This study aimed to the assessment of the activity concentrations and radiation hazard indices with excess lifetime cancer risk (ELCR) in twenty one sedimentary rock samples obtained from three different localities, southwestern Sinai, Egypt. The natural radionuclides have been measured by using HPGe detector with a specially designed shield. The results of this study showed that the activity concentrations of 238U, 226Ra, 232Th and 40K were higher than the world's average levels. The activity ratios 234U/238U, 230Th/238U, 230Th/234U, 226Ra/238U, 238U/235U and 234U/235U were calculated to estimate the radioactive equilibrium / disequilibrium in the three localities. The radium equivalent (Raeq) in Bq/Kg, external hazard index (Hex), radioactivity level index (I γ), the absorbed dose rate (D) and the annual effective dose (AED) in outdoor environment were estimated. The excess lifetime cancer risk (ELCR) was found to be high for all samples due to high natural radioactivity concentrations in the area under investigation which represent radiological risk for the health of population.
