RADIATION EXPOSURE LEVELS ASSOCIATED WITH GOLD MINING IN SAKWA WAGUSU AREA, BONDO DISTRICT, KENYA.

2Aguko W.O., 1Kinyua R., and 2Ongeri R.M. 1Institute of Energy and Environmental Technology, Jomo Kenyatta University of Agriculture and Technology, Nairobi-Kenya. 2&2Physics Department,
Jomo Kenyatta University of Agriculture and Technology, Nairobi-Kenya.
E-mail: masira_j@yahoo.com
ABSTRACT
The concentrations and distribution of natural radionuclides in soils and water from around Sakwa Wagusu Area, Kenya were investigated with an aim of evaluating the environmental radioactivity and radiological health hazard. These radionuclides are a source of radiation exposure which has been documented to have detrimental health effects for populations living in high background radiation area. Thirty nine rock and soil samples were collected from ten sites of Sakwa Wagusu area, Bondo district to measure their natural radioactivity concentrations due to 226Ra, 232Th and 40K radionuclides. Measurements were done by use of gamma spectrometry method with a high purity germanium (HPGe) detector. The calculated activities for 226Ra ranged from 7.2 – 113.8 Bqkg-1 (mean: 44.2Bqkg-1), for 232Th ranged from 4.6 – 100.7 Bqkg-1(mean: 40.3Bqkg-1) and for 40K ranged from 119.3 – 1611.8Bqkg-1 (mean: 639.6Bqkg-1). The mean measured absorbed dose rate for the areas under study, measured at 1m above the surface was 141.6nGyh-1 while the calculated total absorbed dose rates were found to average 69.8nGyh-1 below the surface. To evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity, the external hazard index, internal hazard index, the absorbed dose rate and the effective dose rate have been calculated and compared with internationallyapproved values. The radium equivalent activity values of all samples are lower than the limit of 370Bqkg-1. The values of the external and internal indices are less than unity. The calculated mean outdoor effective dose rate was 0.17mSvy-1 and is less than 1mSvy-1 upper limit recommended for the public by ICRP. An excess lifetime cancer risk of 0.02% was achieved with an assumption of 30% occupancy factor, the risk factor of 0.04 per Sv (ICRP, 2008) and the mean annual effective dose rate of 0.17mSvy-1.