NATURALLY OCCURRING RADIONUCLIDES IN SOIL SAMPLES OF BURETI SUB-COUNTY OF KERICHO COUNTY KENYA.

The activity concentration of soil samples of Bureti sub-county was measured using thallium-activated sodium iodide detector. To ascertain the level of radiation hazard to the public, gamma radiation dose rates were also estimated. The average activity concentration due to 40K, 226Ra and 232Th for soil samples are 1164 ± 70, 106 ± 8 and 79 ± 5 Bqkg-1, respectively. An average dose rate of 145 ± 10 nGyh-1 was recorded, which is about 2.5 times higher than the world average value of 60 nGyh-1(UNSCEAR). On the other hand, an average outdoor effective dose of 0.35 ± 0.02 mSvy-1 was measured, which is lower than the ICRP safety limit of 1 mSvy-1. This shows that the radiation hazards from naturally occurring terrestrial radionuclides in Bureti is low and therefore human radiation exposure is within the accepted limits.

ANNUAL EFFECTIVE DOSE ASSESSMENT DUE TO RADON AND THORON PROGENIES IN DWELLINGS OF KILIMAMBOGO, KENYA.

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.

Analysis of internal exposure associated with consumption of crops and groundwater from the high background radiation area of Mrima Hill, Kenya.

Specific concentrations of (226)Ra, (232)Th and (40)K were measured in cassava tubers, cassava leaves and groundwater obtained from the high background radiation area of Mrima hill and used in the evaluation of the ingested dose. Cassava tubers, cassava leaves and groundwater registered average (226)Ra concentrations of 60 ± 5, 141 ± 11 and 4.3 ± 0.3 Bq kg(-1), respectively. (232)Th was not detected in cassava leaves although it was present in cassava tubers as well as in groundwater in average concentrations of 35.3±61.5 and 2.0±0.1 Bq kg(-1), respectively. (40)K was present in all samples in average concentrations of 842±539 Bq kg(-1) in cassava tubers, 1708 ± 552 Bq kg(-1) in cassava leaves and 91.4 Bq kg(-1) in groundwater. The total annual effective dose due to ingestion was found to be 7.9 mSv y(-1) of which 2.4 mSv y(-1) was due to cassava tubers, 3.8 mSv y(-1) due to cassava leaves and 1.7 mSv y(-1) due to water.

Estimation of annual effective dose due to radon and thoron concentrations in mud dwellings of Mrima Hill, Kenya.

This study presents radon and thoron concentration measurements and the corresponding effective dose rates in mud dwellings located in the high background radiation area of Mrima Hill, Kenya. Discriminative technique was used for simultaneous measurement of radon and thoron. The effective dose was evaluated based on the concentration of the isotopes and the time spent indoors. Radon concentration ranged from 16 to 56 Bq m(-3) with an average of 35±14 Bq m(-3) and a corresponding annual effective dose of 0.67 mSv y(-1), while that of thoron ranged from 132 to 1295 Bq m(-3) with an average of 652±397 Bq m(-3) and an effective dose of 13.7 mSv y(-1).

The influence of meteorological parameters on indoor radon in selected traditional Kenyan dwellings.

The effects of outdoor temperature, rainfall and wind speed on the indoor radon concentration in four types of traditional hut in Kenya were investigated by performing short-term (about 48 h) measurements with activated charcoal canisters. The concentrations vary widely (30.2-315.4 Bq m(-3)) during the study period, and the overall mean is 170.3 +/- 39.6 Bq m(-3). The indoor radon concentration correlates negatively with both the outdoor temperature (R(2) = 0.06) and the wind speed (R(2) = 0.11) but positively with rainfall (R(2) = 0.03). The results showed that changes in meteorological parameters cause more variations in indoor radon concentrations than the differences in the buildings' characteristics (i.e., designs, materials, etc). However, these variations are not significant (at 1% significance level).