Distribution Of Radionuclides Research Articles

Natural Radioactivity and Dose Assessment of Sediment Samples of Kerala Coast, India

Gamma spectrometry was employed to determine activity concentration of naturally occurring radionuclides 238U, 232Th and 40K in sediment samples collected from Vellanathuruthu to Thumpoly of Kerala Coast using NaI(Tl) detector and to evaluate the radiation hazards. The levels and distribution of radionuclides in sediments from this coastal area have been determined. The activities ranges and mean (in bracket) values for 238U, 232Th, and 40K are 78.92 to 1493 Bq kg−1 (552.63), 94.76 to 2856.46 (851.24) Bq kg−1 and 30 to 2399.20 (678.61) Bq kg−1 respectively. The mean activity of 238U, 232Th, and 40K are higher than the global average values (35 Bq kg−1 for 238U, 400 Bq kg−1 for 40K, and 30 Bq kg−1 for 232Th) of these radionuclides in the sediment and it may be due the presence of rich deposits of black sands. The radium equivalent activity was estimated to range from 216.74 to 5762.48 Bq kg−1 (1822.17). The average absorbed dose rate was determined to vary from 94.96 to 2515.83 nGyh−1 (797.97) and the annual effective dose was estimated to range from 0.12 to 3.09 mSvy−1 (0.98). Additionally, it was estimated that the average external hazard index was 4.92 and the average internal hazard index was 6.41 respectively. The computed radiation indices for all samples were compared to internationally accepted standards, showing that they are above the recommended limits. The results of the present investigation indicate that the radioactivity in the region is slightly above the global average values.

Calculation and application research on real-time source term diffusion in NPP auxiliary building under accident circumstances

Abstract In the light of radioactive material leakage (due to containment bypass or failure) to the auxiliary building and its service compartments under severe accident circumstances, key techniques related to accident source terms in the nuclear emergency building were researched. During the research, the source-term diffusion and migration patterns were simulated in the building compartments, including the simulation of the gradual diffusion and decay process (driven by circulating air) of fission-derived gases and aerosol toward each compartment. Besides that, by taking a M310 unit at Fangjiashan NPP as the application object, the scenarios of initial accidents of LB/MB/SB-LOCA, MSLB and SGTR were chosen to establish a real-time diffusion calculation model for in-building radioactive source terms under nuclear accident circumstances. While considering the circumstances before and after being intervened by accident mitigation measures, the concentration distribution of radionuclides in the auxiliary building and personnel total-exposure radiation dose rate were quickly assessed online, and a basis was provided for the visualization of radiation dosage and the assessment of received radiation dosage and injury & death hazards during personnel activities outside the main control room.

A new tool for estimation of the in vivo distribution of intake radionuclides.

This study developed a more universal tool for estimating the in vivo distribution of intake radionuclides. The biokinetic models and transfer rates for intake radionuclides were cited from the publications of the International Commission on Radiological Protection (ICRP), and the models were transformed into a series of linear differential equations and numerically solved using the Scipy algorithm in Python. The user interfaces for model selection, data input and in vivo distribution calculations were designed using PyQt5. The calculation results of the new tool are completely consistent with those of the data viewer released by the ICRP and are also very similar to other reported values. The new tool allows users to select and change the biokinetic models and transfer rates and display the in vivo distribution of radionuclides in an image format. It is much more user friendly.

Radionuclides distribution in soils and radon level assessment in dwellings of Mungo and Nkam Divisions, Cameroon.

Radionuclide and radon levels have been investigated in soil samples and residential environments within the Mungo and Nkam Divisions of the Littoral Region. These analyses employed gamma spectrometry facilitated by a NaI (Tl) detector for soil samples, yielding average activity concentrations of 226Ra, 232Th, and 40K at 23.8, 72, and 105Bqkg-1, respectively. Various radiological parameters were calculated to evaluate radiological hazards. Additionally, the indoor radon concentrations were quantified utilizing the CR-39 solid-state nuclear track detector (Radtrack), revealing an average concentration of 25Bqm-3 and an associated inhalation dose of 0.66mSv y-1. Risk assessments for lung cancer attributable to indoor radon exposure incorporated models such as the Harley model. An observed moderate correlation between indoor radon levels and external 226Ra concentrations implies that radon intrusion indoors might be substantially influenced by the 226Ra present in the subjacent soil, considering the construction of residential structures directly upon these terrains.

Distribution of radionuclides in the soils and assessment of radiation hazards in AL Najaf, Iraq: A cross sectional analysis.

To evaluate radioactivity levels in soil samples and their physical impact on the population. The experimental radiation study was conducted by researchers belonging to the Kufa University in Al- Najaf, Iraq, in August 2020, and comprised soil samples from Al-Rahma area. Sodium iodide detector activated with a trace amount of Thallium with crystal dimensions 3" x 3" was used to calculate the concentration of Radium, Thorium and Potassium. Among the 15 samples collected, the average ± standard deviation (SD) concentration for Radium, Thorium and Potassium was 0.1776±0.12, 0.726±0.435 and 1.9128±1.105%, respectively. The reported value of excess lifetime cancer risk was 1.2819×10-3. The area studied was found to be a safe area and did not pose a health threat to the locals.

Transplanted Murine Tumours SPECT Imaging with 99mTc Delivered with an Artificial Recombinant Protein.

99mTc is a well-known radionuclide that is widely used and readily available for SPECT/CT (Single-Photon Emission Computed Tomography) diagnosis. However, commercial isotope carriers are not specific enough to tumours, rapidly clear from the bloodstream, and are not safe. To overcome these limitations, we suggest immunologically compatible recombinant proteins containing a combination of metal binding sites as 99mTc chelators and several different tumour-specific ligands for early detection of tumours. E1b protein containing metal-binding centres and tumour-specific ligands targeting integrin αvβ3 and nucleolin, as well as a short Cys-rich sequence, was artificially constructed. It was produced in E. coli, purified by metal-chelate chromatography, and used to obtain a complex with 99mTc. This was administered intravenously to healthy Balb/C mice at an activity dose of about 80 MBq per mouse, and the biodistribution was studied by SPECT/CT for 24 h. Free sodium 99mTc-pertechnetate at the same dose was used as a reference. The selectivity of 99mTc-E1b and the kinetics of isotope retention in tumours were then investigated in experiments in C57Bl/6 and Balb/C mice with subcutaneously transplanted lung carcinoma (LLC) or mammary adenocarcinoma (Ca755, EMT6, or 4T1). The radionuclide distribution ratio in tumour and adjacent normal tissue (T/N) steadily increased over 24 h, reaching 15.7 ± 4.2 for EMT6, 16.5 ± 3.8 for Ca755, 6.7 ± 4.2 for LLC, and 7.5 ± 3.1 for 4T1.

Bioaccumulation of natural radionuclides in edible molluscs and associated risk from the Ashtamudi Estuary, situated in a high background natural radiation zone (HBNRA), Kerala, southwest coast of India

The study investigated various natural radionuclides, including 238U, 232Th, 210Po, and 210Pb, in edible molluscan species collected from different zones of the Ashtamudi estuary. Physicochemical and sedimentological factors played crucial roles in influencing the distribution of radionuclides in water and sediments. Notably, bivalve species, particularly those from the Cyrenidae family, exhibited significant bioaccumulation of 210Po (up to 432.8 Bq kg−1) and 210Pb (up to 121.3 Bq kg−1), with Zone VI recording the highest biological concentration factor (BCF) and biological sediment accumulation factor (BSAF). The calculated effective dose for humans consuming bivalve meat was moderate, falling above the lower end of the ICRP range of 1 mSv y−1 but well below the upper limit of 20 mSv y−1 for existing elevated radiation zones. The intake of radioactivity from some bivalves corresponded to a cancer risk of approximately 3.2 × 10−2 (total mortality + morbidity), exceeding the acceptable risk threshold reported by the USEPA. However, this level of exposure indicated that immediate action might not be necessary, especially if further dose reduction proved impractical, in line with the ICRP's approach to optimizing radiation protection.

Dosimetry at cellular level for the alpha-emitting radionuclides actinium-225, astatine-211 and radium-223 for bone metastasis cells from castration resistant prostate cancer.

Objectives.The aim of this work is to evaluate energy deposition in the nucleus and cytoplasm in targeted alpha therapy of metastatic castration-resistant prostate cancer by modeling two cell lines, PC3 (osteolytic) and LNCaP C4-2 (osteoblastic), for actinium-225, astatine-211, and radium-223 and their progeny, using Monte Carlo simulations with the GATE/Geant4 code.Approach.We developed single cell and cell clusters models to Monte Carlo simulations, performed on the GATE platform version 9.3, with the GEANT4-DNA physics list emstandard_opt3_mixed_dna for At-211, Ac-225 and Ra-223 progenies. We considered three radionuclide distributions as a sources: the nucleus, the cytoplasm and the whole cell.Main results.When the nucleus was considered as a target, theS-values (N←N) calculated for At-211, Ac-225 and Ra-223 progenies were significantly higher, within 60%-90%, thanS-values (N←Cy), demonstrating less influence of cytoplasm only internalization. When the cytoplasm was considering as a target, theS-values (Cy←Cy) calculated for At-211, Ac-225 and Ra-223 progeny were significantly higher, within 30%-90%, than theS-values (Cy←N). When no progeny migration occurs and for target nucleus , the cumulativeS-values (N←N) calculated for At-211, Ac-225 and Ra-223 were significantly higher, within 50%-70%, than theS-values (N←N) computed for At-211, Ac-225, and Ra-223. Comparing the cumulativeS-values, Ac-225 and Ra-223 therapies is more effective, in terms of deposited energy in a target, than that with At-211.Significance.The data presented in this research indicates that Ac-225 therapy may be the optimum choice due to the energy deposited in the nucleus, as long as the recoil effects and redistribution of progeny are understood. In contrast, At-211 is an alternative to avoid progeny migration. However, to completely analyze the efficacy of radionuclide therapy, other parameters must be considered, such as biological half-life, stability of the transport molecule, progeny migration, excretion pathways, and uptake in different organs.

Content and Distribution of Radionuclides in the Profile of Light Gray Forest Soil and Agrocenosis Plants

The results of long-term radiation monitoring of light gray forest soil and cultivated plants of the reference area are presented. Correlation analysis has determined the relationship between the distribution of artificial and natural radionuclides in the soil profile with its agrochemical properties. The distribution of radionuclides in the soil profile is determined by the intensity of the podzolic process. The profile shows the eluvial-illuvial differentiation of radionuclides, when an increase in their accumulation occurred in the illuvial horizon. According to the density of contamination of the surface soil layer with cesium-137 and strontium-90, a satisfactory level of the environmental situation was determined, according to which the soil of the site is classified as uncontaminated. Rows of cultivated plants with an increasing ability to accumulate caesium-137 and strontium-90 from the soil have been constructed. The grain of all grain crops accumulated less cesium-137 and strontium-90 compared to straw. All grown plant products of all types of crops fully met veterinary and hygienic standards for the content of caesium-137 and strontium-90 in feed (green mass, straw and feed grain) and food grains. The coefficients of accumulation and transfer of caesium-137 and strontium-90 from soil to plants were calculated.

Simultaneous recycling of both desalination reject brine water and phosphogypsum waste in manufacturing K2Mg(SO4)2·6H2O fertilizer

The purpose of this paper is twofold. The first is to convert phosphogypsum (PG) waste, mainly composed by gypsum (CaSO4·2H2O), into potassium sulfate (K2SO4) compound, which help to reduce the environmental impact and open new ways and valuable chain for the industrial manufacturing of phosphoric acid. The second is to recover MgSO4·7H2O from desalination reject brine water (RBW), thereby minimizing its associated environmental impact. The novelty of the current study is to simultaneously use the recovered salts K2SO4 and MgSO4·7H2O to produce K2Mg(SO4)2.6H2O (K2MgS6), considered as a double fertilizer. Additionally, Solid–Liquid Equilibria (SLE) are frequently applied to several industry domains. SLE are an interesting outline to visualize the precipitation, separation, and purification of a solid phase and the pathways by which crystallization can occur. The SLE of the ternary phase diagrams K2SO4-MgSO4-H2O at 25 °C and 0 °C were especially used to successfully determine the operating conditions and the design of a crystallization process during the PG/RBW conversion into K2MgS6. Several characterization techniques (i.e., XRD, DTA/DTG, SEM/EDS, FTIR) were employed to identify the solids formed during this process. An analysis on the distribution of natural radionuclides and heavy metals was carried out to confirm the effectiveness of the developed process. The main conclusion of this study was that K2MgS6 fertilizer can be manufactured by combining PG and RBW from desalination plants. Furthermore, the formed fertilizer, K2MgS6, is highly recommended for many applications in the agriculture sector.

Natural radionuclide profiles and radiological risks in soils and rocks of the Koytash-Ugam Range, Uzbekistan.

This investigation quantifies the activity concentrations of natural radionuclides (226Ra, 232Th, and 40K) in the soils and certain rocks of the Koytash-Ugam Range, Uzbekistan, and assesses their radiological risks. Gamma-spectrometric analysis of soil and rock samples revealed activity concentrations ranging from 456.2 ± 56.0 to 813.9 ± 76.0Bqkg-1 for 40K, 18.2 ± 6.3 to 70.0 ± 12.0Bqkg-1 for 226Ra, and 30.1 ± 2.9 to 57.9 ± 10Bqkg-1 for 232Th. This data indicates a heterogeneous distribution of radionuclides, informing radiation safety and health risk assessments on a global scale. The calculation of radiological hazard indices, including the alpha-index (ranging from 0.09 to 0.35), gamma-index (ranging from 0.40 to 0.73), and both internal (ranging from 0.40 to 0.54) and external (ranging from 0.36 to 0.54) hazard indices, was undertaken to ascertain potential health risks. The radium equivalent activity ranged from 108.4 to 199.3Bqkg-1, and the absorbed dose rates were 51.0-93.3 nGy h-1 indoors and 96.6-178.2 nGy h-1 outdoors. These metrics underlie the estimated annual effective dose of 536.5-988.5 × 10-3mSv y-1, highlighting the variability in radiation exposure. Additionally, the potential lifetime cancer risk was projected at 1770.4 to 3262.0 per million, with an annual gonadal dose equivalent of 361.9 to 655.5 μSv y-1, reflecting natural background radiation influence. The results underscore the importance of safe material use in construction and the necessity for routine natural radioactivity monitoring. Radon flux density (RFD) values within acceptable construction limits (26-176mBqm-2s-1) suggest the area's suitability for development, considering recommended safety guidelines. This study not only aids local environmental and public health frameworks but also enriches the international knowledge base, facilitating comparative studies for the advancement of global radiation protection standards. Through a detailed examination of radionuclide distribution in an under-researched area, our research highlights the critical need for integrated international approaches to natural radiological hazard assessment.

Radiological Analyses of 226Ra and 238U in Surface Water and Sediments from the Jackpile Member of the Morrison Formation, Pueblo of Laguna, New Mexico.

Surface water and sediments from the Jackpile mine, St. Anthony mine, Rio Paguate, Rio Moquino, and Mesita Dam areas near Pueblo of Laguna, New Mexico, were analyzed for 226Ra and U using gamma (γ) spectroscopy and inductively coupled plasma mass spectroscopy, respectively. Activity ratios for 226Ra/238U for solid samples range from 0.34 ± 0.13 to 16 ± 2.9, which reflect uranium transport and accumulation (<1), relatively pristine material in secular equilibrium (1), and removal of uranium by weathering (>1). Concentrations ranging from 80 to 225 μg L-1 U were detected in unfiltered water samples near the Jackpile mine. Water samples upstream and downstream from the mine contained concentrations ranging from 12 to 15 μg L-1 U. Water samples collected from the North Pit standing pond in the Jackpile mine contained as much as 1560 pCi L-1 of 226Ra, and passing the water through a 0.2 μM filter did not substantially reduce the activity of 226Ra in the water. 234Th and 226Ra are in secular equilibrium in this water, while radon gas was lost from the water. The results of the current study provide insight into the distribution of U-series radionuclides in the Pueblo of Laguna area, including detection of high levels of radioactivity in water at some locations within the Jackpile mine.

Investigation of the distribution of transuranic radionuclides in marine sediment at the Montebello Islands, Western Australia

Three nuclear weapons tests were conducted in the 1950s at the Montebello Islands, Western Australia. The detonations were of different yields and configurations (two tower tests, one ship test), and led to substantial radionuclide contamination within the surrounding terrestrial and marine ecosystems. The region possesses great ecological and recreational significance, particularly within the marine environment. However, studies conducted so far have largely neglected the marine ecosystem which makes up the majority of the Montebello Island Marine Park and in which most test fallout would have deposited. Here we investigated the distribution of the transuranic radionuclides 238Pu, 239,240Pu and 241Am in marine sediment from the Montebello Islands. Marine sediment samples near Operation Mosaic G2 and Operation Hurricane were collected and analysed by gamma and alpha spectrometry. Activity concentrations of 239,240Pu across both series ranged from 45 to 2900 Bq kg−1, while 241Am levels ranged from 2.8 to 70 Bq kg−1. Higher activity concentrations were observed in sediment near the land-based, higher yield Mosaic G2 test, compared with the ship-based, lower yield Hurricane test. Sediment samples located closer to the detonation site were also observed to have higher activity concentrations. Radioactive particles of 0.94 mm and 1.5 mm in diameter were identified by analysis of size-fractioned sediment via investigation of 152Eu levels, photostimulated autoradiography and point gamma spectroscopy. Particles were confirmed to have transuranic radionuclide interiors, with surface coatings which were dominated by vitrified CaCO3. Their long-term resistance to weathering and subsequent persistence in the marine environment can therefore be attributed to their coated structural form. Our study confirms the persistence of transuranic radionuclides in Montebello Island marine sediment and highlights the need for additional studies to improve our understanding of the nuclear legacy in this region.

Application and Experimental Substantiation of the Radioecological Model for Prediction in Behavior 90Sr in Cultivated Soil-Crop System: A Case Study of Two Experimental Agricultural Fields.

The radioactive fission product 90Sr has a sufficient half-life (28.8 years) to be detected long after its appearance in the environment. After its uptake into the soil-edible plant system, it enters the food chain and represents a potential source of contamination that threatens human health. Due to these facts, tracking the distribution of the artificial radionuclide 90Sr in the soil-edible plant system is a subject of intense research. The tracking of the 90Sr radionuclide distribution in the soil profile, as well as in the crops on the long-term experimental fields was carried out using beta radiation spectrometry. The radiochemical analytical method was used to analyze the 90Sr content in cultivated soil and crops. The conducted study focused on the experimental substantiation of the developed model for predicting the behavior of 90Sr in the cultivated soil-crop system. The results of using the applied radioecological model for the transfer of 90Sr from the soil to the above-ground part of crops showed a relatively good agreement with the experimentally determined values of the soil-crop transfer factor, which indicates that the used model can be successfully applied for the prediction of the behavior of 90Sr in the soil-soil solution-crop system.

Nuclear power plant biological complications on marine biota from a probabilistic accident – A case study

An accident at the Barakah Nuclear Power Plant (BNPP) would result in a significant radionuclide release into the semi-closed marine environment. In this research, the released radionuclide distribution pattern and dose rate in the Persian/Arabian (Gulf) were calculated using a combined hydrodynamic/radiobiological model. Simulations of the dispersion of artificial radionuclide concentrations were conducted using a HYSPLIT model. To assess prospective hazards in case of an incident, environmental risk from ionizing contaminants: assessment and management (ERICA) tools were used. Using the Fukushima nuclear power accident as a model, the scenario source term profile was developed. The volumetric concentrations levels of pollutants ranged between 1 × 104 mBq m−3 to 1 × 1010 mBq m−3 in the radius of 200 km after 48 h. Based on the dose rates of the various marine biotas, Polychaete worms, and Pelagic fish, they had the highest and lowest dose contribution.

The effect of extracellular polymeric substances on MICP solidifying rare earth slags and stabilizing Th and U.

Microbially induced carbonate precipitation (MICP) has been used to cure rare earth slags (RES) containing radionuclides (e.g. Th and U) and heavy metals with favorable results. However, the role of microbial extracellular polymeric substances (EPS) in MICP curing RES remains unclear. In this study, the EPS of Lysinibacillus sphaericus K-1 was extracted for the experiments of adsorption, inducing calcium carbonate (CaCO3) precipitation and curing of RES. The role of EPS in in MICP curing RES and stabilizing radionuclides and heavy metals was analyzed by evaluating the concentration and morphological distribution of radionuclides and heavy metals, and the compressive strength of the cured body. The results indicate that the adsorption efficiencies of EPS for Th (IV), U (VI), Cu2+, Pb2+, Zn2+, and Cd2+ were 44.83%, 45.83%, 53.7%, 61.3%, 42.1%, and 77.85%, respectively. The addition of EPS solution resulted in the formation of nanoscale spherical particles on the microorganism surface, which could act as an accumulating skeleton to facilitate the formation of CaCO3. After adding 20 mL of EPS solution during the curing process (Treat group), the maximum unconfined compressive strength (UCS) of the cured body reached 1.922 MPa, which was 12.13% higher than the CK group. The contents of exchangeable Th (IV) and U (VI) in the cured bodies of the Treat group decreased by 3.35% and 4.93%, respectively, compared with the CK group. Therefore, EPS enhances the effect of MICP curing RES and reduces the potential environmental problems that may be caused by radionuclides and heavy metals during the long-term sequestration of RES.

Bioaccumulation and translocation of radionuclides heavy metals in Cynodon dactylon: A phytoremediation approach in Al-Dora refinery

Oil extraction methods such as fracking and drilling can disperse radioactive elements into the environment, posing potential hazards. Certain plants like Bermuda grass can combat this through rhizodegradation, a process that breaks down pollutants into harmless substances. The efficiency of this process varies by location and is influenced by factors such as soil compatibility and the presence of beneficial microbes. A study showed that Bermuda grass roots absorbed high levels of radioactive elements, especially Uranium in the soil. The distribution and concentration of these isotopes in Bermuda grass varied across different sites. For instance, Cesium-137 showed higher activity in leaves than in soil. These findings highlight the varied accumulation patterns of elements in Bermuda grass and the influence of natural radionuclide distribution on the environment. Approaches like soil amendments, microbial assistance, and genetically modified Bermuda grass can enhance rhizoremediation efficiency. Strategic planning and species selection are key to overcoming rhizoremediation challenges and enhancing its effectiveness. In addition, soil samples from the AL-Dora Refinery showed a high degree of contamination by heavy metals, with the emission from burning fuel and crude oil being the main sources. This indicates the high contamination of soil by these heavy metals. Overall, the text discusses the potential of Bermuda grass in mitigating the environmental impacts of oil extraction through rhizoremediation, and the challenges and strategies in enhancing its effectiveness. It also highlights the issue of soil contamination by heavy metals due to oil refinery emissions. This research examines the levels of heavy metal contamination in the soil of the Al-Dora refinery area, situated in central Iraq. The contamination factor (Cf) was employed to ascertain the contamination status, revealing a significant to extremely high degree of contamination by various heavy metals. The study further investigates the bioaccumulation and translocation of these heavy metals from the soil to the roots and leaves of Cynodon dactylon plants. Two methodologies were utilized to assess the role of Cynodon dactylon in soil phytoremediation: a comparison of heavy metal concentrations in plant parts with global standards, and the application of the Bioconcentration factor (BCF). The findings suggest a high potential for Cynodon dactylon to be employed in the clean-up and phytoremediation process of the contaminated soil. This presents a promising strategy towards environmental remediation in areas contaminated with heavy metals.

The characteristics of the vertical distribution of radionuclide in free troposphere from simplified release scenarios: a case study

Dose estimation in the upper air is not studied as much as on ground level or in boundary layer. However, there is a need from stakeholders in aviation industry for a reasonable estimation of the radioactive plume impact at cruising levels. This study aims to provide a quantitative estimation of the dose and how reliable it is for dispersion processes up to seven days. A Lagrangian atmospheric dispersion model is used to estimate quantitively the vertical extension of radionuclides from simplified hypothetical radionuclide release scenarios. Sources at different latitudes are selected for simulation in a boreal winter case. Three meteorological data are examined to test the sensitivity of vertical plume distribution to driving meteorological data. The vertical distribution of air concentration of radionuclides is investigated and the associated uncertainties are analysed. It is found that the vertical extension of plumes is sensitive to meteorological data being used where vertical turbulent velocities play an important role. It is therefore necessary to address the uncertainties of air concentration or dose in the free troposphere and caution must be taken when providing the results to stakeholders.

A novel equivalent model of radionuclide migration in three-dimensional rough shear fractures

Accurate prediction of radionuclide distribution in fractured rock mass is a key problem in high-level radioactive waste disposal engineering. However, it is inappropriate to directly regard rough fractures as smooth fractures when predicting radionuclide migration in real fractured rock masses. In this study, the characteristics of radionuclide migration in three-dimensional rough shear fractures are numerically analyzed considering the influence of fracture roughness, aperture distribution, contact ratios, and adsorption. Different fracture contact ratios and aperture distributions are realized by shearing two rough fracture surfaces. Based on the study, we found that the influence of surface contact is greater than that of surface roughness and aperture distribution on radionuclide migration in rough fractures with the same initial fracture aperture under laminar flow. The phenomena of dominant migration channels and low-velocity dispersion zones are observed for radionuclide dispersion in rough fractures containing contact areas. The higher the contact ratio, the more obvious this phenomenon. The breakthrough and steady state times of radionuclide are also significantly affected by the contact ratio. The higher the contact ratio, the shorter the breakthrough time, and the longer the duration from the breakthrough time to the steady state time. Adsorption delays the overall process of the radionuclide migration and prolongs the duration between the breakthrough time and the steady state time. A novel equivalent method of the radionuclide migration in rough shear fractures is proposed based on the study of radionuclide transport in rough fractures. In the proposed equivalent method, an adjustment coefficient for the transport velocity and a longitudinal dispersion coefficient for the rough fracture are defined to connect rough fractures and the corresponding smooth fractures with the same fracture aperture. The influence regularity of fracture contact and adsorption on the two defined coefficients is obtained based on over 400 numerical simulations. The specific formulas of the two coefficients are given based on the form of the analytical solution for the radionuclide transport in a smooth fracture. The dispersion coefficient and transport velocity in a rough fracture are equivalent to the dispersion coefficient and transport velocity in a smooth fracture and the fluctuation term affected by fracture surface contact and adsorption, respectively. It was verified that the equivalent model has higher accuracy, which can help characterize radionuclide migration in 3D rough fractures efficiently and precisely.

Assessment of Concentrations and Distributions of Natural Radionuclides in Soils of Abandoned Mine Sites of Jos South and Barkin Ladi in Plateau State Nigeria

Barkin Ladi and Jos South Local Government Area of Plateau State is situated in the central part of Northern Nigeria, on a rugged terrain of lowlands. It is the principal centre of tin and columbite mineralization, which forms the focal area of younger granites. The work was aimed at assessing the concentration and distribution of radionuclides in soils of abandoned tin mines and the soil’s physicochemical properties. The samples were collected in July, from five different locations in both Barkin Ladi and Jos South where mining activities were predominant. The samples were analyzed using a gamma-ray spectrometer. The result obtained reveals a range of the concentrations of 40K as 116.76 ± 0.21 to 250.15 ±0.,42 Bq/kg, 226Ra from 24.37 ± 0.31 to 90.45 ± 0.86 Bq/kg, and 232Th from 15.74 ± 0.71 to 88.43 ± 0.14 Bq/kg. The result of the physicochemical properties of the soil analyzed ranges from pH (3.12 to 6.81); organic carbon (0.01 to 1.62%); organic matter (0.22 to 3.01 %), cation exchange capacity (1.01 to 4,21Cmol/kg); clay (9.72 to 40.82 %); silt (8.32 to 40.32% and sand (32.42 to 75.38%) respectively. All the 40K results analyzed in all the sampling sites were lower than the recommended limits of 412Bq/kg, whereas most of the results of 226Ra and 232Th were above the 33Bq/kg and 45Bq/kg recommended safe limits. Exposure to elevated levels of naturally occurring radionuclides in soil can pose potential health risks to nearby populations. The physicochemical properties of the soil varied across the sampling sites. Most of the sampling sites are polluted with radionuclides and migrations of the radionuclides from the ex-mining sites to other parts of the environment were noticed from the studies conducted.