Measurement of radioactivity and radon exhalation rate in different kinds of marbles and granites

Geological materials usually contaminated with naturally occurring radioactive materials (NORM) have become a focus of great attention. These NORM under certain conditions can reach hazardous contamination levels. Some contamination levels may be sufficiently severe that precautions must be taken.

The present study deals with 60 geological samples (marble and granite) from both Egyptian and foreign locations. The studied samples were analyzed and the concentrations in Bq/kg dry weight of radioisotopes were determined by gamma-ray spectrometry using hyper-pure germanium (HPGe) detector in Bq/kg dry weight. The absorbed dose rate due to the natural radioactivity in the samples under investigation ranged from 2.45±0.07 to 64.44±1.93 nGy/h for marble and from 41.55±1.25 to 111.94±3.36 nGy/h for granite. The radium equivalent activity varied from 5.46±0.16 to 150.52±4.52 Bq/kg for marble samples and from 229.52±6.89 to 92.16±2.76 Bq/kg for granite. The representative external hazard index values for the corresponding samples are also estimated and given.

The radon exhalation rates for marble and granite samples were also calculated by using solid state nuclear track detector (CR-39). The value of radium exhalation rate varied from 8.0±2.39 to 30.20±5.06 Bq/m²/d for marble and 6.89±1.72 to 25.79±4.38 Bq/m²/d for granite and the effective radium content was found to vary from 1.700±0.51 to 6.42±1.08 Bq/kg for marble and 1.29±0.32 to 5.63±0.96 Bq/kg for granite. The values of the radon exhalation rate and effective radium content are found to correspond with the values of uranium concentration measured by the HPGe detector in the corresponding sample.