High Uranium Content Research Articles

Metrological system for?-ray spectrometry measurement of the specific activity and mass fraction of natural radioactive elements in soil and rock samples

In the last few years a great deal of attention has been devoted to the study of the radiation conditions, which in some regions change markedly as a result of intense human activity. One reason for radioactive contamination of an area is dissemination during extraction and processing of radioactive ores or other minerals of natural radioactive elements with a high content of potassium, uranium (radium), and thorium. Estimation of the level of radioactive contamination is one of the main problems of ecological monitoring, and the quality of the measurements sometimes plays a deciding role in the fate of the object being investigated. This also pertains to, in particular, estimation of radioactive contamination of minerals employed for building homes and factories and other industrial structures. In order to draw unequivocal and well-founded conclusions from measurements of the content of natural radioactive elements in soil and rock samples, collected at the object being investigated, a great deal of attention must be devoted during the organization of the measurements to the metrological system.

Multiple Reaction Fronts in the Oxidation-Reduction of Iron-Rich Uranium Ores

This paper describes the oxidation of iron-rich uranium-bearing rocks by infiltration of ground-water. A reaction-diffusion model is set up to describe the sequence of reactions involving iron oxidation, uranium oxidation and reduction, sulphuric acid production, and dissolution of the host rock that occur. On a geological timescale of millions of years, the reactions occur very fast in very thin reaction fronts. It is shown that the redox front that separates oxidized (orange) rock from reduced (black) rock must actually consist of two separate fronts that move together, at which the two separate processes of uranium oxidation and iron reduction occur, respectively. Between these fronts, a high concentration of uranium is predicted. The mechanics of this process are not specific to uranium-mediated redox reactions, but apply generally and may be used to explain the formation of concentrated ore deposits in extended veins. On the long timescales of relevance, a quasi-static response results, and the probl...

The distribution of radioelements in El Gluf biotite granite, north Eastern Desert, Egypt: a guide to the recognition of anomalously radioactive zones

El-Gluf area is located in the north Eastern Desert of Egypt. It is underlain mainly by Precambrian basement rocks and Phanerozoic sediments. It has been systematically surveyed using high-sensitivity airborne gamma-ray spectrometric and magnetic methods. To identify and outline significant radiometric zones of anomalously high uranium and thorium concentrations in El Gluf biotite granite. These zones could be favourable for potential economic radioactive and/or metallic mineralization. This study could serve as a model for investigating the relationship between the geological structure and radioactive mineralization. Statistical analysis of the gamma-ray spectrometric data were carried out to delineate anomalies. A two-dimensional trend analysis of faults as tracedfrom the geological map, the radiometric gradients, magnetic lineations and the courses of wadis (valleys) were carried out to delineate major and minor trends in the area. Seven spectrometric anomalies (two pure uranium, two pure thorium, and three mixed) could be related to the prevailing faulting directions: N-S, N-W and NE. The NW and NE fault trends proved to have a significant impact on the localization of radiometric anomalies, which may point to potential and structurally controlled uranium and thorium mineralizations whose structures are considered to have acted as channel ways for the mineralized solutions.

Spectrophotometric method for the determination of vanadium in uranium rich hydrogeochemical samples using pyridyl azo resorcinol (PAR)

A simple and precise method has been developed for the determination of traces of vanadium(V), using 4-(2 pyridyl azo) resorcinol, in natural water samples, containing very high concentrations of uranium. CDTA—pyrophosphate buffer has been used for masking interferants, including uranium which otherwise interferes above 125 ppb. The reaction of vanadium with PAR in the presence of buffer requires a waiting period of 45 min. The Sandell sensitivity of the method is 0.003 μg/ml, at 545 nm at an optimum pH of 6.5 ± 0.2. The precision of the method is ± 15% at the 100 ppb level of vanadium(V). The method has been successfully applied to a number of natural water samples during hydrogeochemical exploration.

Effects of radiation damage on infra-red and thermoluminescence properties of natural apatites

Thermoluminescence (TL) and infra-red (IR) spectra from various natural crystals of apatite have been examined. All naturally damaged samples (the amount of damaged being monitored by their fossil fission track density) were found to exhibit a reduced contribution in the thermoluminescence glow intensity relative to that of undamaged one. Annealing the samples for 1 hour at temperature above 500°C resulted in an increase in TL sensitivity. The investigation shows strong evidence that radiation damage is responsible for the reduced TL sensitivity. High uranium content in apatite sample shows an increasing IR peak intensity at 740 cm-1 with increasing annealing temperature.

Significance of the Effect of Mineral Alteration on Nuclide Migration

ABSTRACTIn order to clarify the effect of mineral alteration on nuclide migration, we examined the processes, mechanisms, and kinetics of chlorite weathering, and the uranium concentrations in minerals and rocks at Koongarra, Australia. The observed concentrations of uranium in rocks were compared to those calculated. The sequence of chlorite weathering may be simply expressed as a chlorite → vermiculite → kaolinite conversion. These minerals occur as a function of depth, which corresponds well to uranium concentrations on the meter scale. Iron minerals, closely related to the uranium redistribution, are released during the weathering. The first-order kinetic model of the weathering process suggests that the weathering rate is not constant but time-dependent. The uranium concentrations are qualitatively proportional to the extent of the weathering; the weathered part having higher uranium concentration. Uranium mainly occurs with iron minerals, and sub micron sized saléeite, a uranyl phosphate, is one of the most probable uranyl phases associated with the iron minerals. The uranium fixation mechanisms are probably saléeite microcrystal coprecipitation and sorption to the iron minerals. Our model, which describes uranium concentrations in rocks as a function of time, shows that the transition zone (a vermiculite dominant area) plays an important role in the uranium migration. We have established that weathering of chlorite has affected the redistribution of uranium for more than one million years. The present study demonstrates the significance of mineral alteration when we estimate nuclide migration for geologic time.

Radiological aspects of former mining activities in the Saxon Erzgebirge, Germany

In the Middle Ages, rich silver occurrences were exploited intensively in the Saxon Erzgebirge. The unprofitable ores, the socalled “pechblende”, were dumped as waste materials in the environment. The high uranium and radium contents of these rocks prompted later investigations by Henri Bequerel and Marie Curie. In the city of Schneeberg, most of the houses were built directly on these waste materials. Furthermore, the whole subsoil is crossed by a system of numerous pits and adits; therefore, radon gas from the soil can easily penetrate into the houses. The radon exhalation rates from the soil and also from ground floors in this region increase to values of about 1 Bq/m 2.s. In some houses in Schneeberg, 222Rn concentrations of about 50 kBq/m 3 were found in the living rooms. Maximum values in the cellars were about 200 kBq/m 3. From the inhalation of its short-lived radon daughters, an effective dose of about 1.2 Sv/y may result. Mitigation methods like insulation and subsoil ventilation are proposed, and the efficiency of the different measures are discussed.

Early uses of radionuclides in Mexico

Mexico is traditionally a mining country and the first information about the presence of uranium is related to mine exploitation. Around 1945, when uranium became economically important, a rumor spread that large amounts of Oaxaca's black ceramics were being purchased and sent abroad because of their assumed high uranium content. It was not until 1949 that minerals containing thorium and uranium were declared by law as “national reserves”. In the 40's, a radium emanation plant was installed at the “Hospital General” in Mexico City with the main purpose of carrying out radon seed implantation in tumors. In the 50's, a radium dial-painting facility was operating in the city of Toluca. In 1955, the National Commission of Nuclear Energy (CNEN) was founded by a government decree with two main activities: a training program on “Radiosotope Techniques and Nuclear Instrumentation” and the creation of specialized laboratories. In this paper, a general description of these events and undertakings spanning the decades from 1940 to 1970 is given.

Mitigation Methods in High Radon Areas in Germany

A high radon content in soil is the main cause for high indoor radon concentrations in dwellings. The areas around Ellweiler/Hunsruck, Neuenburg/Oberpflaz and Schneeberg/Erzgebirge are known for their high uranium and radium concentrations in soil. An additional region is classified as a 'high radon area' although there are no known uranium anomalies. This region is situated in the Eifel near the Nurburgring in a terrain of volcanic origin. In the Eifel indoor radon values up to 1500 Bq.m-3 have been detected. The indoor values in Ellweiler and around Neuenburg range from several hundreds up to 8000 Bq.m-3, whereas in Schneeberg, radon concentrations up to 300,000 Bq.m-3 in cellars and 100,000 Bq.m-3 in living rooms have been found in some houses. A general mitigation method of equal efficiency for all high radon-exposed houses does not exist. The radon concentration in a recently built house has been reduced successfully to a tenth by a complete insulation of the walls and the floor of the cellar rooms. By removing the subsoil air below the insulated concrete plate of the cellar, the radon concentration has been diminished to 20% and additional air ventilation has halved the radon values again.

Mitigation Methods in High Radon Areas in Germany

A high radon content in soil is the main cause for high indoor radon concentrations in dwellings. The areas around Ellweiler/Hunsruck, Neuenburg/Oberpflaz and Schneeberg/Erzgebirge are known for their high uranium and radium concentrations in soil. An additional region is classified as a 'high radon area' although there are no known uranium anomalies. This region is situated in the Eifel near the Nurburgring in a terrain of volcanic origin. In the Eifel indoor radon values up to 1500 Bq.m-3 have been detected. The indoor values in Ellweiler and around Neuenburg range from several hundreds up to 8000 Bq.m-3, whereas in Schneeberg, radon concentrations up to 300,000 Bq.m-3 in cellars and 100,000 Bq.m-3 in living rooms have been found in some houses. A general mitigation method of equal efficiency for all high radon-exposed houses does not exist. The radon concentration in a recently built house has been reduced successfully to a tenth by a complete insulation of the walls and the floor of the cellar rooms. By removing the subsoil air below the insulated concrete plate of the cellar, the radon concentration has been diminished to 20% and additional air ventilation has halved the radon values again.

222Rn behavior at the Latera geothermal field (Northern Latium, Italy)

Permanent probes to sample soil gases were placed at the Latera geothermal field, located in the Volsini Mts., Latium, Italy. Due to high uranium concentrations in the area's alkali-potassic volcanics outcropping, quite high222Rn values, ranging from 9,260 up to 753,000 Bq/m3, were found. The highest radon activities match tectonic structures such as fractures and faults, and a deep high structure which constitutes the geothermal reservoir. These high radon values also conform to a major amount of4He and CO2. The latter gases are enriched in the gaseous phase of the geothermal fluids, and their migration is also controlled by structural features. This suggests that the enrichment of222Rn in the soil gases, can be linked to a direct contribution of226Ra, carried by deep-seated fluids from the reservoir itself.

Radium and uranium in phosphate fertilizers and their impact on the radioactivity of waters

The study of radioactivity in the phosphate fertilizers and waters of the Kanovci area was performed in order to determine the influence of the application of phosphate fertilizers on the radioactivity of waters. The activity of 226Ra, 228Ra, 235U and 238U was measured in different types of phosphate fertilizers and waters by means of γ-ray spectrometry. Surface water, water from drainage channels, shallow groundwater and deep groundwater samples were collected from the Kanovci agricultural and well field area in Eastern Slavonia, where phosphate fertilizers have been used for the past 15 years. 137Cs was also measured in water samples. The typical phosphate fertilizer used in the Kanovci area contains 75 Bq kg −1 of 226Ra, 9 Bq kg −1 of 228Ra, 52 Bq kg −1 of 235U and 1120 Bq kg −1 of 238U. The estimated annual deposition of uranium and radium in soils of the agricultural and well field area in Kanovci is: 4.5 Bq m −2 for 226Ra, 0.5 Bq m −2 for 228Ra, 3.1 Bq m −2 for 235U and 67 Bq m −2 for 238U. The greatest concentrations of both uranium isotopes are measured in water from drainage channels with a mean value of 120 Bq m −3 for 238U and 5.5 Bq m −3 for 235U. The concentrations of both radium isotopes generally increase with depth of water as distinct from uranium, whose concentrations in deep groundwater are much lower. The highest concentrations of 137Cs were measured in water from drainage channels; it was not detected in deep groundwater. The 238U/ 226Ra activity ratio (AR) is the highest in water from drainage channels and the Bosut River, while in deep groundwater the ratio is only 1.6. Results indicate that high uranium concentrations in surface water, shallow groundwater and water from drainage channels are caused by phosphate fertilizer application in agriculture on the Kanovci area.

ESR dating of fossil shells in the Middle to Upper Pleistocene strata in Japan

The accuracy of the ESR ages of fossil shells from the Boso Peninsula, Ooiso Hills and the Miyazaki Plain in Japan in the Middle to Upper Pleistocene were examined. The measurement test with a thermoluminescent dosimeter at the sampling point suggests that the dose rate of cosmic rays must be added to the calculated dose rate from chemical analysis. The results show that the ESR ages are in good agreement with the stratigraphically estimated ages. However, according to the chemical analysis of the mollusc shell itself, several shells give an abnormally high concentration of uranium. This may indicate that the shell has absorbed uranium from outside especially in sandy sediments.

Comparison between lead isotopes 234U/ 238U activity ratio and saturation index in hydrogeochemical exploration for concealed uranium deposits

At several sites where uranium mineralization was known — West Morvan test area and Lodève basin (France), and Cigar Lake (Saskatchewan, Canada) — we have applied both isotopic and conventional geochemical methods based on major and trace elements concentrations for the detection of concealed uranium deposits. Isotopic methods comprise: (1) the analysis of lead isotopes in groundwater, in order to find any contribution of radiogenic lead from the supposed surrounding or overlying mineralizations: (2) the measurement of 234U/ 238U activity ratios, variations of which have been proven to be correlated with the presence of uranium accumulatiions. The conventional geochemical methods consist simply in looking for uranium or accompanying elements in groundwaters. A more elaborate method uses the notion of saturation indices of uranium-bearing minerals, thus requiring accurate and complete determinations of major ions and other parameters of groundwaters. The data show that determination of lead isotopes is efficient in many contexts, and gives results that are rather independent of the geochemical characteristics (i.e., reducing or oxidizing) of the waters. The information is global and expresses the presence of uraiium accumulation in the vicinity of the sampling point. No information about grades and distance to the mineralization can be obtained. The anomalous lead can be transported either in solution or on particles, as lead is readily adsorbed on many substrates such as clays or oxides. The analysis of 234/ 238U activity ratios in groundwaters provide information which is more difficult to decipher. In general, oxidized waters encountering uranium accumulations show high uranium concentrations and low 234U/ 238U activity ratios, but groundwaters which are more reducing or close to uraninite saturation will produce either high 234U/ 238U activity ratios if the exchange surface between uranium-bearing phases and groundwater is large enough to promote preferential 234U enrichment in the fluid phase (selective leaching or alpha recoil) or low 234U/ 238U activity ratios if the exchange surface is smaller. High 234U/ 238U are observed above dispersed uranium accumulations, frequently situated in the vicinity of massive uranium deposits. This pattern is observed at all studies sites, where contrasting signatures between massive ore zones and surrounding secondary mineralizations are found. In this case, the 234U/ 238U activity ratio may give information on the succession of the relative ore grades. The use of uranium concentration anomalies has often been questioned, because: (1) non-significant anomalies may appear in oxidizing waters; (2) reduced waters may not be able to record significant U anomalies. The concept of saturation indices of uranium minerals generally allows a more accurate detection of the mineralized areas, but it requires a careful determination of redox potentials, in some cases by in situ measurements, but more generally by calculating the redox potential from dissolved iron, assuming equilibrium with iron oxides. Waters flowing through mineralized areas are generally saturated with respect to uranium minerals, without any clear U concentration peak (this is the case around the Cigar Lake U deposit). If they are not saturated, they are generally strongly oxidized and thus show very high uranium concentrations (this is the case of the Nord-Tréviels part of the Lodève uraniferous basin). If no uranium accumulation is present, saturation indices are generally strongly negative, but in strongly reducing waters, even far from any uranium deposit, one can obtain uraninite saturation. This is the case in Lodève sulphide-bearing waters, or in alkaline geothermal waters from the Pyrénées. If we analyze both U concentration and U saturation index, we can see that waters flowing through mineralized zones have either high U concentrations or are very close to U saturation. One can say that, with little doubt, any water that does not possess one of these two characteristics is of no interest for uranium detection.

Uranium isotopes in surface waters from southern Africa

The 234U/ 238U activity ratio in river water in southern Africa is generally higher than that reported for rivers in other regions of the world. This is interpreted as due to the prevailing environmental conditions: in this warm dry region mechanical weathering predominates over chemical weathering, causing the isotope activity ratio of leached uranium to be, on average, 2.03 ± 0.42 as compared to a ratio of 1.20 for river water in the more humid tropical and temperate regions. The isotopic composition of leachable uranium from river sediment is similar to that in the water. Rivers draining the Witwatersrand gold and uranium mining area clearly show pollution inputs characterised by high uranium content and low activity ratios.

Recoil and Transmutation Effects in the Migration Behaviour of Actinides

Most actinide nuclides decay by {alpha} emission with the formation of kinetically and electronically excited daughters. The behaviour of heavy recoil atoms can be inferred from the observation of rupture of equilibrium in the natural radioactive series, from hot atom chemistry and from computer simulation of collision dynamics. On the basis of these sources of information, a new chemical model is established for {alpha} recoil chemistry. It postulates that the chemical state of the daughter atom is determined by redox reactions with oxygen interstitials at the end of the trajectory of the recoil atom. The model predicts that in minerals with low uranium content, {sup 234}U tends toward a leachable, oxidized form; on the other hand, in an environment with high uranium content, {sup 234}U is less amenable to oxidation, complex formation and leaching. These findings suggest that the disposal of radwaste would be more appropriate in 'reducing' organic solids than in ceramic matter or glassy material. (orig.).

Gamma Activation Analysis of Rare Earth Elements in Uranium Rocks

A method is proposed for the chemical separation of the rare earth elements (REE) in samples with a high uranium content (0.1% to 3%) with the subsequent γ-ray irradiation in the microtron MT-25. For the quantitative determination of REE the relative analysis method was used. The method allows to analyse the massive samples (from 3 to 10 g) and provides rapidity and good sensitivity (from 10−4% for Ce to 10−5% for Eu).

Diffusion of uranium in compacted sodium bentonite

Sorption and diffusion of uranium in sodium bentonite MX-80 were measured in aerobic conditions. The batch method was used for the sorption measurements and the steady state method for the diffusion measurements. Clear sorption was noticed only when high uranium concentrations were used so that the pH of the solution decreased. The diffusivities of uranium were strongly dependent on the compaction of bentonite so that in the highly compacted samples the diffusion was very restricted. Uranium shows both features of ion-exclusion and sorption. Further studies are, however, needed to explain the diffusion mechanisms of uranium.

INAA of Zr, La, Ce and Nd in geological samples in the presence of different uranium concentratios

Rock samples which contain relatively high concentrations of uranium may create problems of interference produced by fission products, when instrumental neutron activation analysis is used. The isotopes95Zr,140La,141Ce, 143Ce and 147Nd, which are commonly used in the neutron activation analysis of the corresponding elements, are also produced as fission products of235U. For each of these radioisotopes, a contribution factor is calculated theoretically and meaured experimentally using geological samples with different uranium contents.

Extraction ratios and behavior of uranium in atmospheric particulates and surface soils.

The purposes of these studies are to estimate the influence of uranium in environment on the inhabitant's health and to develop the environmental radioactivity monitoring techniques. The extraction ratios of uranium in surface soils and atmospheric particulates, and the distribution of uranium in atmospheric particulates have been investigated by instrumental neutron activation analysis and alpha ray spectrometry. The extraction ratios of uranium in surface soils with HNO3 were ranged from 30% to 60%. The extraction ratios of uranium in atmospheric particulates were almost the same as that of HNO3 or HCl-H2O2, 70% to 80%. By the evaluation of the total uranium contents in surface soils and atmospheric particulates, it was possible to correct the determination values of uranium depending upon acid extraction ratios. Higher concentration of uranium in atmospheric particulates at the daytime was observed than those at the night. At the rainy day, both concentrations of dusts and uranium in atmospheric particulates decreased. Activity ratios of 234U/238U in atmospheric particulates were equal to those in surface soils at the daytime, the night and the rainy day. It was estimated that 80% to 93% of uranium in atmospheric particulates collected in Yokohama city in Kanagawa Prefecture were derived from soils.