Distribution of Natural Radionuclides in Ama Fatma oil shale, Morocco

The present work aims to analyze the distribution of radionuclides naturally occurring in the oil shale of the Ama Fatma coastal zone. For this purpose, using gamma-ray spectrometry, we analyzed the activity concentrations of uranium (U), thorium (Th) series, and potassium-40 (K-40) in oil shale samples retrieved from the study area. The concentrations of U-238 were ranged from 45 ±36 to 194±50 Bq.kg^-1 and those of Th-232 fluctuate between 1.48±0.92 and 9.47±1.06 Bq.kg^-1. The measured concentrations for Ra-226, Pb-214 and K-40 oscillate between 33±5 and 138±9 Bq.kg^-1, 18±1 and 68±3 Bq.kg^-1 and between 17±4 and 279±16 Bq.kg^-1 respectively. The obtained values variation appears to be related to the deposit nature and assimilation processes of appropriate radionuclides rather than to the retrieved samples’ related depth. The analysis of the ²³²Th/²³⁸U and ²²⁶Ra / ²³⁸U allowed an understanding of these radionuclides behaviors. The ratios ²²⁶Ra / ²³⁸U ranged from 0.56 to 0.74 with a mean value of 0.70 which indicates the existence of disequilibrium in the investigated oil shale samples. This disequilibrium can be attributed to significant differences in the mobility of these radionuclides.