The current work deals with indoor radon (²²²Rn) concentrations and ambient dose-equivalent rate measurements in the bauxite-bearing areas of the Adamawa region in Cameroon before mining from 2022. In total, 90 Electret Ionization Chambers (EIC) (commercially, EPERM) and 175 Radon Track Detectors (commercially, RADTRAK²) were used to measure ²²²Rn concentrations in dwellings of four localities of the above region. A pocket survey meter (RadEye PRD-ER, Thermo Scientific, Waltham, MA, USA) was used for the ambient dose-equivalent rate measurements. These measurements were followed by calculations of annual doses from inhalation and external exposure. ²²²Rn concentrations were found to vary between 36 ± 8–687 ± 35 Bq m⁻³ with a geometric mean (GM) of 175 ± 16 Bq m⁻³ and 43 ± 12–270 ± 40 Bq m⁻³ with a geometric mean of 101 ± 21 Bq m⁻³ by using EPERM and RADTRAK, respectively. According to RADTRAK data, 51% of dwellings have radon concentrations above the reference level of 100 Bq m⁻³ recommended by the World Health Organization (WHO). The ambient dose equivalent rate ranged between 0.04–0.17 µSv h⁻¹ with the average value of 0.08 µSv h⁻¹. The inhalation dose and annual external effective dose to the public were assessed and found to vary between 0.8–5 mSv with an average value of 2 mSv and 0.3–1.8 mSv with an average value of 0.7 mSv, respectively. Most of the average values in terms of concentration and radiation dose were found to be above the corresponding world averages given by the United Nations Scientific Commission on the Effects of Atomic Radiation (UNSCEAR). Even though the current exposure of members of the public to natural radiation is not critical, the situation could change abruptly when mining starts.

In this study, a low-cost local device based on an Unmanned Aerial Vehicle (UAV) for real-time environmental radiation monitoring is proposed. The device consists of a Geiger-Müller ZP 1200 counter for gamma radiation detection and an appropriate electronic circuit for processing and shaping the detected pulses. The Geiger-Müller detector used is low-cost, insensitive to environmental temperature variations, and can be operated continuously over a long period. Two different methods were performed to calibrate the designed device, namely the use of a programmable nuclear pulse generator for electronic calibration and a Cs-137 gamma-ray calibration source. A long flight time UAV is developed locally with suitable characteristics and adapted to carry the radiation detection device. The designed UAV mainly consists of a multi-flight controller having an intelligent switching system associated with a GPS Module for accurate position-keeping and four heavy lift motors. The use of UAVs has the advantage that it allows measurements to be taken over large areas, even those that are difficult to access, and avoids exposing people to radiation. The flight measurement tests were carried out in the urban area of Yaoundé-Cameroon, at an altitude of 15 to 100 meters with a sweeping speed of about 20 km/h for 36 days from January 01, 2023, to February 06, 2023. The tests showed that the concentrations collected varied between 0.00697 μSv/h and 0.8706 μSv/h, of which 85.71% of data have a concentration below the threshold (0.3 μSv/h) and 14.29% above this threshold. These tests confirm that the developed radiation detection system works properly and is suitable for environmental radiation protection and nuclear safety activities.

This paper assesses public exposure to natural radioactivity from radon and external radiation sources in the Far North region, Cameroon, and studies the correlation between radon data obtained using several techniques. The RADTRAK, RadonEye, and Markus 10 detectors were used to measure radon concentrations in dwellings and soil, respectively. To understand radon variations in the study area, a correlation coefficient between radon in soil and in dwellings was determined. The ambient equivalent dose rate was measured using a RadEye PRD-ER, and the effective doses from internal and external radiation were determined. In soil, 20% of the measuring points had a concentration above 50 kBq m⁻³, the action value for radon exposure from soil according to Swedish Radiation Protection Institute regulations. After 90 d of measurement using RADTRAK, half of the concentrations in the dwellings were greater than or equal to 160 Bq m⁻³, which is above the WHO reference level of 100 Bq m⁻³. The ambient equivalent dose rate and the external and internal radiation effective dose were 0.08 μSv h⁻¹, 0.6 mSv y⁻¹, and 2.86 mSv y⁻¹, respectively. These results reveal a strong correlation between the radioactivity level of a locality and its geological and mineralogical structure. Although these different results in general do not present a very high risk of radiological exposure for the public, it is nevertheless necessary that the rules of radiation protection are respected in order to reduce it.

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.

The aim of the current work is to study the correlation between ²²²Rn gas in soil and indoor ²²²Rn concentrations. Markus 10 and RADTRAK detectors were used to measure ²²²Rn concentrations at 1 m depth in soil 30 points and 50 dwellings respectively. These concentrations varied from 35 kBq m⁻³ to 255 kBq m⁻³ with a geometric mean of 67 (18) kBq m⁻³, and from 85 Bq m⁻³ to 410 Bq m⁻³, with a geometric mean of 152 (26) Bq m⁻³ respectively in the soil gas and dwellings. In additional, 99% of the measurement points had concentrations higher than the limit value of 40 kBq m⁻³ according to the Swedish criterion for risk levels; 94% of the houses had radon concentrations higher than 100 Bq m⁻³, the reference value of the World Health Organization (WHO). When there was not a good air flow between the outside and the inside of the dwelling, the correlation coefficients were R² = 0.82 and R² = 0.73 respectively for the earthen and concrete dwellings. Under the best natural ventilation conditions, these correlation coefficients decrease significantly. Their values were R² = 0.54 and R² = 0.34 respectively for the earthen and concrete dwellings. Furthermore, a RadonEye +2 detector revealed a daily ²²²Rn accumulation reaching values of 800 Bq m⁻³ in some dwellings when all doors and windows were closed. Architecturally, dwellings built with sealed materials such as cement and concrete, whose do not facilitate ²²²Rn diffusion and transport, have lower ²²²Rn concentrations and effective dose than others These results show that ²²²Rn gas in soil and in confined air in dwellings are strongly correlated.