R isk Assessment of Resident Farmer s in Kilimambogo , Kenya , Using RESRAD Computer Code.
Abstract
The concentration of radionuclides in the any given place is determined by the geology of the area. The levels of primordial radi-onuclides present in soil samples harvested from Kilimambogo region in Kenya was measured using a Thallium activated Sodium Iodide, NaI (TI) gamma spectrometry technique. RESRAD computer code was used to evaluate and model the dose exposure and the cancer risks for the residential farmer from the RESidual RADioactive materials for up to 1000 years. The mean activity con-centration of 226Ra, 232Th and 40K in soil samples were found to be 46 ± 6 Bq kg-1, 57 ± 6 Bq kg-1 and 603 ± 46 Bq kg-1 The total maximum received dose by the resident farmer was projected to be 3.477mSv y-1 at t= 470.9 years for all nuclides summed and all component pathways, with 226Ra, 232Th and 40K contributing maximum doses of 5.026 × 10-6 mSv y-1, 2.919 mSv y-1 and 0.558 mSv y-1 respectively. This was more than three-fold higher than the recommended dose limit of 1 mSv y-1 proposed by the International Commission on Radiological Protection (ICRP), and more than ten-fold dose limit of 0.25 mSv y-1 recommended in the RESRAD Code for members of the general public. The highest cancer risk from all the pathways was projected to be 7.583 × 10-3 at t = 30 years and the least, 4.558 × 10-3 at t=1000 years. Inhalation of radon and the decay products were projected to contribute the highest cancer risk of 3.306 × 10-3 at t= 0 years making radon the highest contributor to cancer risk.
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