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

Abstract

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 km². Uranium and thorium isotopes were determined by alpha spectrometry. The activity concentrations of ²³⁸U, ²³⁴U and ²³⁵U 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 ²³²Th, ²³⁰Th and ²²⁸Th 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 ²³⁰Th/²³²Th activity ratios in all samples were lower than 20, indicating that these samples have been contaminated by detrital ²³⁰Th. 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. ²³⁴U/²³⁸U 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.