Assessment of radiological hazard of NORM in Margalla Hills limestone, Pakistan

Studies on naturally occurring radioactive material (NORM) in the limestone from the Margalla Hills have been carried out by measuring gamma activity and to access its radiological implications if any. For data acquisition, a High-Purity Germanium detector was employed. The activity concentrations of Ra-226, Th-232, and K-40 were found to be 14.32 +/- 0.24, 2.05 +/- 0.04, and 13.80 +/- 0.20 Bq kg(-1), respectively. These values are relatively lower as compared to that in the limestone of other countries and much lower than the values reported for the natural building stones. The average specific activities due to Ra-226 were found to be higher when compared with K-40 and Th-232. Indices of radium equivalent activity (Ra-eq), internal hazard (H-in), indoor absorbed gamma dose rate (D-R,D-), and corresponding annual effective dose (E-eff) were also determined for the limestone-made rooms. All of these indices were found to be in the lower ranges. The Margalla Hills limestone does not pose any excessive radiological health hazard as a building material and in industrial uses for a common man.