Determination of natural radioactivity in building materials used in the Karachi area by γ-ray spectrometry and INAA

Samples of sand, stone and manufactured building materials collected from Karachi area have been analyzed for the primordial natural radionuclides U-238, Th-212 and K-40 using gamma-ray spectrometry. The uranium and thorium contents have also been determined by instrumental neutron activation analysis (INAA). The specific activities in these materials, having a radium equivalent activity less than 370 Bq kg(-1), when evaluated for radiological effects show that all materials meet the external gamma-ray dose limitation of 1.5 mSv y(-1). The gamma-ray spectrometric and INAA techniques complemented each other well in this study.