Abstract
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.
Highlights
For most human activities involving minerals and raw materials, the levels of exposure to these radionuclides are not significantly greater than normal background levels, and when these raw materials with low concentrations of naturally occurring radioactive materials (NORM) are introduced in an industrial process, the radionuclides can become more concentrated in the produced by-products or in waste material such as red mud in bauxite mining [3,4]
An Electret Ionization Chambers (EIC) for monitoring radon consists of a stable electret mounted inside an electrically conducting chamber
It has been proven that elevated radon concentrations indoors depend on several factors such as the building material, radon exhalation rate from the ground and house ventilation rate [25,26,27,28]
Summary
For most human activities involving minerals and raw materials, the levels of exposure to these radionuclides are not significantly greater than normal background levels, and when these raw materials with low concentrations of NORM are introduced in an industrial process, the radionuclides can become more concentrated in the produced by-products or in waste material such as red mud in bauxite mining [3,4] Such activities significantly increase the exposure of workers and the general public, meaning that they may need to be controlled by regulation in order to ensure the protection from radiation of relevant people. The limitations of EPERM detectors compared to RADTRAK detectors are discussed
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