NATURAL RADIATION EXPOSURE AND RADIOLOGICAL HAZARD ANALYSIS IN A RADON-PRONE AREA OF THE ADAMAWA REGION, CAMEROON

Passive and active indoor radon measurements were carried out in 127 dwellings in Ngaoundere city and three other localities in the Adamawa region, using alpha track detectors (RADTRAK(2)(R)) and RadonEyePlus2 detectors, respectively. Moreover, gamma ray spectrometry with NaI (Tl) detector was used to determine the activity concentrations of Ra-226, Th-232 and K-40 in 35 soil samples taken from the study areas. The RESRAD-Build computer code was used to assess the external effective dose resulting from the long-term exposure due to natural radionuclides. Indoor radon concentrations vary from 27 +/- 24 to 538 +/- 80 Bq m(-3) throughout the study area. In the locality of Ngaoundere, 100% of dwellings exceed 100 Bq m(-3), and 28% of them exceed 300 Bq m(-3). The daily maximum value of 697 Bq m(-3) was observed overnight and the minimum value of 106 Bq m(-3) during the afternoon. The average value of the inhalation dose was found to be 2.6 mSv y(-1) for the whole study area, and 5.6 mSv y(-1) for Ngaoundere city, higher than the world average value of 1.2 mSv y(-1). The comparison between in situ and laboratory measurements, and the RESRAD Build data of the external effective dose assessment did not show any significant difference. Based on the above results, Ngaoundere city can be classified as a high radon-prone area.