226Ra,232Th and 40K contents and radon exhalation rate from materials used for construction and decoration inCameroon

Abstract

This work deals with the measurement of radioactivity and radon exhalation rate frombuilding materials manufactured in Douala city from geological materials. Ninetypes of building material were surveyed for their natural radioactivity contentsusing high-resolution gamma-ray spectrometry. The activity concentrations for226Ra,232Th and40K variedfrom 11.5 to 49 Bq kg−1, 16 to 37 Bq kg−1 and 306 to 774 Bq kg−1, respectively. The absorbed dose rate in the samples investigated at 1 m above ground level ranged from28.5 to 66.6 nGy h−1. External and internal hazard indices were also estimated as defined by the EuropeanCommission. The Ra equivalents of the materials studied ranged from 57.5 to133 Bq kg−1 and are much smaller than the recommended limit of370 Bq kg−1 for construction materials for dwellings.Polycarbonate nuclear track detectors (NTDs), type CR-39, were used for measuring theradon concentration from different materials. In fact, knowledge of the radon exhalationrate from building materials is important for understanding the individual contribution ofeach material to the total indoor radon exposure. Samples were hermetically closed inglass vessels and the radon growth was followed as a function of time. The radonexhalation rate was therefore derived from the experimental measurement ofα-track densities. The radon exhalation varied from(5.77 ± 0.06) × 10−5 to(7.61 ± 0.07) × 10−5 Bq cm−2 h−1 in bricks,from (5.79 ± 0.05) × 10−5 to(11.6 ± 0.12) × 10−5 in tiles,and was (6.95 ± 0.03) × 10−5 Bq cm−2 h−1 in concrete. A correlation (correlation coefficient ) was found between radium concentration measured with a HPGe detector and the radonexhalation rate obtained using nuclear track detectors.