Radioactivity and Trace Elements in Rock/ Soil Samples and Dose Assessment of the Public Residing near Homa Mountain, Homa Bay County, Kenya

Abstract

The concentration and distribution of natural occurring radioactive materials (NORM) in rock and soil samples from Homa Mountain area located in southwestern Kenya were measured to evaluate the environmental radioactivity and dose resulting from exposure to NORM. The gamma dose rate levels were determined using hand held survey meters in situ. The average outdoor absorbed dose rate in air at 1 m above the ground was found to vary from 108.4 to 1596.4 nGy h-1. Rock and soil samples collected were analyzed in the laboratory using hyperpure Germanium (HpGe) detector to assess the concentrations of NORM. The average values of the radioactivity concentrations of 40 K, 226Ra and 232Th in the rock and soil samples were 915.6, 195.3 and 409.5 Bq kg-1, respectively. The highest values of 40K, 226Ra and 232Th concentrations (3017.8, 1567.5 and 1447.0 Bq kg-1, respectively) were from samples collected at Homa Mountain and Chiewo hill which are both being encroached with human habitations. Energy Dispersive X-ray fluorescence when used was able to identify up to 18 elements among them K, Th and U. Using the concentration data obtained in this study, the range of the annual effective dose for a person living in Homa Mountain area was calculated to vary from 28.6 to 1681.2, with a mean of 470.4 µSv. The measurements show that the rock and soil samples from Homa Mountain have elevated levels of natural radioactivity and therefore qualify the region as a high background radiation area. The implication is that local materials used for building and human settlements should be controlled by local authorities. Access to Instrumental Neutron Activation Analysis would enhance the sensitivity and number of trace elements that can be deduced. The presence of rare earth elements provides possibilities for commercial exploitation that may result in economic benefit for the County and Country.