Gamma-ray measurements of natural radioactivity in sedimentary rocks from Egypt

摘要

The aim of this study was to measure concentrations and distributions of natural radionuclides occurring in rocks. The activity concentrations (Bq·kg~(-1)) of the naturally occurring radionuclides ~(226)Ra, ~(232)Th, and ~(40)K in sedimentary rock samples from Eastern Desert (Um El-Huetat), Nile Valley (Gebel Owina) and from southwest Sinai (Wadi Ghweiba) were measured using a high-purity germanium detector. The samples under investigation (clay, shale and sandstone) were used as raw materials in the construction industry (bricks, ceramics, cement, fillers, etc.). Though the sediments of Egypt have already been investigated in the geological and mineralogical aspects, it is necessary to investigate the natural radioactivity in order to complete their classification. The average concentration values of ~(226)Ra, ~(232)Th, ~(40)K in the surveyed samples were 47 ± 7, 21± 5, 393±19 Bq·kg~(-1) (clay); 23 ± 5, 30 ± 6,563 ± 24 Bq·kg~(-1) (shale); and 17 ± 4, 14 ± 4, 299 ± 17 Bq·kg~(-1) (sandstone), respectively. All sediment samples have radium equivalent activities ranging from 55 to 115 Bq·kg~(-1), lower than the limit set in the OECD Report (370 Bq·kg~(-1)). The overall mean outdoor terrestrial gamma dose rates fluctuate from 28 to 55 nGy·h~(-1). The external gamma radiation dose due to natural radionuclides present in the samples have been computed and compared with the global averages. In terms of the radiation safety, the natural radioactivity of the sediment in Egypt is below the recommended limits of the gamma dose rate. Therefore, they can be used for all kinds of public buildings.