Assessment of Natural Radio Activity Concentration Levels in Geological Samples Collected In Selected Areas in Makueni County
Mutungi, Mutunga James
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Natural radiation is the major contributor to the external dose and varies depending on the radioactivity concentration of naturally occurring radionuclides and their decay products in soil and rocks. Exposure to a high dose to human beings leads to health problems. Assessment of natural radioactivity concentration levels in geological samples collected in selected areas of Makueni County was carried out using gamma ray spectroscopy technique. Spectrum decomposition method was used to decompose the measured gamma ray spectra into spectral components of separate radionuclides. The measured peak intensities were used to calculate the activity concentration of the radionuclides in the samples. The average concentrations of 238U, 232Th and 40K measured in the soil samples collected in this study were 69 + 5 BqKg-1,53 + 3 BqKg-1 and 1098 + 69 BqKg-1 respectively while rocks were found to have concentrations of 139 + 6 BqKg-1, 73 + 3 BqKg-1, 1573 + 65BqKg-1 respectively. On average both rocks and soils were found to have activity concentrations of 104 + 5 BqKg-1, 63 + 3 BqKg-1, 1336 + 67 BqKg-1 for 238U, 232Th and 40K respectively. These values are above the global average values. To measure radiation hazard to the public, absorbed dose rate in air at a height of 1m above the ground surface was estimated. Absorbed dose rate in rocks was 175 + 7 nGyh-1 while in soil it was found to be 110 + 7 nGyh-1 These values are higher than the world average of 60 nGyh-1 (UNSCEAR, 2002).The effective dose rate calculated for human exposure from the ionizing radiations of 238U,232Th and40K in the soil samples collected were found to have 0.29 + 0.02 mSvy-1 while rocks registered 0.45 + 0.02 mSvy-1 These health hazard parameters were below the safe limit of 1.0 mSvy-1 (ICRP, 1991; UNSCEAR, 2002) and therefore do not indicate significant health hazard for the inhabitants of the selected area. The building materials from the study area are safe for use and I recommend that the government and other non- governmental organizations use this study as a baseline study in radioactivity concentration levels of the area.