Natural radioactivity and radiological hazard assessment of Egyptian oil ashes

Oil fly and boiler ash samples were collected from the four major Egyptian power plants in order to determine their natural radioactivity. Secular equilibrium between U-238 and Th-232 and their decay products is significantly disturbed in oil ash samples. The Ra-226/U-238 ratios were between 440 and 1993 with an average value of 801, indicating that the concentrations of daughters Ra-226 were very high compared to the parent U-238 in the oil ash samples. While, the average ratios for Pb-210/Ra-226 in most samples were 1.19 +/- 0.05, indicating a secular equilibrium in the Ra-226-Pb-210 sub series. The natural radioactivity due to U-238 and Th-232 was found to be negligible. While the activity concentrations of Ra-226 ranged from 3205 to 12,320 Bq kg(-1) with an average value of 9284 Bq kg(-1), Pb-210 ranged from 5960 to 13,930 Bq kg(-1) with an average value of 11,513 Bq kg(-1). The results are compared with the reported data from other countries. The average value of radium equivalent activity was 9308 +/- 2729 Bq kg(-1), while the external and internal hazard indexes were found to be 25 +/- 7 and 50 +/- 15, respectively. All the studied radiological parameters were higher than the recommended limit by the IAEA in all ash samples.