High Uranium Content Research Articles

Efficient Functionalization of Polyethylene Fibers for the Uranium Extraction from Seawater through Atom Transfer Radical Polymerization

Brush-on-brush structures are proposed as one method to overcome support effects in grafted polymers. Utilizing glycidyl methacrylate (GMA) grafted on polyethylene (PE) fibers using radiation-induced graft polymerization (RIGP) provides a hydrophilic surface on the hydrophobic PE. When integrated with atom transfer radical polymerization (ATRP), the grafting of acrylonitrile (AN) and hydroxyethyl acrylate (HEA) can be controlled and manipulated more easily than with RIGP. Poly(acrylonitrile)-co-poly(hydroxyethyl acrylate) chains were grown via ATRP on PE-GMA fibers to generate an adsorbent for the extraction of uranium from seawater. The prepared adsorbents in this study demonstrated promise (159.9 g-U/kg of adsorbent) in laboratory screening tests using a high uranium concentration brine and 1.24 g-U/kg of adsorbent in the filtered natural seawater in 21 days. The modest capacity in 21 days exceeds previous efforts to generate brush-on-brush adsorbents by ATRP while manipulating the apparent surface hydr...

The uranium content in Dictyonema shale of the Kaibolovo–Gostilitsy Area in the Baltic basin (Leningrad Region)

This paper reports the data on the uranium content in Dictyonema shale and phosphate rock in the Kaibolovo–Gostilitsy Area of the Baltic Basin (Leningrad Region). Specific features of the uranium ore in the studied area and stratigraphic rock sequence of the Early Ordovician Pakerort horizon are considered. A high uranium concentration in the Dictyonema shale layer has been determined, the correlation of uranium with other elements was defined, probable conditions of uranium ore genesis are described, and predicted uranium resources within the studied area are estimated.

Uranium of dictyonema shale of Kajbolovo-Gostilitsky area of Baltic basin (Leningrad region)

The results of researches on uranium of Dictyonema shale of the Kajbolovo-Gostilitsky area of Baltic basin of shale and phosphorites (Leningrad region) are presented. Features uranium ore on the area and in sedimentary rock sequence of Pakerort horizon of early Ordovician Period are revealed. High concentrations of uranium in a layer of Dictyonema shale are determined, correlation of uranium with other elements are defined, probable conditions uranium ore genesis are described, look-ahead resources of uranium within the limits of the studied area are estimated.

Delineating hazardous material without touching — AEM mapping of Norwegian alum shale

Alum shale is a particular type of metamorphic clay that occurs in Cambro-Ordovician metasediment units throughout southern Scandinavia. Owing to its geochemical composition, it is considered a large environmental challenge in Norway (Endre and Sormo, 2015) and poses a significant site hazard for infrastructure projects (Endre, 2014). Swedish alum shale has such a high Uranium content, that is was mined as a Uranium ore during the mid-1900s (Dyni, 2006). Norwegian alum shale typically contains more than 15 g/kg sulphides and 60-200 mg/kg Uranium. It is consequently a source for radon gas posing a risk to human health. The sulphides oxidize to produce sulphuric acid with pH down to 2-1 once the shale is exposed to air and water, posing a hazard to concrete and metal constructions and the environment. Finally, the most critical geotechnical risk connected to alum shale is its intense swelling owing to oxidation that has damaged properties in the vicinity of building sites that exposed alum shale units and consequently initiated swelling. Prior knowledge of the existence and extent of this hazardous shale is consequently a major risk management factor for underground building activities in areas prone to alum shale. The state of practice for identifying alum shale and other acid producing black shales classified by the Norwegian Environment Agency (Endre and Sormo, 2015), is primarily based on geochemistry and an understanding of the local geology. Geochemical identification is based on the balance between acidification- and neutralisation potential (Pabst et al., 2016) the geological risk for projects in alum shale prone areas is consequently high. In the worst case, a project may have to be abandoned, for example if the excavated shale volume exceeds the capacity of special waste landfills in the area. Geophysical delineation can decrease the geological risk and increases the efficiency of detailed volume assessments. Since 2014, we have been studying how sulphide and uranium content of various black shale types relate to electrical properties. Sulphide-rich alum shale has very low resistivity (~0.1 Ωm) (Lysdahl et al., 2015) and a strong induced polarization signature (Lysdahl et al., 2016). In the following we show the relationship between geochemically classified shale types and resistivity measurements directly on drill cores as well as surface electrical resistivity tomography (ERT) data. Two case histories show black shale units even at depths exceeding 80 metres based on airborne electromagnetic (AEM) surveying. Here we only focus on resistivity, for further studies on the polarization behaviour of alum shale please see Bazin et al. (2015) and (2017).

Genesis of tuff interval and its uranium enrichment in Upper Triassic of Ordos Basin, NW China

Recently measured high gamma ray values in the Yanchang Formation of the Upper Triassic in the Ordos Basin have added an interesting and controversial twist to the study of the formation’s uranium enrichment and genesis. High uranium and thorium contents in the tuffaceous layer cause high gamma ray values in the Yanchang Formation. Petrographic studies, major elements, rare earth elements (REEs), and trace elements have been systematically analyzed to determine the composition, geochemical environment, and diagenetic processes of the layer. The observed color of the tuffaceous layer in the study area varies from yellow to yellowish brown. The tuff consists of matrix supported with sub-rounded to sub-angular lithic fragments. These lithic fragments probably derived from pre-existing rocks and incorporated into the tuffaceous layer during volcanic eruption. Quartz, plagioclase, and biotite were observed in well to poorly sorted form, in addition to framboidal pyrite and organic laminae. Measured ratios of SiO2/Al2O3 ranged from 3.277 to 6.105 with an average of 3.738. The ratio of TiO2/Al2O3 varied from 0.037 to 0.201 with an average of 0.061, indicating that the sediments of the tuffaceous layer originated from an intermediate magma. REE distribution patterns show sharp negative Eu anomalies, indicating a reducing environment, which is suitable for uranium deposition. A reducing environment was confirmed by black shale in the base of the Yanchang Formation. Such black shale has high organic matter content that can take kerogene from mudstone and provide a reducing environment for uranium enrichment in the tuffaceous layer. Moreover, negative Eu anomalies and the REE patterns indicate a subduction-related volcanic arc environment as the magma source of the tuffaceous layers. High values of Rb, Ba, and Sr might be the result of fluid phase activities; low values of Hf and Eu indicate the involvement of crustal material during diagenesis of the tuff. Discrimination diagrams (Th/Yb vs Ta/Yb, Th/Hf vs Ta/Hf) suggest an active continental margin as the tectonic setting of source volcanoes. Plots of Nb versus Y, Rb versus Y + Nb, TiO2 versus Zr, and Th/Yb versus Nb/Yb of the tuffaceous content point to calc-alkaline continental arc-related magmatism. We concluded that uranium enrichment in the tuffaceous layer was supported by oxidation–reduction.

Uraniferous dolomite: a natural source of high groundwater uranium concentrations in northern Bavaria, Germany?

Naturally high uranium (U) concentrations occur in the groundwater of northern Bavaria (southeastern Germany) although the source(s) and geochemical processes controlling its occurrence are poorly understood. An earlier study identified the weathering of uraniferous apatite as responsible for elevated groundwater U in a part of the region. This present study focuses on a uraniferous dolomite facies in the Triassic sandstone aquifer of northern Bavaria as a potential source of dissolved uranium in the regional groundwater. Hydrogeochemical and mineralogical analytical methods (INAA, ICP-OES, SEP, XRD, C/S measurements), in conjunction with existing hydro- and geochemical datasets, as well as hydrogeochemical modeling approaches indicate a strong connection between groundwater U and the dolomitic facies. Highest groundwater concentrations (max 58.3 µg L−1) occur under slightly alkaline and oxic to slightly reducing conditions. Uranium speciation is dominated by mobile U(VI), predominantly in the form of uranyl-carbonate complexes. Groundwater is undersaturated with respect to U mineral phases. In addition, high values in the dolomite extraction step (SEP) and a positive correlation of dolomite (XRD) and Ca with U (INAA) support the assumption of mobilization from the uraniferous dolomite as a potential source for elevated U concentrations, and hence one of the causes for the geogenic groundwater U problem in this region.

Ground gamma-ray spectrometric studies of El-Sahu area, southwestern Sinai, Egypt

Based on the previous airborne gamma-ray spectrometric study carried out in southwestern Sinai area, El Sahu area was selected for detail ground gamma-ray spectrometric survey. This area is considered as a good target for radioactive mineral exploration. The study area is exposed in a Paleozoic basin covered by different rocks (ranging from Precambrian to Quaternary). The ground gamma-ray spectrometric survey has been conducted along the study area through random survey. The resultant gamma-ray spectrometric maps show different levels of radioactivity over the studied area, which reflect contrasting radioelement contents for the exposed various rock types. The studied area possesses total count ranging from 2.6 to 326 Ur, 0.1 to 2.8% K, 1.7 to 316ppm eU and 0.9 to 47.5ppm eTh. The highest uranium concentrations are located in the northern and southern parts of El Sahu area. They are mainly associated with Um Bogma Formation occurrences.Uranium ratio maps (eU/K and eU/eTh) as well as ternary maps show sharp increase of eU content over both potassium and thorium contents associated with the ENE and NNW trends in Um Bogma Formation, indicating an increase in the U-potentiality than the surrounding rocks. This indicates that the mineralization in the study area may be structurally-controlled.

Radiation dose-dependent risk on individuals due to ingestion of uranium and radon concentration in drinking water samples of four districts of Haryana, India

ABSTRACTUranium gets into drinking water when the minerals containing uranium are dissolved in groundwater. Uranium and radon concentrations have been measured in drinking water samples from different water sources such as hand pumps, tube wells and bore wells at different depths from various locations of four districts (Jind, Rohtak, Panipat and Sonipat) of Haryana, India, using the LED flourimetry technique and RAD7, electronic silicon solid state detector. The uranium (238U) and radon (222Rn) concentrations in water samples have been found to vary from 1.07 to 40.25 µg L−1 with an average of 17.91 µg L−1 and 16.06 ± 0.97 to 57.35 ± 1.28 Bq L−1 with an average of 32.98 ± 2.45 Bq L−1, respectively. The observed value of radon concentration in 43 samples exceeded the recommended limits of 11 Bq L−1 (USEPA) and all the values are within the European Commission recommended limit of 100 Bq L−1. The average value of uranium concentration is observed to be within the safe limit recommended by World Health Organization (WHO) and Atomic Energy Regulatory Board. The annual effective dose has also been measured in all the water samples and is found to be below the prescribed dose limit of 100 µSv y−1 recommended by WHO. Risk assessment of uranium in water is also calculated using life time cancer risk, life time average daily dose and hazard quotient. The high uranium concentration observed in certain areas is due to interaction of ground water with the soil formation of this region and the local subsurface geology of the region.

Spatial distribution of uranium in mice kidneys detected by laser ablation inductively coupled plasma mass spectrometry.

The aim of the study is to better understand where uranium deposits in mice kidneys. The spatial distribution of uranium was examined in the kidneys of C57BL/6 mice using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Mice were exposed to varying levels of uranyl nitrate in their drinking water. Calibration standards were developed to allow for semi-quantitative measurement of uranium in the cortical and medullary regions of mice kidney by LA-ICP-MS. Scanning electron microscopy was used to image the ablation patterns on the kidney. Uranium levels were observed to increase in kidney tissue as uranyl nitrate treatment exposure levels increased. A trend towards a higher uranium concentration in the medullary versus cortical region of the kidneys was observed. These results show the usefulness of LA-ICP-MS in toxicity studies by providing a quantitative, spatial assessment of uranium deposition in a target organ.

Radioactive Occurrence in Sediments of Cenozoic Age near Bandha Village, Jaisalmer District, Rajasthan

ABSTRACT The radioactivity is dependent on the isotope and their concentration in the mineral such as potassium (K), uranium (U) and thorium (Th). In this paper the presence of a 3 to 5 m thick uranium and thorium bearing sediment of Cenozoic age is reported above Goru Formation of Jaisalmer basin. Gamma ray log response of Well-1 which falls under the study area has marked with very high GR (gamma ray) readings ranging from 350-1488 API coupled with high uranium and thorium content from spectral gamma ray log ranging from 92-178 ppm and 60-80 ppm respectively at the depth of 50 m from ground surface (-110m above MSL). Further studies are required to delineate the lateral thickness variation for mining purpose which may be a radioactive source.

Radionuclides in groundwater, rocks and stream sediments in Austria – results from a recent survey

Abstract In 2014, the Geological Survey of Austria (GBA) published – in cooperation with further national institutions – an overview map on radionuclides in groundwater, rocks and stream sediments at a scale of 1:500 000 with explanatory notes. In the frame of this activity, the uranium, 228 Ra, 226 Ra, 222 Rn, 210 Pb and 210 Po analyses in groundwater studies made by the Austrian Agency for Health and Food Safety (AGES) and Environment Agency of Austria (Umweltbundesamt), as well as the uranium and thorium analyses of stream sediments of the GBA and whole-rock analyses from different sources, were evaluated statistically. Furthermore, the GBA's comprehensive airborne radiometric data were exploited. The aim of this study was to work out typical spectra of the radionuclide content in the groundwater and aquifers of different geological settings. It appeared that the concentration of 222 Rn in groundwater depends significantly on the uranium content of the aquifer. In contrast to this, the other radionuclides in groundwater did not show a clear correlation with uranium and thorium in the subsurface geology. Concerning 228 Ra, 226 Ra, 210 Pb and 210 Po, the lack of relationship to the subsurface composition seems to be a result of the low concentrations in groundwater. With respect to uranium in groundwater, there is a mixed situation: on the one hand, high uranium concentrations in groundwater can be observed in the Alps in regions with uranium bearing orthogneisses. On the other hand, in sediment basins of NE Austria where the underlying geology contains little uranium. Whether this is caused by special geological features combined with the given low precipitation or by the extensive agriculture (uranium from phosphate fertilizer) is under examination. Concerning the threshold values of the radionuclides in groundwater (radiation), no exceedance could be observed. In spite of this, the concentration of the heavy metal uranium sometimes exceeded the threshold value of 15 µg l −1 : this is especially true for the regions mentioned above. In addition, an attempt was made to compare the Austrian values with data from neighbouring countries. It became clear that only a few published datasets exist that are comparable. Radon analyses of soil gas in the Czech Republic and Bavaria show the same geological patterns as the Austrian radon analyses of the groundwater. In addition, to enable the reader to compare the Austrian data with datasets from other countries, additional tables are included here for all types of data. They show the statistic distributions of different geological classes in a coordinated way.

Economically viable rare earth element deposits along beach placers of Andhra Pradesh, eastern coast of India

A comprehensive study was carried out in order to determine the radioelement and rare earth element (REE) concentrations in beach placer deposits at selected locations along the eastern coast of Andhra Pradesh in India. This was done to evaluate the economic value of these deposits. The findings of this study suggest that high Th and low K concentrations delineate the prospective regions having REE deposits. The beach placers, in general, can be characterized by high thorium and moderate uranium concentrations. The concentrations of REEs vary in the following order: Ce > La> Nd > Pr > Sm > Gd > Dy. Rapid in situ thorium prospectivity coupled with laboratory-based techniques like ICP-MS, as proposed in this study, would help in the identification of prospective REE sources along the coastal placers. The development of indigenous resources of light rare earth elements (LREEs), medium rare earth elements (MREEs), and heavy rare earth elements (HREEs) would decrease the dependence on imports, which have a strategic hold on the production and supply of the REEs, globally.

Uranium mineralization in the Alum Shale Formation (Sweden): Evolution of a U-rich marine black shale from sedimentation to metamorphism

The Alum Shale Formation is a metal-rich black shale, deposited on the Baltoscandian platform between Middle Cambrian and Early Ordovician. These black shales may be of particular economic interest for their relatively high uranium content (100–300ppm) and their wide distribution from Norway to Estonia. Scandinavian Alum Shale may thus constitute a great potential resource of uranium, as a low grade ore. The Alum Shale Formation is particularly interesting to study the mineralogical expression and content of uranium in series submitted to progressive burial and metamorphism. For this purpose, the behavior of U, P, Ti and organic matter was studied on a series of representative samples from most Alum Shale prospection zones. In southern Sweden, where Alum Shale underwent fairly shallow burial, uranium concentrations have no mineralogical expression except a rather high U content of biogenic phosphates. Calcite concretions (beefs) and fractures recorded the migration of hot overpressured hydrocarbons and brines from thermally mature areas to immature Alum Shale. However, thermal maturation and fluid migration did not allow remobilization of uranium and metals. At the opposite, in northern Sweden, where the series were folded, duplicated and submitted to low grade Greenschist metamorphism during Caledonian orogeny, phospho-silicates U-Si-Ca-P (±Ti ±Zr ±Y) and minor amounts of uraninite are identified and indicate that U, P, and Ti were mobile and precipitated as new phases. The effect of metamorphism is therefore important to consider as the leachability of U, especially during (bio)-hydrometallurgical processes, which will be by far different between the two considered areas.

Radioactivity of Soil, Rock and Water in a Shale Gas Exploitation Area, SW China

Studies have been carried out to investigate the baseline radioactivity level (gross alpha, gross beta and 226Ra) of soil, rocks and groundwater in the Fuling block, Chongqing, the largest shale gas exploitation area of China. The results show that there is a general activity concentration trend of gross alpha, gross beta and 226Ra: shale > soil > limestone due to the high content of uranium, thorium and potassium in shale and low content in limestone. The average activities of shallow groundwater from a limestone aquifer are 0.14, 0.13 and <0.008 Bq/L for gross alpha, gross beta and 226Ra, respectively. The radioactivity concentrations of gross alpha, gross beta and 226Ra (4.37, 1.40 and 0.395 Bq/L, respectively) of the formation water were far lower than those of formation water in the Marcellus shale in the USA (with ranges of 86–678, 23–77 and 16–500 Bq/L, respectively). One polluted shallow groundwater source and its associated stream sediments had been polluted due to leakage of drilling fluid with relatively high radioactivity levels and high concentration of main ions. Overall, this study provides an important baseline radioactivity level to assess the impact of shale gas exploitation on a shallow environment.

Hydrogeotoxicity from arsenic and uranium in the southern Duero Basin, Spain

In the southern part of the Cenozoic Duero Basin (Spain), naturally occurring arsenic and uranium in groundwater sometimes occur in concentrations exceeding the limits for potable water. Usually, concentrations of these elements are only slightly above the limit, but this is sufficient to invalidate its use as drinking water.Hydrogeotoxic risk or hydrogeotoxicity (HGT) is defined as the quotient between the observed concentration of an element and the limit set by health regulations (such as by the World Health Organization, WHO). Areas at risk of HGT from a given Potentially Toxic Geogenic Trace Element (PTGTE) are defined a quotient of >1.Hydrogeotoxicity of arsenic and uranium (HGTAs and HGTU) were calculated for water samples and 34% returned HGTAs above 1. For uranium, different HGT indexes were considered against a variety of thresholds for drinking water established by different countries and organizations (10μg/L, Germany; 15μg/L, WHO, 2004; 30μg/L, WHO, 2011/US-EPA, 2011): 48% samples returned HGTU10>1; 29% samples, HGTU15>1 and 7% had HGTU30>1. In the water samples analyzed, the highest arsenic content were usually associated with the highest uranium concentrations. However sometimes these two hydrogeotoxicities do not coincide and the HGTAs and HGTU10 distributions show different patterns.Hydrogeotoxicity due to more than one element (HGTAs and HGTU10) was also considered; 17% samples showed a potentially hydrogeotoxic risk linked to both PTGTEs, leading to the delimitation of these zones as especially vulnerable to a combined hydrogeotoxic hazard.The linear distribution of HGTAs seems to be related to the structure of the Cenozoic Duero Basin and to deep water inflows that are enriched in As and U, which are associated with its fissured basement. The HGTU can be partly linked to these deep flows with a significant hydrothermal component, but they are also linked to secondary processes occurring in the sedimentary basin, which could explain the scattered distribution of HGTU in some areas.As well as the HGT values, which are based on total concentrations, bioavailability of arsenic and uranium species was also considered in order to provide a comprehensive assessment of hydrogeotoxic risk over the study area. In all samples with HGTAs>1, arsenic was present as As(V) inorganic form. Likewise, in samples with HGTU10>1, uranium appears as U(VI). This hydrogeotoxic anomaly must be related to both the chemical and radiological hazards.

Hydrochemistry and 222Rn Concentrations in Spring Waters in the Arid Zone El Granero, Chihuahua, Mexico

Water in arid and semi-arid environments is characterized by the presentation of complex interactions, where dissolved chemical species in high concentrations have negative effects on the water quality. Radon is present in areas with a high uranium and radium content, and it is the main contributor of the annual effective dose received by humans. The objective of this study was to evaluate concentrations of 222Rn and the water quality of spring waters. Water was classified as calcium sulfated and sodium sulfated. Most of the water samples with high radon concentrations presented higher concentrations of sulfates, fluorides, and total dissolved solids. 222Rn concentrations may be attributed to possible enhancement of 226Ra due to temperature and salinity of water, as well as evaporation rate. In 100% of the sampled spring waters the 222Rn levels exceeded the maximum acceptable limit which is proposed by international institutions. Aridity increases radiological risk related to 222Rn dose because spring waters are the main supply source for local populations. The implementation of environmental education, strategies, and technologies to remove the contaminants from the water are essential in order to reduce the health risk for local inhabitants.

High Uranium Concentrations in Groundwater in Burundi

Uranium occurs naturally in groundwater and frequently exceeds maximum admissible concentration levels. Here we present the results of a study from Burundi where dissolved uranium concentrations can exceed 700 μg/L. A conceptual model is proposed that relates these high levels to strong evapotranspiration of groundwater where uranium appears by dissolution of minerals from the granitic host rock. The proposed model is consistent with water balance considerations and corroborated by simulations using the geochemical code PHREEQC. Varying degrees of evapotranspiration, mineral dissolution and uranium concentrations of the source rock account for the large variation of the chemical composition of groundwater observed in the study area. These findings highlight the need for caution when developing water supply systems in the vicinity of groundwater discharge zones characterized by strong evapo-concentration.

An evaluation of paired δ18O and (234U/238U)0 in opal as a tool for paleoclimate reconstruction in semi-arid environments

Authigenic opal deposits are widespread in semi-arid and arid environments and often contain high uranium concentrations that facilitate high-precision dating by U-series and U-Pb geochronology. However, despite their ubiquity and utility for placing temporal constraints on surficial processes, the potential for authigenic opal deposits to be used as archives of past climate variability remains largely unexplored compared with more frequently used authigenic carbonate deposits. Here we investigate the potential for authigenic opal deposits to provide records of paleoclimate and paleohydrologic variability through the development of a combined record of uranium ((234U/238U)0) and oxygen (δ18O) isotope variability using in situ ion microprobe methods on opal deposits from Pinnacles National Park, California that precipitated from approximately 16 to 3ka. Pinnacles opal (234U/238U)0 suggests a moderate decrease in net infiltration from the early to middle Holocene, coincident with the timing of increasing aridity inferred from Sierra Nevada lake records, while Pinnacles opal δ18O indicates a relative increase in subtropical storms at the same time. A shift to more North Pacific sourced storms commenced after ~5ka coincident with the easing of aridity in Northern California and increased storminess in the Sierra Nevada as indicated by lake sediment records. These results suggest that useful insights about past hydrologic change can be gleaned from authigenic opal deposits, and that these deposits have the potential to enhance the spatial and temporal coverage of paleoclimate reconstructions in regions where other archives might be scarce. However, further study of the influence of water in opal on δ18O variability and additional in situ analysis of δ18O variability on longer-lived opal deposits with uniform growth histories are necessary to verify the controls on this potential proxy. Similarly, further investigation into short-term and spatial variability in (234U/238U)sw will improve qualitative and quantitative applications of (234U/238U)0 in authigenic opal deposits, enhancing our ability to use this promising new paleoclimate archive.

Contribution A La Caracterisation Diagraphique Des Depots Carbonates Du Cretace Du Bassin Sedimentaire De Cote D’ivoire

To know the petrophysical characteristics associated with sedimentary facies gammay ray logs providing information on the natural radioactivity of sedimentary rocks and the sonic logs which document on facies and petrophysical variations rocks were studied. This study focused on three (3) wells (BH-X, DH-X and MR-X) bored in the offshore basin of Abidjan margin (Côte d’Ivoire) for which the lithogy is constituted of clay alternating with sand an sandstone at the base surmounted by limestone and marls which are covered by clay series. It reveals that two deposits phases occurred during the carbonate sedimentation. Through the gamma ray logs, it appears that the clay phases have low radioactivity, which often progress to average values. This radioactivity recorded in clays would be linked to the low organic matter content and leaching reworked elements. In marl phases radioactivity is medium to high indicating a high content of uranium, thorium and potassium deriving from clay minerals. The gamma ray log varies significantly in limestone phases reflecting the heterogeneity of deposits. Strong radioactivity values in some limestone layers are related to their homogeneity and the present of organic matter. Fluctuations result from long-term changes in submarine hydrothermal flow and may indicate significant variations in facies (crystalline limestone, marl and clay). There are more or less dolomitised layers alternating with more homogeneous chemical limestone benches, biogenic limestone debris of organisms and past clay. The sonic log has two phases in the marl and limestone interval. In the marl phase, the acoustic wave velocity is almost constant, but in the limestone phase velocities fluctuate. Indeed, marl interval contains heterogeneous deposits. Generally the velocity is still low in impermeable and little porous clay. In marls, relatively high propagation velocity implies that they are less penetrable as clays because of the presence of fluid. The sonic log fluctuations in the limestone stage reflect the heterogeneity of deposits. Calcareous layers generally have a shorter time of wave propagation, suggesting that they are indurated, recrystallized and homogeneous. By against certain layers are poorly penetrable and show the presence of fluid. The limestone is fractured, so more porous than clay and marl. The porosity may be related to diagenesis after being dessoluted.

Correction methods for uranium analysis by DNAA

Uranium determination by delayed neutron activation analysis is carried out by comparing the delayed neutron counts of a test sample to those of a uranium standard irradiated under identical conditions. Inaccurate results are obtained at high uranium concentrations (greater than approximately 0.05 mg 235U), due to the deterioration of the linear relationship between delayed neutron counts and uranium content, and also when the sample matrix contains other elements that are neutron enhancers or absorbers, for example rare earth elements. In this paper, a correction method has been developed for the accurate analysis of samples with high uranium content (e.g. uranium peroxide). A second correction method, based on the thermal neutron self-shielding calculation developed by Chilian et al., has been applied to DNAA for the first time to correct for neutron absorption interferences in uranium analysis of rare earth-containing samples.