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222Rn and 220Rn surface exhalation rates from earthen building materials used in high background radiation areas of Homa and Ruri, Kenya have been measured using an accumulation chamber coupled with RAD7 detector. Activity concentrations of 226Ra and 232Th in the building materials were determined by γ-ray spectroscopy. In Homa the average 222Rn surface exhalation was 1 ± 0.1 mBqm-2 s-1, while that of 220Rn was 18 ± 2 Bqm-2 s-1; in Ruri 222Rn was 0.9 ± 0.1 mBqm-2 s-1 and 220Rn was 25 ± 3 Bqm-2 s-1. 222Rn was 26 times lower than world average and 220Rn was higher by a factor of 21. Average 232Th in Ruri was 1094 ± 55 Bq/kg, three times that in Homa; 226Ra was 129 ± 10 and 111 ± 6 Bq/kg in Homa and Ruri, respectively. There was a strong correlation between exhalation rate of 222Rn and concentration of 226Ra, as well as between 232Th and 220Rn. Thus, 220Rn was the major contributor to the inhaled dose in earthen dwellings of the two regions., (© The Author(s) 2021. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The activity concentration of radon in underground water of Bureti sub-county was measured using liquid scintillating counter device. The average radon activity concentration in all the water samples was 12.41 Bql-1. The maximum and minimum activity concentrations of radon were 22.5 and 4.57 Bql-1, respectively. In total, 53% of the total samples analysed had radon concentration levels above the US Environmental Protection Agency-recommended limit of 11.1 Bql-1. The annual dose received by an individual as a result of waterborne radon was determined according to the United Nations Scientific Committee on the Effect of Atomic Radiation reports and was found to be 33.23 𝜇Svy-1. All the samples recorded a value <100 𝜇Svy-1 recommended by the World Health Organization and the European Union council., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Six research studies involving radon and thoron in Kenya were carried out between 1997 and 2007. The studies were mainly small scale and involved a few areas scattered across Nairobi, Rift Valley, Coast and Western regions. The results were captured in seven online journal articles. This paper relooks at the journal articles with the view of underscoring the high radon and thoron areas in Kenya, raising awareness on the sources and risks of radon isotopes in indoor environments and highlighting the need for more research on the isotopes in the country., (© The Author(s) 2019. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Human beings are continuously exposed to ionising radiation originating from natural or artificial sources. Uranium-238 and Thorium-232 found in building materials are important sources of radon and thoron in the indoor environment. The concentration levels of radon, thoron and thoron progeny were measured in mud-walled, metallic or iron sheet-walled and stone-walled modern houses in Kilimambogo region, Kenya for 3 months. Radon and thoron concentration levels were measured using passive radon-thoron discriminative monitors (RADUET), while thoron progeny concentrations as the equilibrium equivalent thoron concentration (EETC) were measured using thoron progeny monitors. The mean radon concentration levels in mud, metallic and stone-walled dwellings were 67 ± 11, 60 ± 10 and 75 ± 10 Bq m-3, respectively. The mean thoron concentration levels in the corresponding dwellings were 195 ± 36, 71 ± 24 and 161 ± 31 Bq m-3, respectively, while EETCs were 12 ± 2, 3 ± 1 and 7 ± 1 Bq m-3, respectively. The annual effective doses for radon were 1.3 ± 0.2, 1.1 ± 0.1 and 1.4 ± 0.2 mSv y-1 in mud, metallic and stone-walled houses while those from thoron estimated from EETC were 2.4 ± 0.4, 0.5 ± 0.1 and 1.5 ± 0.2 mSv y-1 in the corresponding houses, respectively., (© The Author(s) 2019. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)