Measurement of natural radioactivity in marble found in Pakistan using a NaI(Tl) gamma-ray spectrometer

Due to the widespread use of marble as a building/construction material, experimental measurements of 226Ra, 232Th and 40K activities in marble have been carried out using a NaI(Tl) gamma-ray spectrometer with a matrix-inversion-based spectral stripping technique. The samples were collected from various geological formations in Pakistan. The IAEA reference RG-Set was used for calibration of the spectrometer. The photo-peaks at 1460.8, 1764.5 and 2614.6 keV due to 40K, 226Ra and 232Th, respectively, were used for the corresponding activity measurements. For 226Ra, 232Th and 40K, the measured activity concentrations have been found to lie in the specific ranges 4–63, 9–40 and 7–105 Bq kg−1, respectively, which are towards the lower end of the range of measurements on various geological materials world wide. The radium equivalent activity ranged from 25 to 99 Bq kg−1. Values of 0.19 and 0.26 were determined as the average external and internal hazard indices of the marble samples.