Natural radioactivity and radiological hazard analysis of construction stones from various quarries in Machakos County-Kenya

The radioactivity levels of rocks sampled from the quarries of Kyasioni, Mavoloni and Kathaana located in the lower Eastern County of Machakos in Kenya were determined. Forty-two samples were collected using stratified random sampling and analysed using NaI(TI) detector with a specially designed lead shield. The parametric values of activity concentration, absorbed dose, annual dose rate and hazard indices were estimated using activity-dose relations suggested in UNSCEAR and ICRP reports. The mean activity concentration for the entire work for U-238 (Ra-226), Th-232 and K-40 were 68.33 & PLUSMN; 3.11, 101.10 & PLUSMN; 1.83 and 1084.02 & PLUSMN; 30.28 Bq/kg, respectively. Kyasioni quarry presented the highest activity concentration of 74.75 & PLUSMN; 3.15, 118.48 & PLUSMN; 1.91 and 1120.35 & PLUSMN; 30.07 Bq/kg for Ra-226, Th-232 and K-40, respectively. The average annual effective dose was estimated as 0.58 & PLUSMN; 0.01, 0.47 & PLUSMN; 0.01 and 0.52 & PLUSMN; 0.01 mSv/y for Kyasioni, Kathaana and Mavoloni quarries, respectively. Other radiological parameters estimated from the corresponding activities were within the recommended limits hence guaranteeing safety to the users.