This study aims to evaluate natural radiation and radioactivity in the rock and to assess the corresponding health risk in a region of elevated background radiation in Juban District, Ad Dali' Governorate, Yemen. The mean external gamma dose rate was 374 nGy h(-1) which is approximately six times the world average. The measured results were used to compute annual effective dose equivalent, collective effective dose and excess lifetime cancer risk, which are 2.298 mSv, 61.95 man Sv y(-1) and 8.043 × 10(-3), respectively. Rocks samples from different geological formations were analyzed for quantitative determination of (226)Ra, (232)Th and (40)K. The specific activity of the rocks samples ranges from 7 ± 1 Bq Kg(-1) to 12 513 ± 329 Bq Kg(-1) for (232)Th, from 6 ± 1 Bq kg(-1) to 3089 ± 74 Bq kg(-1) for (226)Ra and 702 ± 69 Bq kg(-1) to 2954 ± 285 Bq kg(-1) for (40)K. (232)Th is the main contributor to gamma dose rate from the rock samples. Indicators of radiological health impact, radium equivalent activity and external hazard index are 3738 Bq kg(-1) and 10.10, respectively. The mean external hazard index was ten times unity in the studied locations in Juban District, which is higher than the recommended value.
The lithology of Ibb Province Yemen (Middle East) consists of Precambrian gneissic bedrocks with post-tectonic intrusions of granite and granodiorite. The overall topography is dominated by extensive volcanic extrusions that randomly surround Ibb Province with minimal Mesozoic sedimentary outcrops. According to the Yemen Geological Survey and Mineral Resource Board (YGSMRB), the origin and age of such extrusive bodies that manifest on the surface as dikes, lava flows, and small (currently passive) cinder-cone volcanoes are of Cenozoic age associated with the rifting episode of the Arabian Peninsula and subsequent opening of the Red Sea. The overall aerial extension of the volcanic extrusions diminishes further east towards Hammam-Damt (Al'Dali Province) with a noticeable shift in magma composition from basaltic to rhyolitic. The regional aquifer, a vital source of drinking water, seems to possess similar hydrogeological properties across the Province. However, physical surveys of watersheds, stream patterns, passive pumping stations, and active freshwater wells suggest that unlike rhyolitic rocks, Basaltic rocks are non-vesicular type, dense and having no apparent hydraulic conductivity and in view of these unique lithological characteristics, do not promote groundwater recharge. Also considering extensional geomorphic control on the drainage pattern, it is possible that investigated drainages are fault or structure-controlled and provide a significant constraint on groundwater flow. Therefore, an assessment of such a geomorphological disadvantage was conducted by correlating with terrain geomorphology, bedrock composition, stream patterns, and hydrologic conductivity observed in water wells. Geological Constraints Map 4. Geology Of Yemen References Al-Eryani. Mohamed. (2011). Yemen's Water Crisis: Understanding the Causes and Designing the Solution.
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