| dc.description.abstract | Natural radiation levels in Olkaria geothermal area have been assessed ad reported. The assessment focused on soil radioactivity and radon levels in water and indoor environments. Soil samples were drawn at random from various sites of the geothermal area. Water samples were drawn from the geothermal wells, springs, water treatment plants, geothermal cooling plant and taps. Indoor environments sampled were geothermal power station offices and residential houses located at about 1.5 kilometers from the power station herein called X2-housing camp.
Soil radioactivity has been assessed for natural radionuc1ides such as 4OK, 238U, 232Th and 22~a sub-series. The activity concentrations of these radionuc1ides have been measured using hyper-pure germanium spectrometer equipped with HPGe detector. The radon levels in water and indoor dwellings have been assessed using Electret Passive Environmental Radon Monitor (E-PERM1M) which involves electrets and an ionchamber. The two are collectively called Electret Ionization Chamber (EIC).
The mean activity concentrations obtained for 238U series, 232Th series, 226Ra sub-series and 40K are 73.7 ± 7.4, 149.3 ± 17.0, 163.8 ± 18.6 and 1095.2 ± 53.2 Bq kg' respectively. Radon e22Rn) activity concentrations measured in water range from 2.0 ± 0.4 to 8.6 ± 0.1 K Bq m-3 with an overall mean value of 5.6 ± 0.5 K Bq m-3. None of the categories of water source reported a value above 10K Bq m-3, the recommended radon concentration in water (UNSCEAR, 1993). More so, the overall mean concentration of 5.6 ± 0.5 K Bq m-3 is less than 11 K Bq m', the. permissible concentration of radon in water (US- EP A, 1993). For the indoor environments, 222Rn activity concentration range from 5.13 ± 0.70 to 83.47 ± 0.10 Bq m-3 with a mean value of 41.05 ± 3.20 Bq m'. The mean value falls far below the safety limit of 200 - 600 Bq m-3 (UNSCAER, 1993).
From the activity concentrations of the natural radionuclides in soils, water and indoor environment, the absorbed dose rate in air and corresponding annual effective dose have been computed. For the soil, the calculated total mean values of the two dosimetric quantities are 214 nGy h-I and 0.53 mSv il respectively. Compared with the corresponding world average values of 57 nGy h-I and 0.46 mSv il respectively, it can be concluded that the area investigated has high background radiation levels.
Similarly, total mean effective dose due to 222Rn activity in water has also been computed as 46.55 ± 10-3 mSv il assuming dose to adults only and water consumption rate of 0.5 liters per day.
Breaking the effective dose due radon into two components, the calculated effective dose due to radon gas only is 0.09 mSv il while that due to short-lived radon decay products dissolved in soft tissues is 1.87 mSv il. Both calculations have been made assuming equilibrium factor of 0.4. Taken together, the findings of the present study have shown that the geothermal area does have significant levels of background radiation which therefore calls for a need to initiate epidemiological investigation of the health implications that may arise from that.
The study has also reported some reasonable levels of radon both in water and indoor environments which supports the suggestion that radon can be used to explore geothermal activity in the area. Even though the levels of waterborne and indoor radon reported in this study are generally low, complacency is discouraged here because the health effects of radon are known to be long term. This study thus presents a good basis for further investigation of natural radiation levels in the geothermal area. | en_US |
