Assessment of Exposure Due to Technologically Enhanced Natural Radioactivity in Various Samples of Moroccan Building Materials

Abstract

The aim of our present work is to measure the specific activities of the radionuclides 226 Ra, 232 Th, 40 K and the exhalation rates in terms of area and mass of 222 Rn in some samples of building materials commonly used in Morocco in order to evaluate the radiological risk caused by natural radioactivity. To this end, the analyses were carried out, using two nuclear techniques, namely high resolution gamma spectrometry and alpha dosimetry based on the use of LR115, on 50 samples collected from large commercial suppliers in Morocco. The results of these analyses show that the average specific activities of 226 Ra, 232 Th and 40 K in these materials vary from 9 to 52 Bq/kg, 3 to 63 Bq/kg and 68 to 705 Bq/kg respectively. These activities remain within the permissible limits of 35 Bq/kg, 30 Bq/kg and 370 Bq/kg respectively, with the exception of a few samples of red brick, gray cement, ceramic and granite. The activity of the radium equivalent ( Ra eq ), the internal ( H in ) and external ( H ex ) hazard indices, the absorbed dose rate , the total annual effective dose , the excess lifetime cancer risk (ELCR) as well as volumic activities, exhalation rates in terms of area ( E S ) and mass ( E M ) are calculated for the samples analyzed in this work in order to assess the radiological risks resulting from the use of these materials in various construction activities. It seems that the values of these indices vary from 19 to 196 Bq/kg, 0.08 to 0.67, 0.05 to 0.53, 9 to 91 nGy/h, 0.05 to 0.56 mSv/y, 0.19 × 10 − 3 to 1.96 × 10 − 3 , 72 to 350 Bq/m 3 , 56 to 273 mBq ⋅ m − 2 ⋅ h − 1 and 3 to 15 mBq ⋅ kg − 1 ⋅ h − 1 respectively. The lowest values are identified for gypsum, while the highest are attributed to granite. All of the obtained results of these indices respect the permissible limits except for the Ra eq in some granite samples, the ELCR index in all samples except gypsum and the radon volumic activity in some gray cement samples, ceramic and granite. As a result, the different types of building materials analyzed in our work do not present a health risk to the public and can be used in various construction activities, with the exception of a few samples of red brick, gray cement, ceramic and granite. The choice of the use of red brick, gray cement and ceramic should be monitored and adapted according to the criteria of the limitation of the doses whereas the use of the granite must be moderate in order to limit over time the health risk which increases with the duration of exposure of humans to these building materials.