Radium equivalent activity concentrations in concrete building blocks in eight cities in Southwestern Nigeria.

The radioactivity concentrations of (226)Ra, (232)Th and (40)K were measured by using gamma ray spectroscopy in 130 concrete building blocks collected from block making sites in eight cities in Southwestern Nigeria. The results were used to compute the radium equivalent activity concentration for each city. The values of the concentrations of the primordial radionuclides varied widely within each city and among the cities. The weighted means for the cities range between 13.3 and 18.4, 28.2 and 71.6, and 176.2 and 336.8 Bq/kg for (226)Ra, (232)Th and (40)K, respectively. The city weighted means of radium equivalent activity concentrations for the eight cities range from 81 to 145 with a mean of 101 Bq/kg. The maximum for external hazard index was determined as 0.39. All the values are within the safety limits recommended by UNSCEAR [United Nations Scientific Committee on the Effects of Atomic Radiation 1982. Report to the General Assembly, with annexes. New York, United Nations.].