Abstract
In this paper, documented studies on radon and thoron concentrations in earthen dwellings and 238U and 232Th concentrations in soil in Kenya are reviewed. High concentrations of the isotopes were recorded in the earthen dwellings despite being generally well ventilated. Mrima Hill in the Coast region recorded the highest thoron levels with a mean of 652 Bq m−3. Twenty five percent of dwellings had thoron concentration in excess of 1,000 Bq m−3. Notably high indoor radon levels were recorded in Taita Taveta also in the Coast region, and in Kenyatta University situated in Nairobi in the Central region of the country. Radon concentration in the Rift Valley region was found to be too low to contribute significantly to radiation exposure. Based on studies on the concentration of 238U and 232Th in soil, the Southwestern region of the country was anticipated to have elevated radon/thoron concentrations in earthen dwellings. Existing studies involving measurement of indoor radon and thoron, and 226Ra and 232Th in soil are relatively few and of a small scale. More extensive studies are therefore necessary not only to corroborate the risk projections but to also generate sufficient data to enable countrywide mapping of indoor radon/thoron risk-prone areas.
Highlights
Radon and thoron gases can become airborne under favorable conditions and accumulate in confined spaces such as dwellings becoming significant sources of internal radiation exposure [1]
This is because the risk resulting from radon/thoron exposure depends, among other factors, on the activity of the radionuclides and from a theoretical perspective, a considerably small fraction of thoron atoms is required to produce the same activity as radon atoms
In addition to radon, thoron is a potential source of radiation exposure in earthen dwellings typical to rural Kenya
Summary
Radon and thoron gases can become airborne under favorable conditions and accumulate in confined spaces such as dwellings becoming significant sources of internal radiation exposure [1]. The fraction that eventually becomes airborne is often considered too low to contribute significantly to radiation exposure This is because the risk resulting from radon/thoron exposure depends, among other factors, on the activity of the radionuclides and from a theoretical perspective, a considerably small fraction of thoron atoms is required to produce the same activity as radon atoms. As an example, it requires just 17 thoron atoms to produce the same activity as 100,000 radon atoms due to the different half-lives. According to UNSCEAR [3], the risk from thoron
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