XA9745962 ENVIRONMENTAL IMPLICATIONS OF THE LABORATORY GAMMA RAY SPECTROMETRIC MEASUREMENTS MADE ON THE BLACK SAND BEACH DEPOSIT OF THE ABU KHASHABA RADIOACTIVE PROSPECT, ROSETTA, EGYPT A.M. ELSIRAFE, H.A. HUSSEIN, R.A. ELSAYED Nuclear Materials Authority of Egypt, El Maadi, Cairo A.M. SABRI Geophysics Department, Faculty of Science, Ain Shams University, Cairo Egypt Abstract Laboratory gamma-ray spectrometric measurements carried out on the surficial black sand beach deposits of Abu Khashaba radioactive prospect located 5km east of Rosetta, north Nile Delta, as a part of the comprehensive exploration and assessment program of these radioactive placer deposits has generated a vast amount of radiometric data. These data, initially used for radioelement exploration, provided valuable baseline information necessary for environmental studies and monitoring the impact of any potential environmental radioactive pollution that might occur as a result of nuclear activities in the surrounding regions. Analysis of the acquired spectrometric measurements indicated that both thorium and uranium are the two radioelements that significantly contributed to the measured total natural gamma-ray flux, rather than potassium. This is mainly attributed to the nature of the mineralogical composition of these beach deposits. On the other hand, qualitative interpretation of the produced maps of the three radioelements: potassium, uranium and thorium, supplemented by the examination of their frequency distributions and application of the homogeneity statistical chi-squared test has shown pronouned uranium and thorium comparable zonal distribution patterns that are consistent with the spatial distribution of the heavy mineral concentrations in the studied black-sand deposits. In contrary, these deposits showed uniformally distributed potassium concentrations all over the studied area of Abu Khashaba beach. The two identified radiometric zones displayed a normally distributed uranium and thorium concentration distributions and a contrasting mean background concentration values for these two elements. Concentrations of natural radioelements: potassium, uranium and thorium in the investigated radioactive black-sand deposits were used in producing the environmental total gamma radiation exposure rate map of the studied Abu Khashaba beach and estimation of the mean background levels of the total gamma radiation dose rates.Two zones of contrasting average gamma exosure rates were outlined over the studied Abu Khashaba beach. The first zone displayed an average exposure rate of 13.9 /*R/h (average dose rate 115.6 millirem/year) whereas, the second zone displayed a relatively lower average exposure rate of 3.9 fiR/h (average dose rate 32.1 millirem/year). The estimated average total gamma dose rates remain in the safe side and within the maximum permissible safe radiation dose without harm to the individual. However in order to have better information about the actual levels of radiations, the contributions from other radionuclides that have not been taken into account should be considered. 1. INTRODUCTION 1.1. Genesis, Mineralogy and Distribution of the Egyptian Black-Sand Deposits The Egyptian black-sands are beach placer deposits formed by the mechanical concentration of resistant minerals released by weathering of the Precambrian igneous and metamorphic source rocks of the upper reaches of the River Nile. These erosional products have been carried down through the course of the Nile, and were subjected to natural physical and chemical separation and sorting during transportation. By normal surface processes, mainly the combined effect of waves and wind, these transported weathering products were accumulated to form huge deposits, intermittently and in variable proportions, occupying the beach of the Mediterranean Sea of Egypt along a stretch of about 350 km long, extend from El Arish eastwards to Abu Qir westwards. The geology of these 389 deposits along the Mediterranean coast is directly related to the development of the Nile Delta and the past configuration of the Nile branches [1]. The Egyptian black-sands has drawn an increasing interest since they contain different concentrations of potentially economic heavy minerals that are considered as nuclear raw materials as well as their importance in many of the metallurgical industries. The Egyptian black-sand deposits are loose fine sands consisting a complex mineral associations of light and heavy fractions. The light mineral fraction is mainly consists of quartz which is the principal constituent (average 95%) and felspars which constitute about 5% of this fraction. The percentage of the heavy mineral fraction varies from 8% up to 97% of the total mineral constituents of the black sands. This fraction is mainly formed of a complex association of minerals characterized by their dark color and high specific gravity. The most abundant of these minerals are: ilmenite, magnetite, zircon, garnet, rutile and monazite. Other minerals are also present, but in trace amount such as chromite, cassiterite, wolframite, corundum, beryle, uranothorite and gold [1 and 2]. 1.2. Location and General Topography of Abu Khashaba Beach Abu Khashaba beach occurs in the extreme northwestern corner of the Nile Delta, on the Mediterranean Sea coast (Fig. 1). It is situated 5 km to the north of Rosetta (Rashid) City and lies on the eastern side of Rosetta branch of the River Nile, about 7.5 km from the estuary. This area represents the most wider coastal plain, extends for about 2.5 km in the back beach. The present zDITERRANEAN S 31 00 -31 00' X 00' 31 00 Scale 1 : lpOO.OOO >...,... : FIG. 1. Map of north Nile Delta, Egypt. The arrow points to location of the studied part of Abu Khashaba beach, east of Rosetta (Rashid) city. 390 study is only restricted to the western part of Abu Khashaba beach (Fig. 1) and covers a total surface area of 2.4 km2. The altitude of Abu Khashaba area is slightly higher than the sea level, and the topography is ahnost flat where the coastal plain occupies most of the surface except the southern part where accumulations from eolian sands occur as small dune belts and sand bars. The highest concentration of the heavy minerals along the Mediterranean coast of Egypt is found along Abu Khashaba beach where these extend eastward for a distance of about 40 km along the coast (Fig. 2). These conditions favour the area of Abu Khashaba beach as a good prospect for radioactive raw materials. 1.3. Scope and Objectives of the Study Environmental monitoring and meaningful interpretation of man-mad radioactive pollution is impossible without knowledg about the natural abundance of the radioelements and the natural background radioactivity leveles in the environment [3]. In that regard comperhensive assessment program of the mineral potentials of the radioactive black sand deposits of Abu Khashaba prospect, carried out by the Egyptian Nuclear Materials Authority, provided a vast amount of potassium, uranium and thorium concentration measurements acquired from the systematic aerial, ground and laboratory gamma-ray spectrometric measurements conducted over these beach placer deposits. The present research work aims essentially to make use of the laboratory spectral gamma-ray measurements, in establishing the environmental natural gamma radiation levels along the suveyed Abu Khashaba beach. This will provide baseline information necessary for the detection and determination the amount and extent of potential environmental changes in the terrestrial background radiation that might result from nuclear testing or accidents involving release of nuclear radiations and accompanied radioactive contamination of the ground. FIG. 2. Photomap of north Nile Delta, Egypt produced by the processing of the digital data acquired with the Landsat Satellite Multispectral Scanner (MSS) of resolution 82 x 57 m, restored to 50 x 50 m. This map has been produced by the Egyptian Remote Sensing Center, Cairo. Black-sand deposits (white to light blue colored zones) extend along andparrallel to the Mediterranean shoreline, east of Rosetta (Rashid). 391 2. FIELD WORK (SAMPLING PROCEDURE) A total of 272 samples, representing the upper 50 cm of the black-sand depoists at the eastern part of Abu Khashaba beach (2.4 km2), were collected on a quadrate grid pattern using 100 m sampling interval. The regular grid pattern of sampling was designed to overcome the variability in the heavy mineral content of these black-sand deposits. These samples were taken by forcing a cylindrical rigid plastic tubes, 50 cm length and 2.5 cm diameter, vertically into the ground at the sampled location. In this way continous core samples from the sampled locations were obtained. Tubes were then sealed and labeled. 3. LABORATORY GAMMA-RAY SPECTROMETRIC MEASUREMENTS 3.1. Sample Preparation Preparatory processes were carried out on the collected black-sand samples as a necessary step prior to the execution of the laboratory spectral radiometric measurements. In that regard each sample was thoroughly rubbed and mixed well in order to avoid the non-homogeneity in the distribution of its mineral constituents. Then a proper weight (300-350 gm) of each sample was placed in standard- size cylindrical plastic container 9.5 cm in diameter and 3 cm height. These containers were carefully sealed to prevent contamination. Samples in the sealed containers were stored for three weeks where the radon buildup is back to the normal state and attains radioactive equilibrium. 3.2. Instrument