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At least 865 records · Page 48Linked to original sources
PubMed2006

Distribution of naturally occurring radionuclides (U, Th) in Timahdit black shale (Morocco).

Attention has been focused recently on the use of Moroccan black oil shale as the raw material for production of a new type of adsorbent and its application to U and Th removal from contaminated wastewaters. The purpose of the present work is to provide a better understanding of the composition and structure of this shale and to determine its natural content in uranium and thorium. A black shale collected from Timahdit (Morocco) was analyzed by powder X-ray diffraction and SEM techniques. It was found that calcite, dolomite, quartz and clays constitute the main composition of the inorganic matrix. Pyrite crystals are also present. A selective leaching procedure, followed by radiochemical purification and alpha-counting, was performed to assess the distribution of naturally occurring radionuclides. Leaching results indicate that 238U, 235U, 234U, 232Th, 230Th and 228Th have multiple modes of occurrence in the shale. U is interpreted to have been concentrated under anaerobic conditions. An integrated isotopic approach showed the preferential mobilization of uranium carried by humic acids to carbonate and apatite phases. Th is partitioned between silicate minerals and pyrite.

Aluminum↗
PubMed1992

Case report: arachnoiditis following intracranial 'Thorotrast'.

A patient is reported with a painless, progressive cauda equina lesion due to arachnoiditis, the result of the contrast medium 'Thorotrast' (thorium dioxide) introduced into the brain over 30 years previously. Contrast medium introduced into the lumbar spine can give rise to aseptic adhesive inflammation (arachnoiditis). It rarely gives rise to clinical problems but, when it does so, is usually associated with back pain and only very rarely with progressive neurological deficit.

Abscess↗
PubMed1998

Multiple, unique, and common p53 mutations in a thorotrast recipient with four primary cancers.

Four primary cancers found at autopsy of a patient who received the thorium-based contrast agent Thorotrast 50 years ago and who was healthy up until a few months before his death from liver failure were analyzed for p53 mutations. The data suggest that the chronic alpha-irradiation may be a large causative factor. Multiple mutations were found in all the cancer tissues: two foci of a cholangiocellular carcinoma, a tubular adenocarcinoma of the stomach, a squamous cell carcinoma of the lung, and an adenocarcinoma of Vater's ampulla. The total number of point mutations detected were 13. Moreover, homozygous aberrations were detected in a large area of normal small intestine and noncancer liver tissues suggesting that nontumor cells which harbored p53 abnormalities gained a survival advantage and clonally expanded.

Adenocarcinoma↗
PubMed2001

Natural radioactivity in phosphates, phosphogypsum and natural waters in Morocco.

The contents of natural radionuclides (uranium, actinium and thorium series) were measured in sedimentary phosphate rock samples using high-resolution gamma spectrometry. Data obtained for uranium content (ppm) were compared with the results obtained by a method based on the measurements using solid-state nuclear track detectors (SSNTD) in the same samples. The potential leaching of radionuclides from sedimentary phosphate rock during the industrial production of the phosphoric acid was studied. The process of leaching of the radioisotopes from phosphogypsum was discussed. A method for the direct alpha counting of 226Ra thin source, elaborated by the deposition of Ra from aqueous solutions on manganese oxides film deposited on polyvinyl support, have been developed and applied for the determination of 226Ra in natural water samples. The results show that only the water sample from the mine area reveals the presence of 226Ra at a level of about 0.2 Bq l-1.

Actinium↗
PubMed2002

Distribution and mobilization of U, Th and 226Ra in the plant-soil compartments of a mineralized uranium area in south-west Spain.

The activity concentrations of natural uranium isotopes (238U and 234U), thorium isotopes (232Th, 230Th and 225Th) and 226Ra were studied in soil and vegetation samples from a disused uranium mine located in the Extremadura region in the south-west of Spain. The results allowed us to characterize radiologically the area close to the installation and one affected zone was clearly manifest as being dependent on the direction of the surface water flow from the mine. The activity concentration mean values (Bq/kg) in this zone were: 10,924, 10,900, 10,075 and 5,289 for 238U, 234U, 230Th and 226Ra, respectively, in soil samples and 1,050, 1,060, 768 and 1,141 for the same radionuclides in plant samples. In an unaffected zone, the activity concentration mean values (Bq/kg) were: 184, 190, 234 and 7251 for 235U, 234U, 230Th and 226Ra, respectively, in soil samples and 28. 29, 31 and 80 in plant samples. The activity concentrations obtained for 232Th and 228Th showed that the influence of the mine was only important for the uranium series radionuclides. The relative radionuclide mobilities were determined from the activity ratios. Correlations between radionuclide activity concentrations and stable element concentrations in the soil samples helped to understand the possible distribution paths for the natural radionuclides.

Isotopes↗
PubMed2002

Distribution of long-lived radionuclides of the 238U series in the sediments of a small river in a uranium mineralized region of Spain.

A study is presented on the distribution and mobilization of the natural U isotopes (238U and 234U), 230Th, and 226Ra in the sediments of a small river crossing an uranium mineralized zone where a disused uranium mine is located. Due to the preferential directions for surface run-off waters and to the mine's situation, one sampling point along the river bed was identified as a point of accumulation of radionuclides. The average values of the activity concentrations (Bq/kg) in this sediment sample were 5,025, 5,055, 5,915 and 1,694 for 238U, 234U, 230Th and 226Ra, respectively, while the respective average values of the activity concentrations (Bq/kg) for the sediment sample considered to give the background level were 125, 124, 131 and 370. Isotopic ratios between the descendants of 238U served to clarify some paths of distribution, involving the soils nearest to the sampling points and the location of these points with respect to the disused mine. The differences in behaviour found between the uranium, thorium and radium isotopes were associated to the mobility of these radionuclides in the fluvial system studied. Correlations between the radionuclide activity concentration ratios and stable element concentrations in the sediment samples were also investigated.

Fresh Water↗
PubMed2003

Soil-to-plant transfer factors for natural radionuclides and stable elements in a Mediterranean area.

The transfer factors (TF) for natural uranium isotopes (238U and 234U), thorium isotopes (232Th, 230Th and 228Th), and 226Ra were obtained in plant samples (grass-pasture) growing in granitic and alluvial soils around a disused uranium mine located in the Extremadura region in the south-west of Spain. Affected and non-affected areas of the mine presented large differences in the activity concentrations of radionuclides of the uranium series. We also determined transfer factors for several stable elements (essential and non-essential). A set of statistical tests were applied to validate the data. The results showed that the transfer factors for both the natural radionuclides and the stable elements are independent of the two substrate types involved and also of the two areas considered in the study.

Environmental Monitoring↗
PubMed2004

Assessment of the radiological impacts of historical coal mining operations on the environment of Ny-Alesund, Svalbard.

Mineral extraction activities, such as those conducted by oil, gas and coal industries, are widespread throughout the Arctic region. Waste products of these activities can result in significant contributions to the radioactive burden of the surrounding environment due to increased concentrations of naturally occurring radioactive materials (NORM) to levels that would not normally be found in the environment. Coal mining operations commenced in the early 1900s on Svalbard and have been conducted at a variety of locations on the archipelago since then. Coal contains radionuclides of the uranium and thorium series as well as 40K. Extraction and processing of coal can result in releases of these radionuclides to the broader environment with subsequent impact on the human and non-human inhabitants of the area. This paper presents the results of a study on environmental radioactivity resulting from historical coal mining operations conducted at Ny-Alesund, Spitsbergen, in the Svalbard archipelago. Activity concentrations of radionuclides found in materials associated with these operations are presented as well as the results of a spatial dosimetric survey conducted over an area affected by coal mining.

Arctic Regions↗
PubMed1999

Particle size separation via soil washing to obtain volume reduction.

A pilot-plant study was performed using a soil washing pilot plant originally designed by the Environmental Protection Agency (EPA) to demonstrate scale-up and potential full-scale remediation. This pilot plant named VORCE (Volume Reduction/Chemical Extraction) was modified to meet the specific requirements for treatment of the Formerly Utilized Sites Remedial Action Program (FUSRAP) and a Department of Energy site soils. After a series of tests on clean soils to develop operating parameters and system performance, the machine was used to treat soils, one contaminated with Thorium-232 and the other with Cesium-137. All indicate that soil washing is very promising for volume reduction treatment. In addition, cost data was generated and is given herein.

Cesium Radioisotopes↗
PubMed1975

High resolution imaging properties of the STEM.

The effect of the finite size of the atom on the resolution of the STEM is investigated. When the probe size becomes comparable to the size of the atom, the quality of the image depends on the scattering properties of the atom as well as the distribution of electrons in the probe. A technique for calculating the image of a single atom is developed by expanding the scattering amplitude. This allows the image of an atom or its spatial frequency to be expanded into various components. The specific case of dark field contrast formed with elastically scattered electrons is considered. The coefficients of the components are evaluated for carbon and thorium using complex scattering amplitudes derived from relativistic Hartree-Fock-Slater wavefunctions. The coefficients are evaluated for a 100 keV microscope using an immersion type objective lens whose aperture is limited to 12 mrad by primary spherical aberration and a 100 keV microscope using the same objective lens in conjunction with a corrector lens for spherical aberration. Secondary spherical aberration limits the objective aperture of the corrected microscope to 30 mrad.

Carbon↗
PubMed1977

Asymmetrical dark field detectors in the STEM.

Although the annular dark field detector in the STEM collects a large fraction of the elastically scattered electrons, it does not use all the information carried by these electrons because it ignores the distribution of electrons over its surface. This information can be obtained by dividing the detector into sections. This paper calculates the number of electrons scattered by a single atom onto each side of an annular dark field detector split in half by a line passing through its center. This scattering problem is unusual becuase the incident wave is not a plane wave in the STEM. The sum and difference signals are calculated for a single atom from its scattering amplitude for a STEM limited by primary or secondary spherical aberration operating at 10 kV, 70kV, or 100 kV. All the cases calculated show that a single thorium atom should give an observable difference signal which is very sensitive to the focal conditions of the STEM.

Electrons↗
PubMed2001

The potencial role of rare earths in the pathogenesis of interstitial lung disease: a case report of movie projectionist as investigated by neutron activation analysis.

A 60-year-old male subject who worked as a movie projectionist and who was exposed for 12 years to rare earths (RE) containing dusts from cored arc light carbon electrodes was investigated. Chest X-ray films and pulmonary function tests showed an interstitial lung disease, emphysema and a severe obstructive impairment with marked decrease of carbon monoxide diffusion capacity. The histological examination of a transbronchial biopsy confirmed the diffuse interstitial lung fibrosis. Neutron activation analysis (NAA) of the biopsy showed concentrations of cerium (Ce), lanthanum (La), neodimium (Nd), samarium (Sm), terbium (Tb) and ytterbium (Yb) which were high compared to the corresponding elements in the transbronchial biopsies of 5 unexposed subjects as a control group. Thorium (Th) (which is generally present as an impurity of the RE compounds) was also determined in order to estimate the radiation dose in the lung of the worker. On the basis of the clinical observations, of the analytical results by neutron activation analysis of RE and of the presence of Th in the transbronchial biopsy, as well as of the differential diagnosis, which tended to exclude other occupational or non-occupational lung diseases, a relation between the observed interstitial lung fibrosis and occupational exposure to RE is highly probable.

Biopsy↗
PubMed2001

Disequilibrium of uranium isotopes in some Syrian groundwater.

Uranium concentration in groundwater samples from three areas of Syria was determined using alpha-spectrometry and INAA. It was in the range of 0-6.13 microg/l in the phosphate areas, and lower than 1 ppb in the volcanic areas. The activity ratio of 234U/238U was investigated, and disequilibrium of uranium isotopes was found to occur (234U/238U = 0.52-2.02). The excess of 234U was calculated. This excess can be interpreted by higher mobility of 234U, which more readily forms the soluble (UO2)2+ ion in comparison with 238U, most of which remains in the insoluble 4+ state. This excess increases with increase in uranium concentration. Thorium concentration was measured using INAA, it was found to be in the rang 0-1.15 microg/l.

Dose-Response Relationship, Radiation↗
PubMed2001

Gamma activity and geochemical features of building materials: estimation of gamma dose rate and indoor radon levels in Sicily.

A high-purity germanium detector has been used to measure the abundance of radium (Ra), thorium (Th) and potassium (K) in building materials used in Sicilian dwellings. The measurements were performed to evaluate which material was suitable for the construction of an enclosure, which would have a low background emission. The materials examined in this work showed concentrations of 226Ra, 232Th and 40K dramatically variable depending on the lithologies, particularly in the case of blocks, sands and aggregates commonly used in building materials in Sicily. The results are discussed and a criterion is indicated to reduce the radiation dose to humans. Since radon inlet is a major health problem, all the radiometric data and the geochemical features have been used to determine the radon exhalation, which arises from the disintegration of 226Ra in soils and walls of houses. From our experimental data it can be seen out that one of the geochemical parameters, Total Alkali (TA), may be an appropriate index to select materials of low radiological risk.

Algorithms↗
PubMed2003

Radioactivity levels of salt for natural sediments in the northwestern desert and local markets in Egypt.

Thirteen samples of salt collected from different locations of old sediments in the western desert at El-Harra and Ain Giffara, Sitra lake and local markets in Egypt have been investigated. Natural radionuclide contents have been measured by gamma-ray spectrometry employing a shielded HPGe detector. The activities of 238U, 232Th and 40K have been determined in Bq/kg dry weight. The absorbed dose rate of gamma radiation was estimated to be 1.46-16.13 nGy/h. The thorium-to-uranium concentration ratios were also estimated for the samples.

Desert Climate↗
PubMed1998

Near-surface disposal of concentrated NORM wastes.

Naturally occurring radioactive material (NORM) in concentrated forms arises in nature and in industry where natural radioisotopes become mobile and then accumulate at particular sites. In industry this often occurs in an acidic environment, where precipitates containing radionuclides plate out onto pipe walls, filters, tank linings, etc. As the radionuclides are selectively deposited, they build up and there is a multiplying effect in terms of the radioactivity concentration. Conditions often tend to favour the build-up of radium, particularly when barium is present and can cause the co-precipitation of radium compounds. As radium is highly radiotoxic, the handling and disposal of such material requires careful management. The state of Western Australia currently has the only low level waste repository in Australia, located at Mt Walton East. To date this repository has been used predominantly to dispose of packaged radioactive waste containing artificial radioisotopes, but there is an increasing demand for the repository to accept bulk concentrated NORM wastes from mining and related industries. Already steelwork from a dismantled phosphoric acid plant and other items contaminated with NORM have been disposed of. The Mt Walton East repository is now proposed as the disposal site for 6000 tonnes per annum of gangue residue from the processing of monazite. The residue contains thorium and a small amount of radium. This paper looks at the technical and related considerations of these disposal operations.

Environmental Exposure↗
PubMed1999

Determination of natural radioactivity in building materials used in the Rawalpindi/Islamabad area by gamma-ray spectrometry and instrumental neutron activation analysis.

Samples of sand and manufactured building materials collected from the Rawalpindi/Islamabad area have been analyzed for the primordial natural radionuclides 238U, 232Th and 40K using gamma-ray spectrometry. The uranium and thorium contents have also been determined by instrumental neutron activation analysis (INAA). The specific activities of these radionuclides in the samples are compared with those of the world averages for soil. The comparison shows that, of the nine samples analyzed, only the three brick samples have higher activities than the world averages for soil. The specific activities in these materials, having a radium equivalent activity of less than 370 Bq kg-1, when evaluated for radiological effects show that all materials meet the external gamma-ray dose limitation of 1.5 mSv y-1. The gamma-spectrometric and INAA techniques complemented each other well in this study.

Calibration↗
PubMed1984

Late effects of perivascular injection of Thorotrast in the neck.

Two cases of late sequelae of accidental perivascular injection of Thorotrast (thorium dioxide) during carotid arteriography are presented. The complaints of the patients and the clinical findings are due to topical granulomatous and fibrous reactions with compression of the carotid artery and cranial nerves, and influence upon larynx and trachea. For future decades it will still be necessary to be aware of this possible cause of neck tumours with oto-laryngeal and neurological symptoms.

Carotid Arteries↗