Measurement of natural radioactivity and dose rate assessment of terrestrial gamma radiation in the soils of Karibib and Okahandja, Namibia

The activity concentrations of the naturally occurring radionuclides 238U, 232Th and 40K in soil samples taken from the towns of Okahandja and Karibib in Namibia have been determined by gamma-ray spectroscopy using an HPGe detector. The average activity concentrations of 238U, 232Th and 40K in Karibib are 29.4 ± 5.8Bq/kg, 49.0 ± 8.6Bq/kg, and 824.3 ± 153.5Bq/kg while they are 40.9 ± 8.6Bq/kg, 57.9 ± 19.4Bq/kg, and 562.4 ± 125.4Bq/kg respectively in Okahandja. Most of these values are much higher than the corresponding worldwide average values. These activity concentrations were used to calculate different radiological parameters in order to evaluate the associated health hazard. The value of 9.5 × 10−2 mSv/y obtained for the mean effective dose rate in both towns is far below the permissible limit of 1.0mSv/y recommended by the ICRP and implies that there is no significant radiation hazard in the towns. Also, the values of 163.0Bq/kg and 167.1Bq/kg obtained for the average radium equivalent activity (Raeq) in the towns and the corresponding values obtained for the average external hazard index (Hex) are much below their maximum permissible limits thus confirming that radiological hazard is negligible in the towns.