Results 1 - 10 of 8437
Results 1 - 10 of 8437. Search took: 0.035 seconds
|Sort by: date | relevance|
[en] Highlights: • MCNP6.1-computed dose conversion coefficients validated against ICRP 74 values. • Surrogate responses characterized for mono-energetic and fission neutron sources. • Responses estimate dose directly or can be re-cast as radiation protection factors. - Abstract: Computational and experimental estimates of radiation protection factor (RPF) values are of significant interest to various defense-related organizations. Values of the operational quantity of ambient dose equivalent were computed, using version 6.1 of the Monte Carlo N-Particle® code (MCNP6.1), for 25 photon energies and 53 neutrons energies. Energy-dependent values for absorbed dose at a 10-mm depth in the 30-cm-diameter ICRU tissue-equivalent sphere, , were estimated using the kerma approximation for photon (MCNP F6:p tally) and neutron (MCNP F6:n tally) radiation fields, and then transformed to fluence-to-ambient dose equivalent conversion coefficients, , using appropriate quality factors, Q, and radiation fluences. MCNP6.1-computed values of were compared with tabulated values from ICRP Publication 74. The published conversion coefficients for photon radiation fields were within the error bounds of all MCNP6.1-calculated values. For neutron fields, the computed and published conversion coefficients agreed within calculated error bounds for neutron energies of 100 keV and above, while responses to neutron fields below 100 keV exhibited the same shape and were consistent with the kerma approximation applied in the computational model. The MCNP6.1 models were then modified to simulate the same radiation fields, but conversion coefficients were calculated in the shielded environment of a surrogate vehicle (steel cube)—in keeping with historical and recent studies—and the ratios of shielded and unshielded vehicle response functions were expressed as energy-dependent RPF values. The MCNP6.1-computed neutron RPF values were compared with two prior experimental studies involving a mono-energetic neutron source and a high-yield, short-duration fission neutron spectrum and found to agree within the uncertainty of the experimentally-measured values. Limitations of the computed RPF values are discussed.
[en] Highlights: • Three iron oxides were synthesized and the performance were compared for arsenic uptake. • Radiotracer studies were done for sorption, kinetics and isotherm studies. • Oxidation state of sorbed arsenic species investigated by solvent extraction method. • Applied successfully to real arsenic contaminated ground waters. • An uptake mechanism was proposed based on the observations. - Abstract: A radiotracer technique was employed to study the sorption of As(III) and As(V) on chemically synthesized iron oxides: magnetite (Fe3O4), goethite (α-FeOOH) and hematite (Fe2O3) by batch equilibration mode. Magnetite and goethite were found to be promising sorbents for arsenic removal and applied to real ground water from West Bengal, India. A solvent extraction method using benzene was applied for the investigation of oxidation state of sorbed arsenic. A sorption mechanism was proposed for interaction of As(III)/As(V) with iron oxides.
[en] Highlights: • Thermal neutron capture cross sections and resonance integrals of 96,102,104Ru. • The cross sections are measured with reference to a55Mn monitor. • Neutrons from an Am–Be neutron source kept inside a concrete bunker is used. • 104Ru data is measured from 105Ru and 105Rh gamma emissions. - Abstract: Thermal neutron capture cross sections and resonance integrals of 96Ru, 102Ru and 104Ru are measured with reference to a 55Mn monitor. The experiments are carried out using the neutrons from an Am–Be neutron source kept inside a concrete bunker. The thermal neutron capture cross sections measured are in good agreement with the evaluations as well as with one of the recent measurements. The resonance integral of 102Ru measured in the present study is in good agreement with older measurements.
[en] Highlights: • Metrology of detecting 226Ra and 228Ra in samples from hydrothermal plumes. • Optimisation of parameters to detect low-levels of 228Ra using γ-ray spectrometry. • Detection limits of 1.5 mBq was achieved using 1-week measurement underground. • Radon emanation was only 0.5%. • Radiopurity of all materials involved were investigated. - Abstract: The radium isotopes 226Ra and 228Ra can provide important data on the dynamics of deep-sea hydrothermal plumes that travel the oceans for decades and have great impact on the ocean chemistry. This study focuses on parameters important for obtaining low detection limits for 228Ra using gamma-ray spectrometry. It is present at mBq-levels in samples collected during the US GEOTRACES 2013 cruise to the Southeast Pacific Ocean.
[en] Inverse square correction factors for wide-angle free-air chambers (WAFACs) and free-air chambers (FACs) for cylindrical, conical and square-prism detectors are required for determining the on-axis air kerma from measurements or Monte Carlo calculations made with these different shaped detectors. Values of air kerma measured with these detectors use an effective volume technique related to the inverse square correction factors. This paper presents these factors in a consistent framework and the relationships between them are made clear. Using Monte Carlo simulations, the various corrections and techniques are shown to be accurate within a statistical precision of about 0.04% or better with the exception of the published correction for square prism detectors which is shown to hold only for thin detectors which have an opening angle corresponding to the NIST and NRCC WAFAC primary standards. A more accurate correction for square prism detectors is presented which properly averages rather than where d is the distance away from the source.
[en] Highlights: • Ground gamma-ray spectrometric data revealed that the study area possesses a wide range of radioactivity, oscillating from 37 to 2164 μR/h, 0.1–170 ppm, 0.1–312 ppm, and 0.2%–7.8% for total count (TC), equivalent uranium (eU), equivalent thorium (eTh), and potassium (K), respectively. The highest radioactive responses are mainly associated with pegmatite outcrops. • Pegmatites are the most radioactive rock unit compared to other rocks in the study area. They are mainly found in the form of dykes and lenses, having different lengths and thicknesses. The pegmatite accompanying anomalies are mostly of spot type. • The HLEM survey revealed some significant and well-defined conductive zones. This may reflect that the sources of the conductive bodies are situated at shallow depths and may continue to considerable depths. The highest value of the conductivity thicknesses is associated with the highest eU anomaly. • A favorable agreement was found between the γ-ray spectrometric and HLEM anomalies. This indicates that the surface radiometric mineralization may continue to deeper depths at these locations. • From the results of gamma-ray spectrometry and HLEM surveys, the study area is of considerable significance, in view of the existence of U mineralizations. The study area can be considered as a promising target for more detailed exploration, trenching, and drilling. - Abstract: Ground gamma-ray spectrometric (GRS) and horizontal-loop electromagnetic (HLEM) surveys were carried out to determine the radioactive anomalous zones and to follow their lateral and vertical extensions in east Gabal (G.) El-Urf area, Northern Eastern Desert, Egypt. This area and its surroundings are mainly covered by basement rocks of Late Precambrian age, represented by quartz diorites and granite porphyry, which are intruded by pegmatites, quartz veins, and basic dykes. These rocks are traversed by dry wadis (dry valleys), which are filled by Quaternary sediments. The ground gamma-ray spectrometric data revealed that the study area possesses a wide range of radioelement concentrations, oscillating from 37 to 2164 μR/h, 0.9–170 ppm, 0.1–312 ppm, and 0.2%–7.8% for total count (TC), equivalent uranium (eU), equivalent thorium (eTh), and potassium (K), respectively. The eU composite image showed that high radioactive parts are mainly associated with the pegmatite rocks. Ground HLEM survey was performed at four frequencies (7040 Hz, 1760 Hz, 440 Hz, and 110 Hz) in the study area. The interpretation of the HLEM data indicated the presence of various conductive zones, mainly associated with pegmatite bodies. The parameters of source causative bodies, such as location, dip angle, width, and conductivity thickness were estimated for three conductive bodies. The calculated depths to the selected HLEM anomalies appear to be shallow, varying from 10 m to 22 m. All the anomalous bodies have dips ranging between 60° and 80° toward the south and west. The widths of the anomalous bodies range from medium conductors (13 m) to broad conductors (40 m or more). The conductivity thicknesses showed a wide range (1.14–72.7 Siemens), with the highest value associated with the highest eU anomaly.
[en] Highlights: • Stable isotopes of water show that surface waters are impacted by evaporation due to the aridity of climate and that recharge area of the aquifer is located in local high elevations. • Water quality is impacted by nitrate contamination. • δ15N values, used for the first time in this area, indicate that the main sources of nitrate are septic and manure. • Results indicate rock-water interaction, sea-water intrusion and anthropogenic influence. - Abstract: The Massa basin in Morocco suffers from water scarcity and water quality degradation largely due to salinity and nitrate contamination. In this study, a multi-tracer approach, was used that integrated water chemistry, stable isotopes of water (δ18O, δ2H) and stable isotopes of nitrate (δ15N, δ18O), to investigate mineralization and nitrate contamination in the Massa catchment. The main objective was to identify, for the first time in the area, water pollution sources, with an emphasis on nitrate-originated contamination using the δ15N isotope. Water samples were collected from rivers, dams, wells, boreholes and springs, from different parts of the area (irrigated farms, along Massa River, Anti-Atlas Mountains and coastal areas). The results show a large variability of water mineralization in space indicating rock-water interaction, sea-water intrusion and anthropogenic influence. The lowest mineralization value is measured in spring water located in the Anti-Atlas Mountains while the highest one is measured in Massa River. The results also show a large variability of NO3 with high contents in many sites. Some domestic wells showed the highest NO3 concentrations. The field investigation reveals a practise where domestic wastewater is being poured directly into traditional septic tanks. 15N results indicate mixing origins of nitrate related to sea-water intrusion, NH4 fertilizers and manure septic which constitute the main issue. Our results will be an essential recommendation for decision-makers for the implementation of wastewater treatment systems before they are discharged into the environment. Improving individual septic systems is also a necessary condition.
[en] Highlights: • A method for enhancement of the Neutron Computerized Tomography image is presented. • The effect of the projection exposure time on the quality of NCT image is studied. • The sample was exposure at the ETRR-2 Reactor at power operation (17 MWth). • The results show, high-quality image obtained. • The results show, the projection exposure time equal to 4 seconds gives the best quality image. - Abstract: This paper presents a proposed procedure for neutron radiography image enhancement through studying the effect of the projection exposure time on the quality of Neutron Computerized Tomography (NCT) image. A sample was exposure at the Egyptian Second Research Reactor (ETRR-2) NCT facility with projection exposure time varying from one second to six seconds at reactor power operation of 17 MWth. The NCT image was corrected against the read-out noise using flat and dark current images. Then, the Region of Interest (ROI) is selected based on an automatic threshold of the occurrence histogram of the image variance. After that, the image was normalized and filtered by median filter. The resultant images were evaluated qualitatively and compared with the images obtained from Octopus 8.5 software that is currently used in the Egyptian NCT facility. The results indicated that high-quality images had accomplished in comparison with Octopus 8.5 software without losing any information. In addition, with respect to quality measures, the image at the projection exposure time equal to 4 seconds is the best obtained image.
[en] Highlights: • RTD measurements were carried out in a ball mill using radiotracer technique. • Mean residence times were determined in the mill and the separator were determined. • High degree of axial mixing was found in mill. • No mixing was found to occur in the separator. - Abstract: A radiotracer investigation was carried out in a ball mill of a cement plant in Kenya. Residence time distribution (RTD) of raw feed to the mill was measured using Technetium-99m adsorbed on the clinkers as a radiotracer. From the measured RTDs, solid holdup and mean residence times (MRTs) in the ball mill and associated separator were determined. The measured RTDs were modelled using axial dispersion model (ADM) and tank-in-series model both connected with a plug flow component in series. The results of the modelling indicated significant degree of backmixing within the ball mill and no axial mixing in the separator.
[en] Highlights: • A methylthymol blue–polyvinyl alcohol–glutaraldehyde dosimeter has been studied by nuclear magnetic resonance analysis. • The MTB-PVA-GTA dosimeter has a reproducible linear dose response up to 40 Gy. • No significant dose rate and photon energy effects were observed. - Abstract: A new formulation of hydrogel dosimeter consisting of ferrous–methylthymol blue (MTB)–polyvinyl alcohol (PVA) cross-linked chemically with glutaraldehyde (GTA) was studied and evaluated by nuclear magnetic resonance analysis by means of the R2 spin-spin relaxation rate. Previous optical studies of this transparent solid chemically cross-linked gel showed important dosimetric features in terms of sensitivity, auto-oxidation rate, and diffusion. This study shows that the MTB-PVA-GTA dosimeter has a reproducible linear dose response up to 40 Gy. For the optimum formulation of 0.1 mM MTB, 2.5% PVA, and 26.6 mM GTA, the measured R2 sensitivity was higher than that of traditional natural matrix–containing gels (MTB-gelatin) and all other reported PVA gel–based radiochromic dosimeters with MTB, xylenol orange (XO), or GTA (MTB-PVA, XO-PVA, XO-PVA-GTA). Additionally, the auto-oxidation rate was approximately ten times lower than that of the Fricke-MTB-gelatin system, which is consistent with the spectrophotometry results. The results of the independent experimental spectrophotometry and nuclear magnetic resonance analyses indicate that the transparent cross-linked dosimeter has good and consistent dosimetric features.