الفهرس 
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Abstract
The natural radioactivity present in the environment is the main source of radiation exposure for humans and constitutes the background radiation level. The main natural contributors to external exposure from gamma rays are 226Ra, 232Th, and 40K. Since these radionuclides are not uniformly distributed, the knowledge of their distribution in soil, rocks and building materials play an important role in radiation protection. It is important to determine the sources and their individual contributions to the total radiation dose. The activity concentrations of uranium, thorium and potassium can vary from material to material and it should be measured as the radiation is hazardous for human health. Building materials cause direct radiation exposure because of their radium, thorium and potassium content .High concentrations of natural radionuclides in building materials can result in high dose rates indoors, from both internal and external exposure. The activity concentrations of 226Ra, 232Th and 40K have been measured for ninety two buildings samples collected from (Ten Cities) in Sohag governorate by gamma spectroscopy (sodium iodide NaI (Tl) detector) with an aim of evaluating the environmental radioactivity and radiation hazard. The detector is connected the following components: Preamplifier, main amplifier, analogue to digital convert and Canberra Multichannel Analyzer (MCA), with Genie 2000 software. This study concerned with the measurement of naturally occurring radionuclides for some building materials like redclay-brick, lime-brick, gravel, clay-brick and sand. The measured specific activity for 226Ra, 232Th and 40K are ranged from 12±1 to 70±4, 17±1to 94±5 and 142±7 to 560±28 Bqkg-1, respectively in the Clay-brick materials. While in the Gravel materials that activities ranged from 12±1 to 95±5, 11±1 to 45±3 and 70±3 to 552±28 Bqkg-1, respectively. In case of the Lime-brick materials we found that the above specific activities are ranged from 44±2 to 103±5, 43±2 to 200±10 and 100±4 to 450±13 Bqkg-1, respectively. When we investigate Red clay-brick materials for natural activities we found that, its values are ranged from 10±1 to 225±11, 17±1, to 277±14 and 176±9 to 555±28 Bqkg-1, respectively. Finally in the Sand materials when we measured its natural radioactivity we found it as follow the activities of 226Ra, 232Th and 40K are ranged from 11±1 to 51±3, 15±1 to 81±4 and 100±6 to 266±8 Bqkg-1, respectively. Absorbed dose rate in air (D), annual effective dose (AED),The measured specific activity for 226Ra, 232Th and 40K are ranged from 12±1 to 70±4, 17±1to 94±5 and 142±7 to 560±28 Bqkg-1, respectively in the Clay-brick materials. While in the Gravel materials that activities ranged from 12±1 to 95±5, 11±1 to 45±3 and 70±3 to 552±28 Bqkg-1, respectively. In case of the Lime-brick materials we found that the above specific activities are ranged from 44±2 to 103±5, 43±2 to 200±10 and 100±4 to 450±13 Bqkg-1, respectively. When we investigate Red clay-brick materials for natural activities we found that, its values are ranged from 10±1 to 225±11, 17±1, to 277±14 and 176±9 to 555±28 Bqkg-1, respectively. Finally in the Sand materials when we measured its natural radioactivity we found it as follow the activities of 226Ra, 232Th and 40K are ranged from 11±1 to 51±3, 15±1 to 81±4 and 100±6 to 266±8 Bqkg-1, respectively. Absorbed dose rate in air (D), annual effective dose (AED),radium equivalent activities (Raeq), radiation hazard index (Hin, Hex) and excess lifetime cancer risk (ELCR) associated with the natural radionuclide are calculated to assess the radiation hazard of the natural radioactivity in the building materials under investigation.