Air absorbed dose rate measurements and external dose assessment by car-borne survey in the gold mining areas of Betare-Oya, Eastern-Cameroon

In order to assess radiological exposure of the public due to natural occurring radioactive materials from gold mining areas of Betare-Oya and vicinity, Eastern Cameroon, a preliminary study was carried out in 2015 for laboratory measurements of activity concentrations of primordial radionuclides. In terms of annual effective dose, results revealed a mean value of 0.34 mSv y^-1. However, it was necessary to make air absorbed dose rate contour map for a detailed evaluation of external dose. For this purpose, a car-borne survey using a 3-in × 3-in NaI(Tl) scintillation spectrometer was carried out in Betare-Oya and vicinity. Absorbed dose rates in air ranged from 23 to 80 nGy h^-1 with a mean value of 44 ± 7 nGy h^-1. The average values of activity concentrations in soil of ⁴⁰K, ²³⁸U and ²³²Th were 197 ± 21 Bq kg^-1, 37 ± 13 Bq kg^-1 and 32 ± 7 Bq kg^-1 respectively. ²³²Th was found to be the main contributor to the absorbed dose rate in air from outdoor terrestrial radiation in the study areas with a mean value of 43%. External annual effective dose ranged from 0.17 to 0.60 mSv y^-1 with a mean value of 0.33 ± 0.05 mSv y^-1, in agreement with the result (0.34 mSv y^-1) of the previous study performed in the same areas using gamma spectrometry in laboratory for radioactivity measurements in soil samples. This survey first and widely revealed an aspect of natural radiation exposures in soil mining areas of Eastern Cameroon. (author)