Cosmic-ray exposure assessment using particle and heavy ion transport code system: case study Douala-Cameroon.

According to UNSCEAR, cosmic radiation contributes to ~16% (0.39 mSv/y) of the total dose received by the public at sea level. The exposure to cosmic rays at a specific location is therefore a non-negligible parameter that contributes to the assessment of the overall public exposure to radiation. In this study, simulations were conducted with the Particle and Heavy Ion Transport code System, a Monte Carlo code, to determine the fluxes and effective dose due to cosmic rays received by the population of Douala. In minimum solar activity, the total effective dose considering the contribution of neutron, muon+, muon-, electron, positron and photon, was found to be 0.31 ± 0.02 mSv/y at the ground level. For maximum solar activity, it was found to be 0.27 ± 0.02 mSv/y at ground level. During maximum solar activity, galactic cosmic rays are reduced by solar flares and winds, resulting in an increase in the solar cosmic-ray component and a decrease in the galactic cosmic-ray component on Earth. This ultimately leads to a decrease in the total cosmic radiation on Earth. These results were found to be smaller than the UNSCEAR values, thus suggesting a good estimation for the population of Douala city located near the equatorial line. In fact, the cosmic radiation is more deflected at the equator than near the pole. Muons+ were found to be the main contributors to human exposure to cosmic radiation at ground level, with ~38% of the total effective dose due to cosmic exposure. However, electrons and positrons were found to be the less contributors to cosmic radiation exposure. As regards the obtained results, the population of Douala is not significantly exposed to cosmic radiation.

Soil gas radon, indoor radon and its diurnal variation in the northern region of Cameroon.

Soil gas radon and indoor radon measurements have been carried out in Mayo-Louti and Benoué Divisions in northern Cameroon. Concentrations of radon in soil have been measured using Markus 10 at the depth of about 1 m. Radon concentration in soil varies from 0.9 to 13.8 kBq m-3 with a mean value of 4.6 kBq m-3. Average daily indoor radon concentrations measured with RadonEye+2 detectors vary from 7 to 60 Bq m-3 with an average of 17 Bq m-3. Indoor radon concentrations measured with passive RADTRAK detectors range between 15 and 104 Bq m-3 with a geometric value of 38 Bq m-3 and a geometric standard deviation of 1.5. This geometric value is lower than the value of 30 Bq m-3 given by UNSCEAR. Indoor radon inhalation dose ranges between 0.28 and 1.97 mSv a-1 with geometric value of 0.72 mSv a-1 (at 0.03 standard deviation). Outdoor radon inhalation ranges between 0.02 and 0.26 mSv a-1 with a mean value of 0.09 mSv a-1. The total annual effective dose due to indoor and outdoor radon exposure for this study area is 0.81 mSv a-1, less than 1.15 mSv a-1 the world average value given by UNSCEAR. There is no significant radiological risk for the inhabitants.

NATURAL RADIATION EXPOSURE TO THE PUBLIC IN MINING AND ORE BEARING REGIONS OF CAMEROON.

Within the framework of a joint research project on natural radiation exposure and its health effects in Cameroon from 2014 to 2017, the Institute of Geological and Mining Research and the Hirosaki University worked together to carry out natural radiation survey in mining and ore bearing regions of Cameroon. Air kerma rates were measured using car-borne survey method. In-situ gamma spectrometry was used to determine activity concentrations of 238U, 232Th and 40K in soil. A total of 450 RADUET detectors and 350 thoron progeny monitors were deployed in dwellings of the study areas for 2-3 months, collected and analysed. Although natural radioactivity level seems to be normal in most of the surveyed areas, there are many points where activity concentrations of natural radionuclides are largely above the world average values. Indoor radon, thoron and thoron progeny results show the importance to put in place the national radon plan in Cameroon. It was also pointed out that thoron cannot be neglected when assessing inhalation dose.