Low Uranium Concentrations Research Articles

Raw signal improvement using beam shaping plasma modulation for uranium detection in ore using laser-induced breakdown spectroscopy

Real-time quantitative detection of uranium in ores is one of the major challenges for uranium exploration. Laser-induced breakdown spectroscopy (LIBS) has been regarded as a most promising technique for this application. However, due to the matrix complexity as well as low uranium concentration of ore, the detection sensitivity of LIBS for uranium in ores is still unsatisfactory. This work explored the potential of a beam-shaping plasma modulation method to improve the limit of detection of uranium in ores. By shaping the profile of laser beam from normally Gaussian distribution to flat-top, the plasma was modulated to be more excited with reduced peak electron density at the laser-plasma interaction point for plasma shielding reduction especially at high laser energy as well as to be more morphologically stable for LIBS signal repeatability improvement. It was further found that this method enhanced LIBS signal intensity mainly by increasing the plasma temperature, while the electron density was almost unchanged, which was very attractive for uranium detection in ore since one of the major problem for uranium detection was that it is hard to find clear uranium spectral lines for analysis due to the high dense emission lines of ore samples in real cases and lower electron density, indicated less line broadening and less line overlap or interferences. A clear uranium emission line has been found in crowded ore spectra, and the intensity of U II 409.013 nm based on flat-top beam was about 5 times higher than that of Gaussian beam, and the relative standard deviation (RSD) of the signal was reduced by about 50%. Moreover, the LOD of uranium in ores was estimated to be 21.2 ppm with flat-top beam, indicating that beam shaping is a promising method for rapid and accurate detection of uranium in ores.

Natural radioactivity and its radiological implications from soils and rocks in Jaintiapur area, North-east Bangladesh.

Natural radioactivity concentrations in recent alluvial soils from swampy areas and Tertiary rocks from Jaintiapur were measured using gamma-ray spectrometer equipped with HPGe detector. The average radioactivity concentration of 226Ra, 232Th and 40K were 47 ± 6, 64 ± 5 and 762 ± 40 Bqkg−1 in soils, whereas, 25 ± 2, 37 ± 4 and 884 ± 41 Bqkg−1 in rock samples, respectively. Average radioactivity concentrations of studied soil and rock samples exceeded the world average except 226Ra for rocks. Radio-elemental ratios suggest that an oxic depositional environment with low uranium and high thorium content. Regarding radiological hazard indices, radium equivalent activities (Raeq), external hazard index (Hex) and internal hazard index (Hin) was found to be below the world permissible limits. Whereas, absorbed dose rate (D), and annual effective dose equivalent (AEDE) averages exceeded the world admissible values. Statistical studies show that radioactivity for 226Ra and 232Th linked to a source enriched in radioactive minerals and 40K related to a different sources high in K enriched minerals.

Biosorption behavior and biomineralization mechanism of low concentration uranium (VI) by pseudomonas fluorescens

Biosorption behavior and biomineralization mechanism of low concentration uranium (VI) by pseudomonas fluorescens

Uranium transfer in grasses grown on mining waste and natural soil

The transfer of radionuclides from soil to the food chain often begins with uptake by plant root system. The roots of most angiosperms showed symbiosis with arbuscular mycorrhizal fungi (AMF) and to understand the transfer process of these toxic elements it is important to consider different physical, chemical and biological factors in soils. In the present study, three grass species (Poaceae), Zea mays, Chrysopogon zizanioides and Aristida setifolia were cultivated with and without organic fertilization in experimental blocks on natural soils, at Fazenda Vargem Formosa (VF) with low uranium (U) contents in the soil, and in the leached ore deposit at the Uranium Concentrate Unit Mine (URA) in Caetité (Uraniferous Province of Lagoa Real – Brazil). In the present study, the biomass production of plants, their rate of root colonization by AMF, the levels of U in soils, roots and leaves, as well as different physico-chemical parameters related to soil fertility were evaluated. The data analysis was performed using Artificial Neural Networks (ANNs), specifically Self-Organizing Maps (SOMs). The levels of available uranium in the soil ranges from 0.33 to 1.11 mg kg−1 in VF and from 177.5 to 475.8 mg kg−1 in URA. The results revealed high percentage of root AMF colonization, even in soils with high U contents. There was an inverse relationship between soil U content and its transfer to the plant organs, with U transfer rates being influenced by plant species and not by soil parameters. C. zizanioides had the lowest transfer factor to the shoot and the highest mass productivity under conditions of high U content in soil. The results indicate that C. zizanioides is an important species for use in the recovery of U mining areas.

Assessment of metal exposure (uranium and copper) in fatty acids and carbohydrate profiles of Calamoceras marsupus larvae (Trichoptera) and Alnus glutinosa leaf litter.

Physiological changes were explored in fatty acids (FA) and carbohydrate (CHO) composition in the shredder Calamoceras marsupus larvae (Trichoptera) and leaf litter (C. marsupus food) exposed to copper and uranium under natural and experimental conditions. We measured FA and CHO content in leaf litter and larvae specimens from reference and impacted streams, and exposed for 5 weeks to four realistic environmental concentrations of copper (35 μg L-1 and 70 μg L-1) and uranium (25 μg L-1 and 50 μg L-1). Regarding FA, (1) leaf litter had a reduced polyunsaturated FA (PUFA) content in metal treatments, s (14 to 33% of total FA), compared to natural conditions (≥39% of total FA). Leaf litter exposed to uranium also differed in saturated FA (SFA) composition, with lower values in natural conditions and higher values under low uranium concentrations. (2) C. marsupus had/showed low PUFA content under Cu and U exposure, particularly in high uranium concentrations. Detritivores also decreased in PUFA under exposure to both metals, particularly in high uranium concentrations. On the other hand, (1) microorganisms of the biofilm colonizing leaf litter differed in CHO composition between natural (impacted and reference) and experimental conditions, with glucose and galactose being consistently the most abundant sugars, found in different amounts under copper or uranium exposure; (2) CHO of detritivores showed similar high galactose and fucose concentrations in contaminated streams and high copper treatments, whereas low copper treatment showed distinct CHO profiles, with higher mannose, glucose, arabinose, and fucose concentrations. Our study provides evidence of metal exposure effects on FA and CHO contents at different trophic levels, which might alter the quality of food flow in trophic webs.

Uranium in Source Rocks: Role of Redox Conditions and Correlation with Productivity in the Example of the Bazhenov Formation

The paper reports comprehensive analysis of different factors affecting uranium content in oil source rocks and the relationship between uranium content and productivity of source rocks. The analysis of data for 13 wells of the Bazhenov Formation (Western Siberia, Russia) was carried out. The uranium content of the rocks was measured by gamma-ray spectrometry on core samples. In order to analyze factors affecting uranium accumulation in source rocks, we studied content and characteristics of organic matter (Rock-Eval pyrolysis), and also mineral, element, and isotope composition of rocks. We have shown that redox conditions at the sedimentation stage have the most pronounced impact on the uranium accumulation in the rocks of the Bazhenov Formation. It was also shown that productive intervals, containing increased amounts of mobile hydrocarbons, are characterized by low (<20 ppm) concentration of uranium. However, the intervals, containing phosphorite minerals may show better reservoir properties and oil saturation at higher concentration of uranium. The analysis of correlations and relationships between uranium content and Rock-Eval pyrolysis indexes (oil saturation index and productivity index) enabled formulation of criteria for selection of oil-saturated intervals using the spectral gamma and pulsed neutron spectroscopy log data.

Determination of 238U and 40K Radionuclide Concentrations in Some Granite Rocks by Gamma Spectroscopy and Energy Dispersive X-ray Analysis.

Uranium-238 (238U) and potassium-40 (40K) are important naturally occurring radionuclides. Gamma spectroscopy is a direct, non-destructive method used to determine radionuclide concentrations, but it suffers from the interference of gamma lines. 40K gamma spectroscopy is affected by background interference, which leads to a reduction in the minimum detectable activity. The energy dispersive X-ray analytical technique is quick, with fewer interference problems or background effects. However, it is an indirect method for calculating and deducing the concentrations of isotopes. The aim of the present study was to compare and evaluate both techniques so that they can be utilized efficiently. The results of 238U and 40K were measured by well-calibrated gamma spectroscopy and energy dispersive X-ray techniques. the results indicated that Halayeb White granite is the most environmentally safe compared to the other two types because it contains a very low concentration of uranium 238 and potassium 40.

Enrichment of uranium in seawater by glycine cross-linked graphene oxide membrane

Extraction of uranium from seawater can satisfy the request for uranium in the field of sustainable nuclear power generation. However, direct extraction of uranium from seawater with traditional methods encounters many difficulties with reduced efficiency because of the extremely low uranium concentration. Based on the hydration diameter difference between uranium and the main coexisting ions (K+, Na+, Ca2+ and Mg2+), membrane separation technology is thought as an effective way to enrich uranium in seawater. Here, a new type of glycine (Gly) cross-linked graphene oxide (GO-Gly) membrane was fabricated, whose interlayer spacing (d) is very stable with uniform channel size satisfied the requirement for uranium enrichment. The respectively single ion rejection properties of uranium and the main coexisting ions in seawater revealed that ∼ 100% of uranium was rejected by the GO-Gly membrane. In addition, the excellent uranium rejection property of this membrane can be maintained in continuously filtrating the simulated seawater, only uranium ion was obviously enriched but the concentrations of the main coexisting ions kept nearly constant. The distinct rejection and enrichment properties of uranium ions by GO-Gly membrane made it an ideal candidate for uranium enrichment in seawater.

Anti-biofouling bio-adsorbent with ultrahigh uranium extraction capacity: One uranium resource recycling solution

Uranium extraction from seawater is an effective solution to the shortage of uranium resources on land. However, because of the high salinity in seawater, an extremely low uranium concentration (~3.3 ppb) and biofouling caused drastically decrease the performance of adsorbents, and the practical development of uranium extraction from seawater still faces major challenges. Here, we demonstrated a simple strategy to utilize waste feather fiber (FF) to prepare anti-biofouling amidoxime functionalized FF (FF-Cu2O/AO), which was applied to the extraction uranium from seawater. The introduction of Cu2O endows FF-Cu2O/AO with anti-biofouling and enhances the binding of uranyl ions to amidoxime. FF-Cu2O/AO exhibited outstanding uranium adsorption performance, adsorbing 816 mg-U/g-Ads from 8 ppm uranium-spiked water. Following immersion in natural seawater for 30 days, the uranium extraction capacity of FF-Cu2O/AO reached 7.73 mg-U/g-Ads. More importantly, the strategy can be used for the preparation of other uranium adsorbents based on amidoxime functionalized polymer fibers to provide antibacterial and improved adsorption performance. Economic analysis shows that the cost of FF-Cu2O/AO adsorption of uranium from natural seawater is much lower than that of conventional adsorbents. Therefore, FF-Cu2O/AO would be an outstanding candidate for extracting uranium from seawater because of its high uranium extraction capacity, anti-biofouling and low-cost.

Pyrolysis of animal manure under nitrogen atmosphere: An environment protection way to obtain animal manure biochar for high-efficient adsorption of uranium (VI)

For reducing the damage of pig manure (PM) to the ecological environment, three different biochar materials were prepared by pretreating PM with different reagents (distilled water, hydrochloric acid and sodium hydroxide). It was found that the oxygen content of PMBC-OH- reached 34.4%, which was much higher than that of PMBC (21.1%) and PMBC-H+ (14.1%), indicating that the oxygen-containing functional groups onto PMBC-OH- were abundant. Further, the adsorption properties of the three kinds of biochars were discussed with uranium (VI) as the adsorbate. Compared with PMBC (369.9 mg/g) and PMBC-H+ (53.3 mg/g), PMBC-OH- possessed excellent performance and its adsorption capacity reached 952.5 mg/g, which was much higher than that of other reported biochar materials. Meanwhile, PMBC-OH- could completely remove uranium (VI) from solution with low uranium (VI) concentration to achieve the standard of wastewater discharge. Briefly, the method of preparing biochar by pretreating PM with sodium hydroxide could effectively improve the utilization rate of PM and reduce the damage of nutrients in PM to ecological environment. Based on the above analysis, PMBC-OH- possessed the potential to be applied for removing uranium (VI) from wastewater.

Waste feather fiber based high extraction capacity bio-adsorbent for sustainable uranium extraction from seawater

Recycling uranium from seawater is of great significance to the development of nuclear industry. However, due to high salinity and low uranium concentration in seawater, there are still many challenges in current seawater uranium extraction technology. In this study, waste feather fibers (FF) were used as raw materials to develop a phosphonate-functionalized feather fiber (FF-PT). The study on the adsorption performance shows that FF-PT have good adsorption and recycling performance for uranium. The study on the adsorption performance shows that FF-PT have good adsorption and recycling performance for uranium. The adsorption capacity reaches up to 342.5 mg·g−1 in the 8 ppm uranium solution, and service life of at least 10 cycles were obtained. In addition, in the environment with high salinity and the coexistence of metal competitive ions, FF-PT also shows excellent selectivity, and it can reach 3.22 mg·g−1 adsorption capacity after immersed in natural seawater for 30 days. Combined with the results of economic analysis, we believe that the FF-PT has broad application prospects in the industrialized uranium extraction from seawater.

Reactive transport modeling of U and Ra mobility in roll-front uranium deposits: Parameters influencing 226Ra/238U disequilibria

Uranium reserve estimates in ore deposits can be significantly impacted by 226Ra/238U disequilibria arising from the differential mobility of uranium and radium during groundwater transport. 1D reactive transport models were developed to investigate the long-term effects of retention processes (UO2(am) precipitation, U(VI) and Ra sorption on smectite, Ra co-precipitation with barite) on the repartitioning of 238U and 226Ra during formation of roll-front type deposits. Analytical solutions to radioactive decay chains were used in complement to examine the influence of geochemical parameters, including fluid 234U/238U activity ratios and α-recoil loss, on 226Ra/238U disequilibria in uranium ores. Model results demonstrate that smectite and barite can produce 226Ra/238U ratios >1 at low uranium contents and may explain 226Ra/238U disequilibria occurring in altered rock up- and downstream of roll-front deposits. The capacity of these phases to take up Ra and generate 226Ra/238U disequilibria depends on both mineral contents and groundwater compositions, and is thus expected to be site-specific. Simulations of ore deposits that advance downstream with time demonstrate the formation of stronger 226Ra/238U disequilibria, as expected, in the downgradient side or nose of the ore, reflecting both younger mineralization ages and the presence of active uranium precipitation. Whether disequilibria are positive or negative with respect to secular equilibrium, however, depends on the 234U/238U activity ratio in the fluid from which uranium minerals precipitate. Smaller hydraulic conductivities are shown to generate a narrower range in 226Ra/238U activity ratios with distance, and may explain the occurrence of disequilibria in the limb ore that are less pronounced than those in the nose. Furthermore, the ability of α-recoil loss to decrease 226Ra/238U activity ratios at secular equilibrium may account for negative disequilibria in high grade ores. The South Tortkuduk uranium deposits (Kazakhstan) are subsequently used as a case study to identify the processes and parameters that may contribute to 226Ra/238U disequilibria at this site. Variations in multiple parameters, including clay contents, barite contents, and mineralization ages, are found to reproduce measured 226Ra/238U activity ratios in the roll-front ore. Prioritization of these parameters will necessitate field measurements targeting both groundwater fluids and the host rock. Results from this study will ultimately aid geologists in building appropriate hydrogeochemical data sets to more efficiently locate and exploit uranium ore deposits.

Two-Dimensional Imprinting Strategy to Create Specific Nanotrap for Selective Uranium Adsorption with Ultrahigh Capacity

Uranium extraction is highly challenging because of low uranium concentration, high salinity, and a large number of competing ions in different environments. The template strategy is developed to address the defect of poor selectivity, but the adsorption capacity is limited by cavity blocking during the preparation of materials. Herein, a two-dimensional (2D) imprinting strategy is adopted to design 2D imprinted networks with specific nanotraps for effective uranium capture. The imprinted networks are established through the condensation polymerization of uranyl complexes, which are formed by aromatic building units coordinating with uranyl ions on the equatorial plane. Different from traditional imprinting materials that contain many invalid cavities (buried cavities or unreleased cavities), the as-prepared adsorbents possess tailored 2D nanotraps, which are open and specific to uranyl. Thus, the optimized networks not only show excellent selectivity for uranium (Kd = 964,500 mL/g in multi-ion solution) and slight disturbance of high salinity but also possess an ultrahigh adsorption capacity of 1365.7 mg/g. In addition, this adsorbent shows a high extraction efficiency for uranium under a wide range of pH conditions and exhibits good regeneration performance. This work proposes a pioneering strategy of 2D imprinting networks to capture uranium specifically with high capacity and can be applied to material design in many other fields.

Uranium removal from waste water of the tailings with functional recycled plastic membrane

Plastic pollution has become one of the most pressing environmental issues. Meanwhile, developing highly efficient adsorbents for uranium removal from the wastewater of its tailings is also of great significance in environmental protection. In this study, wastes of the plastic membrane in daily life were recycled and functionalized to treat uranium pollution in the environment. Membrane adsorbent with amidoxime (AO) group was successfully prepared using recycled plastic membranes through two-step polymerization. A network of nano-holes and nanostructured particles were observed on the surface of the AO modified membrane (AO-membrane) adsorbent. The adsorption performances from uranium solution and uranium tailings wastewater were evaluated in batch and column adsorption experiments. AO-membrane exhibited good removal performance in a wide pH range from 2 to 8. After adsorption in uranium tailings wastewater, the equilibrium concentrations of uranium in solution were lower than 50 μg/L, meeting the national standard of uranium solution discharge (50 μg/L). AO-membrane could reach adsorption equilibrium within 5 h in uranium tailings wastewater and present uranium removal ratio of nearly 100%. These indicated that this AO-membrane could be used for deep purification of wastewater, especially with low uranium concentration. AO-membrane exhibited a remarkable reuse performance and long service life. During the 10 cycles of adsorption and desorption, AO-membrane exhibited almost 100% uranium removal ratio even after ten adsorption and desorption cycles. This work provides new insights into the technology of waste control by waste.

A Membrane‐Supported Bifunctional Poly(amidoxime‐ethyleneimine) Network for Enhanced Uranium Extraction from Seawater and Wastewater

Uranium extraction from natural seawater and wastewater are quintessential requirements to supply uninterrupted carbon-free nuclear energy and to prevent potential radiochemical and toxicological effects, respectively. Owing to the complexity and low-concentration uranium of these water samples, the design and synthesis of sorbent materials for uranium extraction with meaningful efficiencies remains a grand challenge. Herein, we reported a novel three-dimensional bifunctional network of hyperbranched poly(amidoxime-ethyleneimine) (PAO-h-PEI) using PEI as the skeleton material via cyanoethylation, crosslinking and then amidoximation. As a result of the synergistic supramolecular strategy, the PAO-h-PEI membrane achieved a remarkable adsorption capacity of 985.7 mg/g for aqueous uranium solution, which was 2.5 folds that of the monofunctional h-PEI membrane (387.6 mg/g). The PAO-h-PEI membrane also exhibited good selectivity towards uranium in the presence of various metal ions, high-content salt, and natural organic matter as well as common anions. According to the XPS and FTIR results, the utilization of amines as the second ligand enhanced uranyl binding by providing additional coordination sites or by interacting with oxime to force N-OH dissociation. The good reusability (adsorption rate of 93% after six adsorption-desorption cycles) and satisfactory adsorption performance in extracting low-concentration uranium in real seawater demonstrate its practicability.

Metal-free 2D/2D C3N5/GO nanosheets with customized energy-level structure for radioactive nuclear wastewater treatment

How to efficiently treat radioactive uranium-containing nuclear wastewater is one of the significant challenges to ensure the safety of nuclear technology and to avoid environmental pollution. Here we firstly prepare the metal-free 2D/2D C3N5/GO nanosheets, and customize a type-II heterojunction based on the band bending theory to achieve enhanced uranium extraction capacity via synergistic adsorption photoreduction engineering. The structure of C3N5 is explained by electron energy loss spectroscopy and synchrotron-based near-edge X-ray absorption fine structure. And C3N5 with larger π-conjugated structure expands the light response range to 747 nm, which is about 1.67 times that of C3N4. Further, we also use density functional theory to prove the existence of alternating energy levels so that photogenerated electrons could be continuously injected into the surface of GO to ensure the effective separation of electron-hole pairs and increase the material activity. The results show that the removal ratio of uranium by 2D/2D C3N5/GO heterojunction is achieved as high as 96.1% even at a low uranium concentration of 10 ppm, and reached 93.4% after exposure to gamma-ray. This work will lay a foundation for customizing the energy band structure of nonmetal-based 2D/2D nanohybrids and enriching uranium-containing wastewater through adsorption photoreduction engineering in the future.

قدرت تأثیر یک مقاله روزنامه بر حل مشکلات زیستی جهانی

قدرت تأثیر یک مقاله روزنامه بر حل مشکلات زیستی جهانی

Covalent modification of ZIF-90 for uranium adsorption from seawater

Uranium is one of the main crude materials for nuclear reaction, but the total uranium content on land is far from meeting the long-term needs of nuclear energy for the human being. How to enrich uranium from seawater with high reserves but extremely low uranium concentration and a great quantity of competitive ions has become a key project. In this work, we report the synthesis of aminooxime functionalized ZIF-90 by grafting 4-aminobenzamidoxime, named ZIF-90-ABOA , which exhibits outstanding adsorption performance benefitting from the high chelating ability of amidoxime towards uranium. The maximum adsorption capacity of uranium is 353.4 mg g −1 from aqueous solution, which is much higher than the original ZIF-90 . Additionally, the adsorption capacity can reach 2.8 mg g −1 in 7 days from natural seawater, proving the potential enrichment of uranium in real application. Aminooxime functionalized ZIF-90 was successfully synthesized by covalent modification, which can efficiently extract uranium from natural seawater. • ZIF-90 was functionalized by 4-aminobenzamidoxime groups via covalent modification. • Functionalized ZIF-90 shows superior adsorption performance compared with pristine one. • Functionalized ZIF-90 demonstrates a good prospect in real seawater application.

Constructing new Fe3O4@MnOx with 3D hollow structure for efficient recovery of uranium from simulated seawater

Enrichment of uranium from seawater is a promising method for addressing the energy crisis. Current technologies are generally not effective for enriching uranium from seawater because its concentration in seawater is low. In this study, new Fe3O4@MnOx with 3D hollow structure, which is capable of enriching low concentration uranium, was prepared via a novel redox etching method. The physicochemical characteristics of Fe3O4@MnOx were studied with TEM, HRTEM, SEAD, FTIR, XRD, and N2 adsorption-desorption analysis. Dynamic kinetic studies of different initial U(VI) concentrations revealed that the pseudo-second-order model fit the sorption process better, and the sorption rates of Fe3O4@MnOx in 1, 10, and 25 mg/L U(VI) solution were 0.0124, 0.00298, and 0.000867 g/mg·min, respectively. Isothermal studies showed that the maximum sorption amounts were 50.09, 56.27, and 64.62 mg/g for 1, 10, and 25 mg/L U(VI), respectively, at pH 5.0 and 313 K, suggesting that Fe3O4@MnOx could effectively enrich low concentration U(VI) from water. The sorption amount of U(VI) did not significantly decrease in the presence of Na+, Mg2+, and Ca2+. HRTEM, FTIR, and XPS results demonstrated that Fe(II) and Mn/Fe–O–H active sites in Fe3O4@MnOx were accounted for the high and specific enrichment efficiency. A column experiment was conducted to evaluate the U(VI) sorption efficiency of Fe3O4@MnOx in simulated seawater. The U(VI) sorption efficiency remained above 80% in 28 days run. Our findings demonstrate that Fe3O4@MnOx has extraordinary potential for the enrichment of uranium from simulated seawater.

First U-Pb dating of fossilized soft tissue using a new approach to paleontological chronometry

Abstract Previous U-Pb dating of fossils has had only limited success because of low uranium content and abundance of common Pb as well as element mobility during late diagenesis. We report the first accurate U-Pb dating of fossilized soft tissue from a Pliocene phosphatized bivalve mold using laser ablation–inductively coupled mass spectrometry (LA-ICPMS). The fossilized soft tissue yields a diagenetic U-Pb age of 3.16 ± 0.08 Ma, which is consistent with its late Pliocene stratigraphy and similar to the oldest U-Pb age measured on accompanying shark teeth. Phosphate extraclasts give a distinctly older age of 5.1 ± 1.7 Ma, indicating that they are likely detrital and may have furnished P, promoting phosphatization of the mold. The U-Pb ages reported here along with stratigraphic constraints suggest that diagenesis occurred shortly after the death of the bivalve and that the U-Pb system in the bivalve mold remained closed until the present. Shark teeth collected from the same horizon show variable resetting due to late diagenesis. Data were acquired as line scans in order to exploit the maximum Pb/U variation and were regressed as counts, rather than ratios, in three-dimensional space using a Bayesian statistical method.