Assessment of natural radioactivity and associated radiation hazards in some Cameroonian building materials

The concentration of U-238, Th-232 and K-40 in 13 building materials obtained from factories and collected in field in Cameroon were investigated by gamma-ray spectrometry. The activity ranged from 1.76 to 49.84 Bq kg(-1), 0.32 to 147 Bq kg(-1) and 18 to 1226 Bq kg(-1) for U-238, Th-232 and K-40, respectively. The highest 238U activity was found in compressed red soil brick type I (49.6 +/- 0.3 Bq kg(-1)) produced by a local manufacturer while the highest Th-232 (139 +/- 13 Bq kg(-1)) and K-40 (1162 +/- 108 Bq kg(-1)) activities were found in gravel collected from an exploitation site in Logbadjeck. The activities are compared with available data from other investigations and with the world average value for soils. The radium equivalent activity Ra-eq, the external hazard index Hex, the indoor absorbed dose rate D in air and the annual effective dose equivalent E were evaluated to assess the radiation hazard for people living in dwellings made of the materials studied. All building materials have shown Raeq (range from 10 to 313 Bq kg(-1)) lower than the limit of 370 Bq kg(-1) set in the Organization for Economic Cooperation and Development [OECD, 1979. Exposure to radiation from the natural radioactivity in building materials. OECD, Paris] report which is equivalent to a gamma-dose of 1.5 mSv yr(-1). Except for the gravel from Logbadjeck, all the materials examined are acceptable for use as building materials as defined by the OECD criterio

Radioactivity level and soil radon measurement of a volcanic area in Cameroon

The radioactivity level of soils in a volcanic area in Cameroon was determined and discussed. Thirty soils samples were collected from Buea and Limbé cities located in the south-western Cameroon. These two regions are known for theirs volcanic grounds due to the presence of Mount Cameroon Mountain. The activity concentrations of natural radionuclides as well as that of the fission product were evaluated by gamma-ray spectrometry using a hyper-purity germanium detector (HPGe). The ranges of concentrations in the surveyed soils were 11–17 Bq kg−1, 22–36 Bq kg−1 and 43–201 Bq kg−1 for 226Ra, 232Th and 40K, respectively. The radioisotope 137Cs was also found but in a very small amount. The outdoor absorbed dose rate 1 m above ground with the corresponding annual effective dose rate, assuming a 20% occupancy factor was estimated. The radium equivalent and the external hazard index were also evaluated and results are compared with available data from other studies and with the world average value [United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), 1988. Sources, Effects and Risks of Ionizing Radiation. Report to the General Assembly on the Effects of Atomic Radiation. United Nations, New York; UNSCEAR, 2000. Sources and Effects of Ionizing Radiations. Report to the General Assembly with Scientific Annexes. United Nations, New York]. A solid state nuclear track detector (SSNTD), LR-115 was used for soil radon measurements at a depth of 50 cm. The ranges of soil radon concentrations were 6.7–10.8 kBq m−3 and 5.5–8.7 kBq m−3 in Buea and Limbé, respectively. A positive correlation was found between concentrations of radium measured with γ-spectrometry and the soil radon concentrations measured with the nitrate cellulose detectors. The results of this study provide the radioactivity level in soil of a volcanic area, which has been found to be within the safety limits. The south-western Cameroon can be considered as having normal natural background radiatio

226^{226}Ra, 232^{232}Th and 40^{40}K contents and radon exhalation rate from materials used for construction and decoration in Cameroon

This work deals with the measurement of radioactivity and radon exhalation rate from building materials manufactured in Douala city from geological materials. Nine types of building material were surveyed for their natural radioactivity contents using high-resolution gamma-ray spectrometry. The activity concentrations for Ra-226, Th-232 and K-40 varied from 11.5 to 49 Bq kg(-1), 16 to 37 Bq kg(-1) and 306 to 774 Bq kg(-1), respectively. The absorbed dose rate in the samples investigated at 1 m above ground level ranged from 28.5 to 66.6 nGy h(-1). External and internal hazard indices were also estimated as defined by the European Commission. The Ra equivalents of the materials studied ranged from 57.5 to 133 Bq kg(-1) and are much smaller than the recommended limit of 370 Bq kg(-1) for construction materials for dwellings. Polycarbonate nuclear track detectors (NTDs), type CR-39, were used for measuring the radon concentration from different materials. In fact, knowledge of the radon exhalation rate from building materials is important for understanding the individual contribution of each material to the total indoor radon exposure. Samples were hermetically closed in glass vessels and the radon growth was followed as a function of time. The radon exhalation rate was therefore derived from the experimental measurement of a-track densities. The radon exhalation varied from (5.77 +/- 0.06) x 10(-5) to (7.61 +/- 0.07) x 10(-5) Bq cm(-2) h(-1) in bricks, from (5.79 +/- 0.05) x 10(-5) to (11.6 +/- 0.12) x 10(-5) in tiles, and was (6.95 +/- 0.03) x 10(-5) Bq cm(-2) h(-1) in concrete. A correlation (correlation coefficient similar or equal to 0.8) was found between radium concentration measured with a HPGe detector and the radon exhalation rate obtained using nuclear track detector