Screening measurement of indoor radon-222 concentrations by gamma-ray spectromentry in Kenyatta University
Chege, Margaret Wairimu
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Rn-222 and its progeny are the largest contributors to the total effective dose received by the general public. It is therefore of great concern to monitor radon concentration in dwellings. Measurements of indoor 222Rn concentrations in modern and traditional buildings were carried out for comparison purposes. The measurements were carried out in the Kenyatta University campus in Nairobi, Kenya, where modern buildings and a number of model traditional buildings co-exit. Charcoal canisters were employed to sample 222Rn by exposing the activated canisters at the sampling sites for 48 hours. After exposure, gamma emissions from 222Rn daughters trapped in the canister were analysed using Nal(TI) detector, and the 222Rn concentrations at the sampling sites were calculated. The average 222Rn concentration during the sampling period was 188 Bq/m3. 222Rn concentration varied from 30.2 to 315.4 Bq/m3 in the traditional houses and from 115.76 to 257.2 Bq/m3 in modern buildings. The average 222Rn concentration was higher in the modern building than in the traditional ones. The contribution of building materials as sources of indoor 222Rn was also investigated. This involved gamma spectrometric analysis of samples of building materials to determine their 226Ra concentration, using HPGe detector. The activity concentration of 226Ra ranged from 11.66-101.93 Bq/m3 with the highest value found in the mud used in the construction of the model traditional houses. The ranges of 40K and 232Th in the samples are 254.46-1246.79 Bq/m3 and 15.3 to 148.34 Bq/m3, respectively. The bulk exhalation rates of 222Rn from selected building materials were evaluated by enclosing samples in a 222Rn free can and monitoring 222Rn accumulation with time. 222Rn a exhalation rate was highest in the mud samples and lowest in stone and concrete samples.