Gamma activity and radiation dose in concrete building blocks used for construction of dwellings in Jos, Nigeria.

Radioactivity concentrations of concrete building block samples made and used in Jos, Nigeria, were determined using a gamma ray spectrometry method. The mean values of the radioactivity concentrations were calculated as 66, 126 and 589 Bq kg(-1) for (226)Ra, (232)Th and (40)K, respectively. The radium equivalent activities ranged between 131 and 712 Bq kg(-1), with six of the samples exceeding the UNSCEAR reported maximum permissible level of 370 Bq kg(-1). The mean radium equivalent activity (292 Bq kg(-1)) is higher than the values available in the literature for some countries by factors ranging between 2 and 5, a situation that can be traced to the practice of sourcing sand aggregates from mining sites. The indoor annual effective dose for a dwelling of dimension 3.6 x 3.6 x 3.0 m(3) was calculated as 0.81 mSv.