ahmed tawfic - Academia.edu (original) (raw)

Papers by ahmed tawfic

Research paper thumbnail of Validation of the Optimized Parameters for Improvement of Gamma Spectrometers Performance and Efficacy

Physics of Particles and Nuclei Letters, 2021

This work investigates in some details the conditions and parameters affecting and controlling th... more This work investigates in some details the conditions and parameters affecting and controlling the performance of three different types of HpGe spectrometers. The quality and accuracy of any results depend on the optimum working parameters. The major geometrical and electronics parameters were comprehensively studied and validated for n- and p-type germanium detectors. The spectrometers, at the optimized conditions, were then used for analysis of IAEA reference materials as quality control measure. The Angel-3 software was also used with standard point sources for generation of efficiency curves. The results of the optimized parameters verification for enhancing the systems performance, the minimum detectable activity (MDA), the figure of merit (FOM) and specific activity (SA) assessment were precisely validated, calculated and discussed with equations, figures and tables presentations.

Research paper thumbnail of Investigation of Natural Radioactivity in Wadi El Reddah Stream Sediments and Its Radiological Implications

Radiochemistry, 2021

Abstract Wadi El Reddah has radiation exposure due to the presence of different types of complexe... more Abstract Wadi El Reddah has radiation exposure due to the presence of different types of complexed rocks along with a huge sector of Hammamat sedimentary rocks, monzongranites of Gabal El Reddah, perthitic leucogranites of Gabal Gattar, as well as swarms of post-granitic dykes. The studied sediments show wide variation in their uranium, thorium, radium (eU), and potassium (K, %) contents. The U content ranges from 5 to 51 ppm with an average of 17.33 ppm; the Th content, from 16 to 141 pp with an average of 32.47 ppm. Ra (eU) varies from 5 to 26 ppm with an average of 9.56 ppm, and the potassium content ranges from 2.19 to 4.41% with an average of 3.19%. The absorbed dose rate ( D ), annual effective dose equivalent (AEDE), radium equivalent activity (Ra eq ), external ( H ex ) and internal ( H in ) hazard indices, and the activity gamma index ( I γ ) caused by gamma-emitting natural radionuclides were determined from the obtained values of the 238 U, 232 Th, and 40 K content. Most of the studied samples were out of range with respect to the universal standards.

Research paper thumbnail of Mineralogical and natural radioactivity investigations of Wadi El Reddah stream sediments

International Journal of Environmental Analytical Chemistry, 2020

Wadi El Reddah (valley), Central Eastern Desert, Egypt extends in North-South direction, it repre... more Wadi El Reddah (valley), Central Eastern Desert, Egypt extends in North-South direction, it represents a semi-closed basin with only one outlet in its northern tip. Wadi El Reddah is mainly surrounded by scattered exposures in a sequence of metagabbro-diorite and metavolcanics complex in addition to wide sector of Hammamat sedimentary rocks, monzongranites of Gabal El Reddah, perthitic leucogranites of Gabal Gattar as well as swarms of post-granitic dykes. The studied sediments showed wide variation in their Uranium, Thorium, Radium (eU) and potassium (K%) contents. Uranium ranges from 5 to 51 ppm, with an average of 17.33 ppm, Th contents between 16 and 141 ppm, with 32.47 ppm as an average. Ra (eU) varies between 5 and 26 ppm with an average of 9.56 ppm. While potassium falls between 2.19% and 4.41% with an average of 3.19%. The disequilibrium conditions in the stream sediments under investigation indicated that they are mostly recent which is due to the fact that most of the radiometric measurements are lower than the chemical measurements. eTh/eU ratio values of old uranium deposits in the studied sediments suggested mineralisation in an environment of rapid deposition of rock detritus and poor weathering with the dominance of detrital radioactive minerals like thorite, samarskite, euxenite and xenotime.

Research paper thumbnail of Analysis of natural radionuclides and137Cs using HPGe spectrometer and radiological hazards assessment for Al-Nigella site, Egypt

International Journal of Environmental Analytical Chemistry, 2020

This study aims to evaluate the specific activity levels in soil and shoresediment samples due to... more This study aims to evaluate the specific activity levels in soil and shoresediment samples due to natural radionuclides; 238 U, 232 Th and 40 K, and man-made 137 Cs of Al-Nigella site, Marsa Matrouh government, Egypt. Soil and shore sediment sample selection, preparation, energy and efficiency calibration, Minimum Detectable Activity (MDA) of the HPGe detector was carried out according to the standard approaches. The activity concentrations of the samples ranged from 3.16 ± 0.04 to 36.28 ± 0.83 Bq kg −1 for 238 U series, 0.582 ± 0.01 to 33.35 ± 0.62 Bq kg −1 for 232 Th series and 7.38 ± 0.18 to 477.64 ± 8.12 Bq kg −1 for 40 K and 0.088 ± 0.002 to 3.98 ± 0.09 Bq kg −1 for the artificial 137 Cs. The Radiological contour maps for Al-Nigella were drawn using Surfer_13 software and the hazards index was estimated according to the results of the radioactivity measurements and their levels. All results obtained are within the permissible world average values and compared with the activity concentrations in different countries. The values of the calculated air absorbed gamma dose rate D, Annual effective dose E, Radium equivalent (Ra eq), External hazard index (H ex) and Gamma index (Iγ) are below the average international recommended limits as reported by UNSCEAR 2008.

Research paper thumbnail of Chemical alteration processes for uranium migration and their significance on uranium isotopic ratio changes

International Journal of Environmental Analytical Chemistry, 2019

Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments.... more Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments. Geochemically, silicification, desilicification, sericitisation, fluoritisation and Na-metasomatism are the main alteration features of alkali feldspar granites. The activity concentration of 238 U in alkali feldspar granites ranged between 1.7 ± 0.1 Bq g −1 and 3.9 ± 0.3 Bq g −1 ; between 1.7 ± 0.2 Bq g −1 and 9.4 ± 1.4 Bq g −1 for 234 U and between 0.012 ± 0.0002 Bq g −1 and 0.09 ± 0.0001 Bq g −1 for 235 U. The activity concentration of 228 Th ranges between 1.3 ± 0.1 Bq g −1 and 3.6 ± 0.8 Bq g −1 ; between 1.5 ± 0.2 Bq g −1 and 2.7 ± 0.7 Bq g −1 for 230 Th and between 1.8 ± 0.3 Bq g −1 and 4.1 ± 0.4 Bq g −1 for 232 Th. The variability in Chemical Index of Alteration (CIA) with U, Th, 230 Th/ 238 U and 230 Th/ 234 U for the studied altered granite indicates that U and Th concentrations increased with increasing alteration especially in the silicified and desilicified samples. Changes in U, Th, 230 Th/ 238 U and 230 Th/ 234 U suggest the role of alteration processes in uranium and thorium mobilisation though thorium is geochemically less mobile or immobile. Thorium mobilisation could be controlled by adsorption in the alteration products of Abu Garadi granites such as clay minerals, manganese and iron oxides. In contrast, 230 Th/ 238 U and 230 Th/ 234 U decreased with increasing CIA values suggesting uranium accumulation. 234 U/ 238 U ratios were in equilibrium in most samples; this might suggest the effect of severe chemical weathering or alteration processes that leads to the leachability of the two radionuclides (234 U, 238 U) with the same ratio probably during kaolinisation processes. In contrast, 230 Th/ 238 U and 230 Th/ 234 U>1 were in disequilibrium, suggesting the changes in the physicochemical conditions accompanying the different alteration processes.

Research paper thumbnail of Uranium-series disequilibrium as a tool for tracing uranium accumulation zone in altered granite rocks

International Journal of Environmental Analytical Chemistry, 2019

Abu Garadi area is mainly represented by metasediments, alkali feldspar granites and stream sedim... more Abu Garadi area is mainly represented by metasediments, alkali feldspar granites and stream sediments. The granitic mass described different degrees of hydrothermal alterations like albitization, greisenisation, hematitisation, silicification and koalinitisation which are mostly restricted to the faults. Uranium mineralisation in these granitic rocks is mainly controlled by the sheared granite parts. Various radionuclides from uranium decay series such as (238 U, 234 U, 235 U, 230 Th, 226 Ra) and 40 K in the altered granite of Abu Garadi area that located in central Eastern Desert, Egypt are used to localise uranium accumulation sites in this pluton. Uranium and Thorium contents indicate that these altered granites have high thorium and high uranium granites. Th/U ratios vary between 0.81 and 5.79 with an average of 2.64, which suggests the presence of these samples in the transitional oxidation-reduction zone as evidenced by Th/U ratios>2 and reduction zone as suggested by Th/U ratios<2, respectively. 238 U/ 235 U, 234 U/ 235 U, 234 U/ 238 U, 230 Th/ 238 U, and 226 Ra/ 230 Th activity ratios confirm that most samples of Abu Garadi altered granite lie in the U-accumulations zone. All investigated samples clarify that uranium-series disequilibrium is a technique to trace the recent migration of uranium in these altered granites by the characterisation of the oxidation-reduction boundary.

Research paper thumbnail of Validation of the Optimized Parameters for Improvement of Gamma Spectrometers Performance and Efficacy

Physics of Particles and Nuclei Letters, 2021

This work investigates in some details the conditions and parameters affecting and controlling th... more This work investigates in some details the conditions and parameters affecting and controlling the performance of three different types of HpGe spectrometers. The quality and accuracy of any results depend on the optimum working parameters. The major geometrical and electronics parameters were comprehensively studied and validated for n- and p-type germanium detectors. The spectrometers, at the optimized conditions, were then used for analysis of IAEA reference materials as quality control measure. The Angel-3 software was also used with standard point sources for generation of efficiency curves. The results of the optimized parameters verification for enhancing the systems performance, the minimum detectable activity (MDA), the figure of merit (FOM) and specific activity (SA) assessment were precisely validated, calculated and discussed with equations, figures and tables presentations.

Research paper thumbnail of Investigation of Natural Radioactivity in Wadi El Reddah Stream Sediments and Its Radiological Implications

Radiochemistry, 2021

Abstract Wadi El Reddah has radiation exposure due to the presence of different types of complexe... more Abstract Wadi El Reddah has radiation exposure due to the presence of different types of complexed rocks along with a huge sector of Hammamat sedimentary rocks, monzongranites of Gabal El Reddah, perthitic leucogranites of Gabal Gattar, as well as swarms of post-granitic dykes. The studied sediments show wide variation in their uranium, thorium, radium (eU), and potassium (K, %) contents. The U content ranges from 5 to 51 ppm with an average of 17.33 ppm; the Th content, from 16 to 141 pp with an average of 32.47 ppm. Ra (eU) varies from 5 to 26 ppm with an average of 9.56 ppm, and the potassium content ranges from 2.19 to 4.41% with an average of 3.19%. The absorbed dose rate ( D ), annual effective dose equivalent (AEDE), radium equivalent activity (Ra eq ), external ( H ex ) and internal ( H in ) hazard indices, and the activity gamma index ( I γ ) caused by gamma-emitting natural radionuclides were determined from the obtained values of the 238 U, 232 Th, and 40 K content. Most of the studied samples were out of range with respect to the universal standards.

Research paper thumbnail of Mineralogical and natural radioactivity investigations of Wadi El Reddah stream sediments

International Journal of Environmental Analytical Chemistry, 2020

Wadi El Reddah (valley), Central Eastern Desert, Egypt extends in North-South direction, it repre... more Wadi El Reddah (valley), Central Eastern Desert, Egypt extends in North-South direction, it represents a semi-closed basin with only one outlet in its northern tip. Wadi El Reddah is mainly surrounded by scattered exposures in a sequence of metagabbro-diorite and metavolcanics complex in addition to wide sector of Hammamat sedimentary rocks, monzongranites of Gabal El Reddah, perthitic leucogranites of Gabal Gattar as well as swarms of post-granitic dykes. The studied sediments showed wide variation in their Uranium, Thorium, Radium (eU) and potassium (K%) contents. Uranium ranges from 5 to 51 ppm, with an average of 17.33 ppm, Th contents between 16 and 141 ppm, with 32.47 ppm as an average. Ra (eU) varies between 5 and 26 ppm with an average of 9.56 ppm. While potassium falls between 2.19% and 4.41% with an average of 3.19%. The disequilibrium conditions in the stream sediments under investigation indicated that they are mostly recent which is due to the fact that most of the radiometric measurements are lower than the chemical measurements. eTh/eU ratio values of old uranium deposits in the studied sediments suggested mineralisation in an environment of rapid deposition of rock detritus and poor weathering with the dominance of detrital radioactive minerals like thorite, samarskite, euxenite and xenotime.

Research paper thumbnail of Analysis of natural radionuclides and137Cs using HPGe spectrometer and radiological hazards assessment for Al-Nigella site, Egypt

International Journal of Environmental Analytical Chemistry, 2020

This study aims to evaluate the specific activity levels in soil and shoresediment samples due to... more This study aims to evaluate the specific activity levels in soil and shoresediment samples due to natural radionuclides; 238 U, 232 Th and 40 K, and man-made 137 Cs of Al-Nigella site, Marsa Matrouh government, Egypt. Soil and shore sediment sample selection, preparation, energy and efficiency calibration, Minimum Detectable Activity (MDA) of the HPGe detector was carried out according to the standard approaches. The activity concentrations of the samples ranged from 3.16 ± 0.04 to 36.28 ± 0.83 Bq kg −1 for 238 U series, 0.582 ± 0.01 to 33.35 ± 0.62 Bq kg −1 for 232 Th series and 7.38 ± 0.18 to 477.64 ± 8.12 Bq kg −1 for 40 K and 0.088 ± 0.002 to 3.98 ± 0.09 Bq kg −1 for the artificial 137 Cs. The Radiological contour maps for Al-Nigella were drawn using Surfer_13 software and the hazards index was estimated according to the results of the radioactivity measurements and their levels. All results obtained are within the permissible world average values and compared with the activity concentrations in different countries. The values of the calculated air absorbed gamma dose rate D, Annual effective dose E, Radium equivalent (Ra eq), External hazard index (H ex) and Gamma index (Iγ) are below the average international recommended limits as reported by UNSCEAR 2008.

Research paper thumbnail of Chemical alteration processes for uranium migration and their significance on uranium isotopic ratio changes

International Journal of Environmental Analytical Chemistry, 2019

Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments.... more Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments. Geochemically, silicification, desilicification, sericitisation, fluoritisation and Na-metasomatism are the main alteration features of alkali feldspar granites. The activity concentration of 238 U in alkali feldspar granites ranged between 1.7 ± 0.1 Bq g −1 and 3.9 ± 0.3 Bq g −1 ; between 1.7 ± 0.2 Bq g −1 and 9.4 ± 1.4 Bq g −1 for 234 U and between 0.012 ± 0.0002 Bq g −1 and 0.09 ± 0.0001 Bq g −1 for 235 U. The activity concentration of 228 Th ranges between 1.3 ± 0.1 Bq g −1 and 3.6 ± 0.8 Bq g −1 ; between 1.5 ± 0.2 Bq g −1 and 2.7 ± 0.7 Bq g −1 for 230 Th and between 1.8 ± 0.3 Bq g −1 and 4.1 ± 0.4 Bq g −1 for 232 Th. The variability in Chemical Index of Alteration (CIA) with U, Th, 230 Th/ 238 U and 230 Th/ 234 U for the studied altered granite indicates that U and Th concentrations increased with increasing alteration especially in the silicified and desilicified samples. Changes in U, Th, 230 Th/ 238 U and 230 Th/ 234 U suggest the role of alteration processes in uranium and thorium mobilisation though thorium is geochemically less mobile or immobile. Thorium mobilisation could be controlled by adsorption in the alteration products of Abu Garadi granites such as clay minerals, manganese and iron oxides. In contrast, 230 Th/ 238 U and 230 Th/ 234 U decreased with increasing CIA values suggesting uranium accumulation. 234 U/ 238 U ratios were in equilibrium in most samples; this might suggest the effect of severe chemical weathering or alteration processes that leads to the leachability of the two radionuclides (234 U, 238 U) with the same ratio probably during kaolinisation processes. In contrast, 230 Th/ 238 U and 230 Th/ 234 U>1 were in disequilibrium, suggesting the changes in the physicochemical conditions accompanying the different alteration processes.

Research paper thumbnail of Uranium-series disequilibrium as a tool for tracing uranium accumulation zone in altered granite rocks

International Journal of Environmental Analytical Chemistry, 2019

Abu Garadi area is mainly represented by metasediments, alkali feldspar granites and stream sedim... more Abu Garadi area is mainly represented by metasediments, alkali feldspar granites and stream sediments. The granitic mass described different degrees of hydrothermal alterations like albitization, greisenisation, hematitisation, silicification and koalinitisation which are mostly restricted to the faults. Uranium mineralisation in these granitic rocks is mainly controlled by the sheared granite parts. Various radionuclides from uranium decay series such as (238 U, 234 U, 235 U, 230 Th, 226 Ra) and 40 K in the altered granite of Abu Garadi area that located in central Eastern Desert, Egypt are used to localise uranium accumulation sites in this pluton. Uranium and Thorium contents indicate that these altered granites have high thorium and high uranium granites. Th/U ratios vary between 0.81 and 5.79 with an average of 2.64, which suggests the presence of these samples in the transitional oxidation-reduction zone as evidenced by Th/U ratios>2 and reduction zone as suggested by Th/U ratios<2, respectively. 238 U/ 235 U, 234 U/ 235 U, 234 U/ 238 U, 230 Th/ 238 U, and 226 Ra/ 230 Th activity ratios confirm that most samples of Abu Garadi altered granite lie in the U-accumulations zone. All investigated samples clarify that uranium-series disequilibrium is a technique to trace the recent migration of uranium in these altered granites by the characterisation of the oxidation-reduction boundary.