Alpha spectrometry isotopic ratios indications in the Paleozoic sedimentary rock of El Gor area, Southwestern Sinai, Egypt: insights on uranium mobility age.

The study area is located between longitude 33° 18' 00" - 33° 21' 00" E and latitude 28° 59' - 29° 01' N and covers approximately 700 km 2 . Uranium and thorium isotopes were determined by alpha spectrometry. The activity concentrations of 238 U, 234 U and 235 U were ranged between 245.5 ± 8.3-465.2 ± 15.2 Bq.kg -1 with an average 345.5 ± 10.4-452.5 ± 9.3 Bq.kg -1 and 890.5 ± 21.3 Bq.kg -1 with an average 632.3 ± 14.9-11.40 ± 0.5 Bq.kg -1 and 21.50 ± 1.4 Bq.kg -1 , respectively. The activity concentration of 232 Th, 230 Th and 228 Th were ranged between 153.1 ± 0.3-318.1 ± 2.9 Bq.kg -1 , 149.5 ± 0.7-280.8 ± 2.2 Bq.kg -1 and 36.9 ± 0.1-60.5 ± 0.9 Bq.kg -1 . The 230 Th/ 232 Th activity ratios in all samples were lower than 20, indicating that these samples have been contaminated by detrital 230 Th. Th/U ratio varied between 1.3 and 2.1 with an average 1.8; all values were lower than 3.5, indicated enrichment of uranium. 234 U/ 238 U activity ratios that higher than unity indicates that an isotope of uranium has migrated within the rock. From the isotopes of uranium and thorium and their activity ratios, the isochron age for the collected samples was about 58.96 ka.