Comparative study of the natural radioactivity of some selected rocks from Egypt and Germany

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1 Indian Journal of Pure & Applied Physics Vol. 44, March 2006, pp Comparative study of the natural radioactivity of some selected rocks from Egypt and Germany N K Ahmed, A Abbady, A M El Arabi, R Michel *, A H El-Kamel ** & A G E Abbady Physics Department, Faculty of Science Qena, South Valley University, Egypt *Institute of the Radiation Protection and Radioecology, Hanover University, Germany **Physics Department, Faculty of Science, Assiut University, Egypt Received 14 March 2005; revised 22 November 2005; accepted 4 January 2006 The radioactivity contents of various radionuclides in rocks play an important role in health physics and geo-scientific research. The naturally occurring radionuclides 226 Ra, 232 Th and 40 K are the main sources of radiation in soil and rocks from which traditional building materials are derived. These radionuclides pose exposure risks externally due to their gamma-ray emissions and internally due to radon and its progenies, which emit alpha particles. The activity concentration (Bq/kg) in igneous and metamorphic rock samples from different locations in Egypt and Germany has been analysed. The concentration values of samples for 226 Ra, 232 Th and 40 K were found in the range of 3.9 : 57.4, 3.2 : 53.4 and 202 : 1211 in Egypt and 5.1 : 76, 3.4 : 70 and 10 : 2070, respectively in Germany. Even though these radionuclides are widely distributed, their concentrations depend on the local geological conditions. Keywords: Radioactivity, Igneous, Metamorphic rock IPC Code: H01J65/08 1 Introduction The gamma-ray spectrometry of rocks is of interest to geochemists, exploration geologists, and radiological health physicists 1. A large amount of data regarding the distribution and geochemistry of natural radionuclides, namely 226 Ra, 232 Th and 40 K in crystalline rocks from several different continental and oceanic island sites have been published 2-4. The distribution of these radionuclides has proved to be important as those on estimates of the level of natural background radiation to which humans are exposed 5, on long and short-range supplies of natural radioactive materials as energy sources 6, on the nature of the Earth s interior as partially based on heat flow measurements and the concentrations of radioactive constituents present in meteorites and ultrabasic rocks 7 and on absolute age determinations as based upon the uranium, thorium and actinium disintegration series 8. The concentrations and distributions of natural radionuclides occurring in rocks have been measured and the level of the background radiation arising from them in the geographic areas treated in present study has been assessed. The activity concentrations (Bq/kg) of the natural occurring radionuclides 226 Ra, 232 Th, and E - mail: Abbady1965@yahoo.com 40 K in igneous and metamorphic rock samples from the Eastern Desert in Egypt (Bir El-Sid and Wady El- Gemal areas) and some rock samples from different locations in Germany were measured using a highpurity germanium detector. 2 Experimental Details One hundred samples were collected from two regions. The first is the Bir El-Sid area, which is located in the Pan-African basement of Egypt. The area covers about 96 km 2 of crystalline basement rocks of Egypt, near midway along the Qift-Qusier road and is confined by the following co-ordinates Longitude: and E and Latitude: and N 9. It contains the following types of rocks: Felsite dykes (acidic dykes), Fawakher granitoid pluton, Lamprophyer and Diorite dykes (intermediate dykes), Dolerite dykes (basic dyke), Fawakher ultrabasic mass (Serpentinite), and Bir El-Sid basic flow sheet (Basalt, Metagabbro). The second area is Wady El-Gemal located at the Red sea some 220 km east of Kom Ombo in the Nile Valley. Latitude : N and longitude: E. It contains various types of rocks, acidic dykes, intermediate dykes, basic dykes, Serpentinite, Metagabbro, Mélange. Another set of igneous and metamorphic rock samples was collected from

2 210 INDIAN J PURE & APPL PHYS, VOL 44, MARCH 2006 different regions of Germany besides some selected building materials. The rock samples under investigation were crushed to small pieces, dried and milled to a fine grain size powder. Each sample was then mixed using an electric shaker to obtain homogeneously powdered material. The powdered samples were shaped to the desired weight and yet guaranteed a good representation of the original sample material. The representative powdered rock samples were filled into polyethylene circular discshaped containers of 55 mm diameter and 13 mm height. Each sample was then compressed in its container using manual pressure till the height reached 10 mm. Finally, the container was completely filled with 10 mm of foam and stored for four weeks to allow to reach the secular equilibrium. Samples were measured using a pre-calibrated high resolution gamma ray spectrometer. The spectrometer used on closed-end coaxial high purity germanium detector, close facing window geometry with vertical dipstick ( microns). The spectrometer was calibrated for efficiency and energy using multi-nuclide standard solution 98-QCY48 PTB (Germany). The standard source peaked in the same geometry as that used for measured samples. For calibration, the standard source is placed above the detector in a well defined geometry, and the measurement is started. The dependence of the efficiency on the radiation energy was determined at 0.0 mm sample-detector distance. The absolute efficiency of the HPGe detector was determined using the standard solution 98-QCY48 PTB (Germany). The detector efficiency decreases continuously with energy. The dependence of the efficiency on the volume of the sample was determined by a bottle (250 ml) and a Petri dish (25 ml). The dependence on efficiency/sample-volume was determined. It can be noticed that the detector efficiency decreases with the volume of the sample in the energy-range of interest. To minimize gamma ray background the detector was shielded with layer of lead, iron bricks, cadmium, copper and plexiglas as fundamental shield besides efficient anti-coincidence system. The measurements were carried out by daily efficiency and energy calibrations, repeating each sample measurements. The counting time was about (10 hr) and sometimes the counting time was expanded to obtain energy spectrum of good resolution. The 226 Ra activities (or 238 U activities for samples assumed to be in radioactive equilibrium) were estimated from 214 Pb (242.2, 295.2, kev) and 214 Bi (609.3, kev ). Several 214 Pb and 214 Bi peaks were also monitored. The gamma-ray energies of 212 Pb (238.6 kev), 228 Ac (338.4, 911 kev) and 208 Tl (583.2 kev) were used to measure the activity concentration of 232 Th, while the 40 K activity was determined from the kev emission. The activity concentrations of the natural radionuclides in the measured samples were computed using the following relation 10 : A S (Bq kg -1 ) = C a / ε P r M s (1) where C a is the net gamma counting rate (counts per second), ε the detector efficiency of the specific γ ray, P r the absolute transition probability of gamma decay and M s is the mass of the sample (kg). The contents m in ( ppm) of U, Th and K in the samples are determined from their measured activity values by applying the equation 11 : m (ppm ) = ( A M / N Av ln 2 ) t 1/2 (2) where A is activity in (Bq/g) of the matter or any daughter in radioactive equilibrium, M the molecular weight (g/mol), N Av the Avogadro s number ( ) and t 1/2 is half-life in seconds. 3 Results and Discussion This study was undertaken for the purpose of measuring concentrations and distributions of natural radionuclides occurring in rocks. The level of background radiation in the geographic areas was treated in this study. The activity concentrations (Bq/kg) of the natural occurring radionuclides 238 U, 232 Th, and 40 K in igneous and metamorphic rock samples from Eastern Desert in Egypt (Bir El-Sid and Wadi El-Gemal areas) and some rock samples from different locations in Germany were measured using a high-purity germanium detector. The various rock types in Bir El-Sid area are transected by a number of dykes, most of which oriented in a NE SW direction. Accordingly, it is expected that the different members of the dykes included in the studied area have the following sequence beginning with the oldest: basic dykes (dolerite dykes), intermediate dykes (lamprophyer, diorite dykes) and acidic dykes 9 (felsite dykes). From the obtained results of dykes, it can be seen that the radium-226 activity concentration for felsite is in the range of 18.4 ± 4.1 to 59.9 ± 4.6 Bq/kg with an

3 AHMED et al.: NATURAL RADIOACTIVITY OF SOME SELECTED ROCKS 211 average value of 35.2 ± 4.6 Bq/kg. The activity concentration of thorium-232 varied from 8.2 ± 3.5 to 54.8 ± 5.1 Bq/kg with an average of 28.6 ± 4.4 Bq/kg, while the activity concentration of potassium-40 varied from ± 98 to ± 88.7 Bq/kg with an average value of 884 ± 73.7 Bq/kg. In lamprophyer, the average concentration values of radium-226, thorium-232 and potassium-40 are 37.2 ± 3.9, 38.8 ± 4.8 and 601 ± 40 Bq/kg, respectively. With respect to diorite and dolerite dykes, the activities of radium-226 range from 12.1± 2.5 to 12.7 ± 6.1 and 9.5 ± 2.5 to 16.6 ± 3.6 with mean values of 12.4 ± 3.9 and 14.5 ± 2.7 Bq/kg, respectively, thorium values was in the range of 7 ±2.7 to 9.9 ±2 and 4 ± 2 to 19.2 ±3 with an average vaule of 8 ±3 to 8.9 ±2 while for potassium-40 the mean values are ± 31.4 and ± 15.8 Bq/kg. It can be seen from the results that the highest values of 226 Ra and 232 Th are present in lamprophyer, while the 40 K was found in felsite (acid dyke). The minimum values of 226 Ra and 232 Th are found in diorite samples and the minimum percentage value of 40 K is present in dolerite samples, which indicate that values of these isotopes depend on the geochemical properties of these samples and its locations. The Fawakhir granitoid consists of the following types: quartz-diorite, granodiorite and granite 9. Ten selected samples of different types of Fawakhir granitoid; granite, granodiorite and quartz-diorite were measured. From the obtained results, it is evident that radium-226 activity concentrations range from 28.3 ± 2.7 to 65.2 ± 4.6 Bq/kg with the average value of 47.6 ± 4 Bq/kg. Thorium-232 activity concentrations vary in parallel with radium-226 in the range from 22.9 ± 3 to 60 ± 5.7 Bq/kg with an average value of 44.7 ± 4.7 Bq/kg. Potassium-40 was in the range of ± 33.1 to ± Bq/kg with an average value of ± 76.7 Bq/kg. The correlation factor between 232 Th and 226 Ra, was found as It is evident from the results that the minimum values of 226 Ra, 232 Th and 40 K are found in quartz-diorite where the maximum are present in granite. The mean contents of the three isotopes have been calculated which shows that these values increase from quartz diorite to granodiorite to granite for 226 Ra and 232 Th and nearly for 40 K. As a general trend, there is a strong coherence between radium and thorium. Data show that the concentration of 232 Th is higher than that of 226 Ra. The contents and ratios show a distinct dependence on and correlation to genetic conditions. For instance, granites and granodiorites above active subduction zones have lower U, Th, and K concentrations than granites which are not above subduction zones 12. For this reason, research on U, Th and K concentrations and their ratios are used in genetic studies 13. The granites show re1atively high U contents and a distinct difference between the granitic types. Th and Ra are closely associated in granitoid rocks with nearchondritic Th/U ratio. Serpentinite rocks represents the third type of rocks under investigation in Bir El-sid area. From the obtained results of serpentinite, it can be noticed that radium-226 activity concentrations vary from 8.1 ± 1.3 to 32.3 ± 2.7 Bq/kg with an average value of 22.5 ± 2.6 Bq/kg, while thorium-232 activity concentrations show parallel trends approximately with an average value of 17.2 ± 2.7 Bq/kg. For potassium-40, the activity concentration was found in the range between 74.6 ± 7.5 and ± 74.4 Bq/kg with an average value of ± 36.9 Bq/kg. The last group of rocks was selected from the metagabbroic part of Bir El-Sid, which covers an area of about 20 km 2. From the analytical results of metagabbro it can be seen that radium-226 activity concentrations vary from 11.3 ± 1.8 to 34.9 ± 3.1 Bq/kg with an average value of 19.9± 2,34 Bq/kg, while thorium-232 activites vary from 3.7 ± 2.8 to 25.1 ±3.4 Bq/kg with an average value of 13.3 ± 2.5 Bq/kg. For potassium-40 the activity concentration was found in the range of ± 15.4 to ± 82.4 with an average value of ± 23.3 Bq/kg. Basalt rocks possess a relatively low background radioactivity level with average contents of the radium, thorium and potassium isotopes of 3.5 ± 1.3, 1.5 ± 1.1 and 21.9 ± 6.3 Bq/kg, respectively. To compare the measured activity contents of the different rock types from Bir El-Sid area, the mean activities of Ra-226, Th-232 and K-40 (Bq/kg), are plotted as a histogram (Fig. 1), where the following observations can be discussed: (1)The background radioactivity varies greatly among the various rock types. It is clear that the basic rocks, represented in the area of study by basalt, basic dyke and metagabbro, possess lower mean values of Ra, Th and K than acidic dyke (felsite) and intermediate dyke (lamprophyer); (2)the results indicate that K-40 exhibits the highest activity fraction compared to Th-232 and Ra-226.

4 212 INDIAN J PURE & APPL PHYS, VOL 44, MARCH 2006 The concentration of K-40 in igneous rocks varies roughly with the abundance of silica in those rocks. In sedimentary rocks, the concentration of K-40 depends upon the relative amounts of feldspar, mica and clay minerals that make up the mineral-aggregate sediments; (3)also the results show the presence of a strong coherence between thorium-232, radium-226 and potassium for all rock types, where they reach their maximum values in fawakhir granitoid and minimum values in basalt. Generally, it is found that the concentrations in common igneous rocks are distinctly higher in acidic (granite, granitoid, felsite) than in ultrabasic rocks (basalt, dolerite), which are in fair agreement with some previous results 14. Fig.1 Mean activity concentration in (Bq/kg) from different rock samples

5 AHMED et al.: NATURAL RADIOACTIVITY OF SOME SELECTED ROCKS 213 The tectonic infrastructure of the Wadi El-Gemal area crops out in a belt trending 15 NW-SE. It is differentiated into the following rock units 16. Hornblende gneisses, gneissose granite complex and mica schists. The major portion of the mapped area is covered by suprastructure rocks. The suprastructure tectonic unit comprises two subsidiary rock units 16, besides ophiolite suite (including serpentinite and metagabbros) and low-grade ophiolitic melange. Six pink and four alkali granites were selected from gneissose granite complex -Wadi El-Gemal. From the results it is evident that the pink granite samples possess mostly higher values of activity concentration compared with allkali samples. For pink granite, these values change from 24.9 ±2.5 to 59 ±3.9 and from 27.6 ±3.4 to 75.9 ± 7.8 (Bq/kg) and from 970 ± 70.9 to 1280 ± 94.1 (Bq/kg) for U-238, Th-232 and K-40, respectively. The corresponding values of alkali granite samples are from 21.8 ±2 to 53.7 ±4.3 (Bq/kg) and 21.8 ±2.6 to 28.8 ±3.4 and 551 ±10.9 to 1114 ±81.1 (Bq/kg). From the values of the content, it can be noticed that these values are higher in case of pink colour than the corresponding values of the alkali granite samples, with correlation factor between U and Th The average uranium and thorium contents for the pink granites in Wadi El-Gemal area are similar to the values given by Rogers and Adams 17 for granitic rocks. The slightly lower values for uranium (3.2 for gneissose granites versus 4 ppm) and thorium (11.8 versus 18 ppm) may reflect the inclusion of slightly less silicic rocks 16. These latter differences may reflect a preferential enrichment of thorium relative to uranium during granite genesis or a secondary depletion of uranium relative to thorium after crystallization of granites 18. The average U content of alkalic granite under investigation (2.8 ppm) is similar to the value of 3 ppm measured in Abu Marw area, Southeastern Desert, Egypt 19, but thorium contents are lower. Seven serpentinite, eight metagabbro and menalge samples which represent ophiolite rocks are selected for the radioactivity measurements. From the obtained results it can be seen that the radium-226 activity concentration in serpentinite is in the range from 2 ± 0.7 to 11.7 ± 1.6 Bq/kg with an average value of 6.2 ± 1.4 Bq/kg. The activity of thorium-323 varied from 1.9 ± 0.7 to 11.2 ± 1.6 Bq/kg with an average of 6 ± 1.6 Bq/kg, while the activity of potassium-40 varied from 31.9 ± 6.5 to 203 ± 16.4 Bq/kg with an average value of 84.5 ± 9.2 Bq/kg. In metagabbros, the average values of radium-226, thorium-323 and potassium-40 are 9.4 ± 1.8, 5.6 ± 1.8 and 239± 19.4 Bq/kg, respectively. With respect to menalge, which exhibits higher activities than metagabbro and serpentinite, the activity of radium-226 ranges from 1.8 ± 0.8 to 18.5 ± 2.3 with a mean value of 11.1 ± 1.8 Bq/kg, while for thorium-232 and potassium-40 the mean values are 8.9 ± 2 and 376.9± 29.3 Bq/kg. No correlation factor between U and Th was found. Amphibolites are metamorphic rocks, which predominantly consist of amphibol + plagioclase. From the values of activity concentration (Bq/kg) in amphibiolite samples, where it is clear that the radioactivity is generally low. According to Billings 20, the low level of thorium content may be due to a selective loss of thorium during metamorphism. Dykes are defined by a long and relatively thin mass of eruptive rock, which during its molten state intruded and created cracks in other rocks and which may contain mineral deposits located between the rock masses. In this area (Wadi El-Gemal), the gneissose granites are generally traversed by a number of dykes and veins of different ages, composition and thickness. They are represented mainly by aplite and basic dykes as well as quartz and pegmatite veins. Also, the fine-grained hornblende gneissess are dissected by a great number of pegmatite and quartz veins and granitic dykes 16. From the measured and calculated values of Dyke rocks in Wadi El-Gemal, it is clear that the highest values are found in the acid rock compared with the intermediate or basic types which is same case of Bir El-Sid area. To compare the measured activity concentrations of the different rock types from the Wadi El-Gemal area, the average values of U-238, Th-232 and K-40 activities are plotted as a histogram in Fig. 1. From the results, it can be seen that the lowest values of activity concentration (Bq/kg) are found in basic dyke rocks, except for potassium where its percentage value is nearly the same for basic and amphipiolite. The highest activity values of Ra and K are found in acid dyke rocks, while for Th it is found in granite rocks. But the highest values of concentration is found in acidic dyke for Ra and K and Th in granite rocks which also coherence between Ra and Th as it is clear in the case of Bir El-sid area. Fifteen rock samples were collected from different locations in Germany. Fig. 1 shows the average activity of these samples. From the results, we can

6 214 INDIAN J PURE & APPL PHYS, VOL 44, MARCH 2006 see that for granit rocks, the average activity concentration values for the natural radionuclides 226 Ra and 232 Th are 76.1 ±5.1 and 70 ±6.5, respectively which are higher than the Earth s crustal average (37.8 Bq/kg and 49 Bq/kg) for radium and thorium 4. The granites along with being potassium rich, are also usually uranium and thorium rich while the ultramafics are lean in all three elements 7. As in the case of the results of Bir El-Sid and Wadi El- Gemal areas, the lowest values of activity and concentration are in amphibolit, while the highest values are found in granite for uranium thorium and potassium. 3.1 Comparison between the radioactivity of Bir El-Sid, Wadi El-Gemal areas and Germany To compare between the concentrations of radium. thorium and potasium in different rock types of Bir El-Sid, Wadi El-Gemal and samples collected from Germany, the averages of these elements in (Bq/kg) are calculated and listed in Table 1. The results indicate that the mean values of U, Th and K for granite. acid dyke and dolerite rocks in samples collected from Germany are higher than the values in Wadi El-Gemal and Bir El-Sid areas, while the corresponding values in serpintinite, diorite and lamprophyer are less. In serpentinite, metagabbro and granite rocks, the values of Ra, Th and K in Bir El-Sid area exceed its values in Wadi El-Gemal area. In basic rocks, Ra and Th in Bir El-Sid area are higher than the values in Wadi El-Gemal area, while for K there is no distinct difference between the two regions. In case of granite, the mean activity values, (Bq/kg) of radium. thorium and potassium are higher than the corresponding values in other rock types in areas under investigation. The granites have the percentage of SiO 2, Al 2 O 3 K 2 O and Na 2 O higher than the corresponding values in other rock types in two areas. The high values of Ra, Th and K measured in two areas can be attributed to the high positive correlation between these elements and Fe 2 O 3, Al 2 O 3. K 2 O and negative correlation with CaO and MgO which explains the higher values of Ra, Th and K in granite rocks in two areas. There are great fluctuations of K, Th and Ra contents of granites. Some parts of the earth s crust seem to be much enriched in Th and Ra. This is expressed by the fact that granites of these areas. although differing much in age, all have elevated contents of the radioactive isotopes. However, such Table 1 Mean activity concentration of Ra-226, Th-232 and K- 40 (Bq/Kg) from different rocks in areas under investigation Type of rock Ra-226 Bq/Kg Rock Bir El-Sid Wadi El-Gemal Germany Granite 57.4 ± ± ±5.1 Serpentinite 22.5 ± ± ±1.7 Metagabbro 19.9 ±8 9.4 ± ±2.3 Acid dyke ± ± ±4 Lamprophyer 37.2 ± ± ±4.1 Diorite 12.4 ± ±2 Dolerite 14.5 ± ± ±3.5 Amphibolite 10.4 ± ±1.8 Th-232 Bq/Kg Granite 53.4 ± ± ±6.5 Serpentinite 17.2 ±2.7 6 ± ±1.4 Metagabbro 13.3 ± ± ±3.2 Acid dyke 28.6 ± ± ±4.8 Lamprophyer 38.8 ± ± ±3 Diorite 8 ± ±1.5 Dolerite 8.9 ± ± ±3.8 Amphibolite 4.8 ± ±1.7 K-40 (Bq/kg) Granite ± ± ±106.8 Serpentinite ± ± ±7.2 Metagabbro ± ± ±85.1 Acid dyke 884 ± ± ±150.4 Lamprophyer 601 ± ± ±47.3 Diorite ± ±15.7 Dolerite ± ± ±54.6 Amphibolite ± ±7.2 notably high radioactivity may be attributed to several factors such as the presence of relatively increased amount of accessory minerals, the increase of radioactivity with the degree of acidity of these rocks, the relatively increased content of the radioactive potassium isotope 40 K. 4 Conclusion The mean values of 226 Ra, 232 Th and 40 K for granite, acid dyke and dolerite rocks in samples from Germany are higher than the values of those from Egypt, while the corresponding values of serpentinite, diorite and lamprophyre are lower. In case of granite, the mean activity values (Bq/kg) of radium, thorium and potassium are higher than the

7 AHMED et al.: NATURAL RADIOACTIVITY OF SOME SELECTED ROCKS 215 corresponding values in other rock types in areas under investigation. At the same time, the granite has the percentage of SiO 2, Al 2 O 3, K 2 O, and Na 2 O higher than the corresponding values, in other rock types in two areas. The high values of Ra, Th and K measured in two areas can be attributed to the high positive correlation between these elements and Fe 2 O 3, Al 2 O 3, K 2 O and negative correlation with CaO and MgO which explains the higher values of Ra, Th and K in granite rocks in two areas. Finally, from the general tendency for the main rock groups two comments should be made: the radioactivity of igneous rocks increases from basic to acid rocks and the radioactivity of sedimentary rocks increases from clean to shaly rocks. i.e.. with increasing clay content References 1 Adams J A, Loweder W M & Thomas F G, The natural radiation environment II ( Rice University and the University of Texas School Public Health), Adams J A &. Loweder W M, The natural radiation environment (University of Chicago, Chicago), International Atomic Energy Agency, Uranium deposits in metamorphic rocks Vienna (1989). 4 Ajayi O S, Health Phys, 79 (2) (2000). 5 Voutilainen A, Castren O, Makelainen I, Winqvisk K & Arvela H, Radia Protect Dosim 24 (1988) International Atomic Energy Agency Proceedings of an IAEA meeting on uranium exploration methods, Vienna, Larson E S, Phair G, Gottfied D & Smith W L, US Geol Survey Prof. Paper:65-74 (1956) Hamilton E I & Ahrens L H, Applied Geochron; (Academic Press, London &New York ), Mohamed O M, Egypt; M. Sc. Thesis, Assiut University, Egypt (1993). 10 Noorddin I, Journal of Environmental Radioactivity 43, (1999). 11 Knoll G F, Radiation detection and measurement. Second edition: (John Wiley, New York ), Haack U, Radioactivity of rocks; Chapter 7 in: Landolt- Börnstein Numerical Data and Functional Relationships in Science and Technology (K-Hellwege,ed.), New Series; Group V. Geophysics and space research, Vol.1 Physical properties of rocks, supvolume b, (Sprenger-Verlag Berline Heidelberg, New York ) Simov S D, IAEA; Uranium deposits in metamorphic rocks, Vienna (1989). 14 Helbig K & Treitel S, Handbook of geophysical exploration, seismic exploration V.18, Ch.5, Elsevier Science Ltd (1996) 15 Ahmed A, Ph.D. Thesis (Assiut University, Egypt ), Hussien H A M, Ph.D. Thesis (Assiut University, Egypt), Rogers J J W & Adams J A S, Uranium In Wedepohl K H, ed., Handbook of geochemistry, Vol.II/5,(Springer, Berlin) 92E-92M (1969). 18 Stuckless J S &Vantrump J, Proceedings of the symposium on uranium exploration methods, review of the NEA/IAEA R&D programme, Paris (1982). 19 Falham O M, MSc. Thesis, (South Valley University, Egypt ), Billings G K, A geochemical investigation of the Vakkey Spring geiss and Packsaddle schist, Llano Uplift, Texas, Texas J Sci,14:328-51(1962).