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Trevisi R.,Research Sector | Cardellini F.,ENEA | Leonardi F.,Research Sector | Vargas Trassierra C.,University of Cassino and Southern Lazio | Franci D.,ARPA Lazio
Radiation Protection Dosimetry | Year: 2014

The inhalation of short-lived radon decay products (RDP) yields the greatest contribution to the natural radiation exposure. This paper deals with a study carried out to improve the knowledge of the behaviour of RDPs, their interaction with particulates and the plateout during the time. The tests confirmed that a high aerosol particle concentration increases the probability that an ion sticks to aerosol and remains long in the air, leading to both an increase of F and a decrease of fp, as reported in the literature. The same experimental protocol applied in a small radon chamber showed a strong reduction of the equilibrium factor (an average of -10 %), because in a small environment the plateout phenomenon prevails on the attachment to particulate. © The Author 2014.

Elsaid M.,Research Sector | Aboelkhair H.,Damietta University | Dardier A.,Research Sector | Hermas E.,National Authority for Remote Sensing and Space science NARSS
Arabian Journal of Geosciences | Year: 2013

In this paper, an attempt was tried to study the relation between radiogenic heat production rate (RHPR) that derived from gamma-ray spectrometric data and the kinetic surface temperature KST, which was calculated from the thermal emission and reflection radiometer-thermal infrared (ASTER-TIR) imagery applied on Elmissikat-Eleridiya district. This area is considered one of the most important uranium localities in the Central Eastern Desert of Egypt. The gamma-ray spectrometric data including both airborne data and in situ measurements concurrent with the collection of 20 rock samples were used to determine the rock density. The ground gamma-ray spectrometry has been conducted using GS-256 spectrometer at the same locations of rock samples. The gamma-ray spectrometric data (airborne and ground) beside rock density data were used for calculating RHPR. Alongside, pairs of daytime and nighttime ASTER-TIR images were collected and surface kinetic temperature for both day (daytime kinetic surface temperature (DKST)) and night (nighttime kinetic surface temperature (NKST)) were derived by using reference channel emissivity technique. The study showed a relative higher RHPR within syenogranite (4.2 up to 6 μW/m3) than other rock units. Besides, the KST of syenogranite ranged from 33 to 48 °C in daytime and between 7 and 17 °C at night. Comparing all results, no clear relation between RHPR and KST is evident. This is due to the very weak RHPR that is not sufficient to affect the surface heat temperature, which can be remotely sensed by ASTER satellite TIR data. This factor in addition to other factors such as: structural elements, topography, geographic locations, shading and scattering, rock moisture and density, can strongly affect the surface temperature. In conclusion, these results could be improved in areas of very high radioelement concentrations, especially 235U and through the use of the enhanced spatial resolution of future satellite TIR imaging instruments. © 2013, Saudi Society for Geosciences.

Lithological, chemical, and stable isotope data are used to characterize lacustrine tufas dating back to prelate Miocene and later unknown times, capping different surfaces of a Tertiary carbonate (Sinn el-Kedab) plateau in Dungul region in the currently hyperarid south-western Egypt. These deposits are composed mostly of calcium carbonate, some magnesium carbonate and clastic particles plus minor amounts of organic matter. They have a wide range of (Mg/Ca)moiar ratios, from 0.03 to 0.3. The bulk-tufa carbonate has characteristic isotope compositions: (δ13Cmean = -2.49 ± 0.99%o; δ18Omean = -9.43 ± 1.40%o). The δ13C values are consistent with a small input from C4 vegetation or thinner soils in the recharge area of the tufa-depositing systems. The δ18O values are typical of fresh water carbonates. Covariation between δ13C and δ18 0 values probably is a reflection of climatic conditions such as aridity. The tufas studied are isotopically similar to the underlying diagenetic marine chalks, marls and limestones (δ13 Cmean = -2.06 ± 0.84%o; δ18Omean =-10.06 ±1.39%o). The similarity has been attributed to common meteoric water signatures. This raises large uncertainties in using tufas (Mg/Ca)moiar, δ13C and δ18O records as proxies of paleoclimatic change and suggests that intrinsic compositional differences in material sources within the plateau may mask climatic changes in the records. © 2013 Elsevier GmbH.

This study presents isotope geochemical analyses conducted on water column samples and core sediments collected from the Swan Lake Basin. Water analyses include the dissolved methane (CH4) content and the ratio of carbon-13 to carbon-12 (δ13C) in dissolved inorganic carbon (DIC). The core sediments - sandy muds containing inorganic calcite, organic matter, and opal phases±ostracods - were examined by X-ray diffraction, dated by radiocarbon (14C), analyzed for wt% organic carbon, wt% organic nitrogen, wt% organic matter, wt% calcite, δ13C of bulk-sediment insoluble organic matter (kerogen), 18O:16O ratio (δ18O) and δ13C of bulk and ostracod calcite. Of particular significance is the large enrichment in carbon-13 (δ13C=+4.5 to +20.4‰ V-PDB) in the calcite of these sediments. The 13C-enriched calcite is primarily formed from DIC in the water column of the lake as a result of the following combined processes: (i) the incorporation of 13C enriched residual carbon dioxide (CO2) after partial reduction to CH4 in the sediments and its migration into the water column-DIC pool; (ii) the preferential assimilation of 12C by phytoplankton during photosynthesis; (iii) the removal of 13C-depleted CH4 by ebullition and of organic matter by sedimentation and burial. The 13C enrichment was low between 3624 and 2470yr BP; high between 2470 and 1299yr BP; and moderate since 1299yr BP. Low 13C enrichment was formed under low water-column carbon levels while higher ones were formed under elevated rates of biomass and calcite deposition. These associations seem to imply that biological productivity is the main reason for carbon-13 enrichments. © 2014 Elsevier GmbH.

As part of an investigation of iron species in fossil wood at the New Cairo Petrified Forest, representative samples, collected from the area, were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), and Mössbauer spectroscopy at room temperature. The samples are composed of silica, with ∼1.2 to ∼17 wt.% Fe2O3, 0.21-0.92 wt.% Al2O3, and 0.001-0.71 wt.% MnO. The other oxides - including TiO2, MgO, CaO, Na2O, K2O, and P2O5 - constituted ∼0.24 to ∼1.4 wt.% of the fossil wood. Mössbauer spectra of the samples, fitted using the hyperfine distribution method, showed a major sextet of Fe3+ in goethite (64.75-100%), another sextet of Fe3+ in hematite (27.62-31.94%), and a doublet (2.01-5.72%) that is attributable to octahedral Fe3+ in superparamagnetic phases. The presence of the iron in the trivalent state in all samples is consistent with high oxygen fugacity environments post-fossilization. Equivalent weights of goethite and hematite in these samples calculated using the relative spectral areas determined by Mössbauer spectroscopy and the iron contents by ICP-MS were 0.84-18.52 and 0.13-0.45 wt.%, respectively. Changes in goethite or hematite abundances in the samples had no effects on their hyperfine parameters. The observed changes in Mössbauer spectra of goethite in the samples studied have been attributed to poor crystallinity, rather than element substitutions. This resulted in a reduction of the average magnetic hyperfine field (to ∼27 T) and an increase in the hyperfine field distribution widths. The effects of poor crystallinity were much less pronounced in the hematite spectrum, with the samples having average room-temperature magnetic hyperfine fields of ∼50.2 T, as expected for bulk hematite. Silica substitutions for iron in the fossil wood samples cannot be ruled out, but the effects of such processes on hyperfine field distributions of the iron are unknown.

Hassan K.M.,Research Sector
Mineralogia | Year: 2015

As part of the characterization of the petrified wood of East Cairo at the New Cairo Petrified Forest, representative samples collected from the area were studied by X-ray powder diffraction (XRD) and optical microscopy. The samples, as indicated by XRD analysis, are composed of quartz ± some goethite ± minor moganite ± minor gypsum ± trace calcite. The absence of moganite in some samples has been attributed to the transformation of moganite to quartz or to leaching processes. Under the optical microscope, some of the 10 petrified-wood samples are permineralized with mainly microcrystalline quartz (chalcedony), some with a combination of chalcedony and microgranular quartz, and some with microgranular quartz. The sequence of silicification is likely to have been either opaline precursor to chalcedony and quartz, or directly to chalcedony and quartz. The crystallinity indices (C.I.) of the quartz in the samples studied, measured using a standard X-ray powder diffraction procedure, are consistent with the petrographic findings. The chalcedonic samples have the least C.I. values, and the microgranular quartz samples the highest values. © 2015 by Kamaleldin M. Hassan.

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