y−1. The estimated annual effective dose due to indoor radon ranged between 0.43 mSv y−1 and 49.6 mSv y−1 with an arithmetic mean of 2.6 mSv y−1. This value was below the International Commission on Radiological Protection (ICRP) recommended action level. The Excess Lifetime Cancer Risk (ELCR) ranged from 1.39% to 158% with a mean value of 8.2%. According to these results, cancer risk due to inhalation of radon-222 must be further investigated in the population living in Ebolowa town.

Factorial kriging for estimating and mapping the geochemical background from in situ gamma dose rate measurements downstream of a former uranium mine

A geostatistical approach is applied for extracting the geochemical background from gamma dose rate data acquired downstream of a former French uranium mining area. The exploratory data analysis shows that the spatial structure of the gamma dose rate consists of two components: a short isotropic component (10 m-range) that corresponds to the geochemical background; and a long anisotropic component (30–60 m-range) that corresponds to the drainage network features previously fed by the mine discharge water. The gamma dose rate on the whole area of interest was estimated and simulated (to deal with uncertainties) through a kriging of the measured values. The spatial component related to the geochemical background was then extracted through factorial kriging. The proportion of the gamma dose rate explained by the geochemical background according to factorial kriging is consistent within uncertainties with geochemical analyses performed on soil and sediment samples. This study thus highlights the potential of such geostatistical approaches for better exploiting radiometric data.

Validation of a modified FLEXPART model for short-range radiological dispersion and dose assessments in ONERS Decision Support System

Online Nuclear Emergency Response System (ONERS) is a GIS based Decision Support System developed for the management of Off-Site Nuclear Emergencies at Nuclear Power Plant (NPP) sites in India. As part of this development, the FLEXPART model is modified to compute atmospheric dispersion using observations from the local meteorological tower for the estimation of concentration and radiological dose over short-range range in realtime. In this work, the modified FLEXPART is validated for dose assessments using gamma dose rate measurements by Autonomous Gamma Dose Loggers installed around the Pressurized Heavy Water Reactor (PHWR) of Madras Atomic Power Station (MAPS) at Kalpakkam site in southeast India. The plume exposure dose is computed in two pathways i) cloudshine dose by incorporating a point kernel algorithm ii) submersion dose by semi-infinite plume method using FLEXPART. Comparison of model estimates with detector data for the 8-day period (01–08 December 2017) covering various atmospheric conditions indicates that the simulated cloud gamma dose rate is in good agreement with observed dose under stable, neutral, and unstable conditions with a coefficient of determination of 0.66, 0.73 and 0.49 respectively. The overestimation of dose under unstable conditions could be due to underestimation of mixed layer height (h) and convective velocity scale (w*) computed using the local similarity approach while using tower data, which needs further insights for improvements.