Natural Radioactivity and Radon Exhalation from Building Materials in Underground Parking Lots

The change of natural ionizing radiation and the radon exhalation rates from typical building materials in underground parking lots are presented in the article. The activity concentration of natural radionuclides Th-232, Ra-226, and K-40 in six important types of construction materials, which are mostly used in Lithuania, were analyzed using high-resolution gamma spectroscopy. The highest values were found in concrete and ferroconcrete samples: Ra-226 44 and 90 Bq kg(-1); Th-232 29 and 34 Bq kg(-1); K-40 581 and 603 Bq kg(-1). A strong positive correlation (0.88) was observed between radium activity concentration and radon concentration. The activity indexes (I-alpha and I-gamma) and radium equivalent activity (R-eq) evaluating the suitability of materials for such constructions from the view of radiation safety were determined. The average values of the calculated absorbed dose rate in samples ranged from 18.24 nGy h(-1) in the sand to 87.26 nGy h(-1) in ferroconcrete. The calculated annual effective dose was below the limit of 1.0 mSv y(-1). The values of the external and internal hazards index (H-ex and H-in) were all below unity, and the values of I-gamma and I-alpha were below the recommended levels of 0.5 and 1. Dosimetric analysis of underground parking lots was carried out. It was determined that the external equivalent dose rate caused by the Rn-222 progeny radiation in the underground car parking lots varies from 17 to 30% of the total equivalent dose rate.