Natural radionuclides in sedimentary rocks: monitoring and radiation risk assessment

Abstract This study measures and assesses the activity concentration levels of 226 Ra, 232 Th, and 40 K using a gamma ray spectrometry system based on a high-purity germanium detector in sedimentary rocks collected from the Koya Mountains in the Kurdistan region, northeast of Iraq. The mean value of radioactivity concentrations in the rock samples varied from 2.63 ± 0.25 Bq kg −1 in gypsum rock to 378.36 ± 2.62 Bq kg −1 in marlstone for 226 Ra, from 2.53 ± 0.14 Bq kg −1 in gypsum to 28.25 ± 1.92 Bq kg −1 in claystone for 232 Th, and from 15.93 ± 2.01 Bq kg −1 in gypsum to 375.6 ± 6.31 Bq kg −1 in claystone for 40 K. The adequacy of the rock types for building purposes, considering radioactive hazards, was assessed using radiation hazard indices. The obtained results for the absorbed dose rate and the outdoor annual effective dose equivalent showed that the claystone, shale, and marlstone samples exceeded the recommended limits of 59 nGy h −1 and 70 μSv y −1 , respectively.