The level of natural radioactivity has been evaluated for soil samples collected from the uranium and thorium bearing region of Lolodorf in the southwestern Cameroon. Specific activities of 226 Ra, 232 Th and 40 K in these soil samples were determined using γ-ray spectrometry with sodium iodide (NaI(Tl)) detector. The specific activities for the whole study areas where consist of five inhabited localities were compared with the world average and permissible recommended limits. Specific activities of 226 Ra, 232 Th and 40 K ranged from 5-120, 2-170 and 50-253 Bq kg −1 , with average values of 22±2, 37±6 and 98±7 Bq kg −1 , respectively. The average values of absorbed dose rate in air (D a), external effective dose (E ext), radium equivalent activity (Ra eq), external hazard index (H ext) and representative level index (I γ) were 36.7±5.0 nGy h −1 , 0.29±0.04 mSv y −1 , 83±14 Bq kg −1 , 0.22±0.03 and 0.58±0.10 respectively, which, were lower than their recommended values. Although this study shows that radioactivity level is normal in the study areas, except some areas where the uranium and potassium anomalies had been found by previous investigations, the possibility of developing cancer cases among individuals must not be neglected. The soil from the sampling areas in this study can be used safely as building materials apart from some points within Ngombas and Kribi.
The present work was aimed at measuring indoor radon activity concentrations in dwellings in Mvangan locality, South Cameroon, in order to assess the extent of measures that may be necessary for controlling public indoor radon exposure in this area. Measurements were carried out using passive solid-state nuclear track detectors (RADONAVA Inc., RadTrak2, Sweden) following ISO 11665-4 standard. Radon concentration ranged between 36 ± 20 and 150 ± 30 Bq m−3 with arithmetic and geometric means values of 64 ± 25 and 60 ± 1 Bq m−3, respectively. These mean values were greater than worldwide values presented by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which are, respectively, 40 and 30 Bq m−3. 96% of dwellings that have radon concentrations below the World Health Organization (WHO) reference level of 100 Bq m−3, whereas 4% of dwellings have radon concentrations higher than this level but lower than 300 Bq m−3, the International Commission on Radiological Protection (ICRP) reference level. Annual effective doses due to indoor radon ranged between 0.7 and 2.8 mSv y−1 with an arithmetic mean value of 1.2 ± 0.5 mSv y−1. These values were below the lower limit of the ICRP-recommended action level interval 3–10 mSv y−1. It has been observed that annual effective dose received by residents in cement bricks dwellings were not significantly different (P-value = 0.565) than those received by residents in mud dwellings in Mvangan locality. The mean number of persons expected to be diagnosed with or die from cancer (solid cancers and leukemia) were 162 ± 48 (61 ± 25 for males and 101 ± 41 for females) and 82 ± 24 (33 ± 13 for males and 49 ± 20 for females), respectively. The results obtained in this study prove that the populations of Mvangan locality are exposed to a relatively low potential risk of cancer incidence and mortality.
The objective of the current study is to investigate natural radioactivity of some building materials, the resulting long-term external and internal effective dose equivalents (EEDE and IEDE) analysis followed by indoor radon measurements as well as the assessment of some radiological risk indicators associated with radon exposure. A total of 37 samples of building materials were analyzed with a sodium iodide detector (NaI (Tl)) and the computer code RESRAD-BUILD was used for the analysis of the EEDE and IEDE of the structural elements of the houses (walls and floor). For indoor radon measurements, 140 houses were selected and in each of them was placed 01 RADTRAK dosimeter. Inhalation dose, total dose and some radiological risk indicators were calculated. The specific activities of 226Ra, 232Th and 40K for the overall sampled building materials were found to vary between 10±2–52±7, 10±1–95±10 and 31±1– 673±20 Bq kg-1 respectively. The dwelling types with bare brick walls, cement mortar plastered walls and concrete floors show EEDE and IEDE values well below the recommended limits. The corresponding dwelling types contributions to the measured average indoor radon concentration (42±12 Bq m-3) are 22%, 13% and 16% respectively. Inhalation dose resulting from the measured indoor radon concentrations varies from 0.35 to 3.24 mSv y-1 with a mean value of 0.96±0.55 mSv y-1, which represents about 65% of the total dose simulated (1.49±0.88 mSv y-1) by the RESRAD-BUILD code. The overall analysis of indoor radon-related radiological risk indicators shows low levels of risk relative to permissible limits.
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