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

This work deals with the measurement of radioactivity and radon exhalation rate from building materials manufactured in Douala city from geological materials. Nine types of building material were surveyed for their natural radioactivity contents using high-resolution gamma-ray spectrometry. The activity concentrations for ²²⁶Ra, ²³²Th and ⁴⁰K varied from 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 from 28.5 to 66.6 nGy h⁻¹. External and internal hazard indices were also estimated as defined by the European Commission. The Ra equivalents of the materials studied ranged from 57.5 to 133 Bq kg⁻¹ and are much smaller than the recommended limit of 370 Bq kg⁻¹ for construction materials for dwellings.

Polycarbonate nuclear track detectors (NTDs), type CR-39, were used for measuring the radon concentration from different materials. In fact, knowledge of the radon exhalation rate from building materials is important for understanding the individual contribution of each material to the total indoor radon exposure. Samples were hermetically closed in glass vessels and the radon growth was followed as a function of time. The radon exhalation rate was therefore derived from the experimental measurement of α-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 radon exhalation rate obtained using nuclear track detectors.