Radiological analysis of construction stones from selected quarries in Machakos County - Kenya

Abstract

All living organisms continuously are exposed to radiations of natural origin which originates from comics, terrestrial (soils and rocks) and radon. This work presents the radiological studies of sample rocks in Machakos County in Kenya which her basement systems are highly dominated by Metamorphic and Igneous rocks. The radiometric analysis of rock samples from Kyasioni, Mavoloni and Kathaana quarries would provide necessary radiological data to the community. To ascertain the radiological levels of different radionuclides from quarry rocks, a total of forty-two rock samples were randomly collected from the three quarry sites. These samples were independently prepared for activity concentration measurements which was later done by use of NaI(Ti) detector. The results obtained from analysis shows that, the average activity concentration for 238U, 232Th and 40K was 74.75 ± 3.15 Bq/Kg, 118.48 ± 1.91 Bq/Kg and 1120.35 ± 30.07 Bq/Kg from Kyasioni quarry, 63.25 ± 3.08 Bq/Kg, 81.82 ± 1.62 Bq/Kg and 1112.55 ± 30.97 Bq/Kg from Kathaana quarry while Mavoloni quarry site values were 67.00 ± 3.09 Bq/Kg, 105.52 ± 1.97 Bq/Kg and 1019.17 ± 29.79 Bq/Kg respectively. These activity concentration values, though higher than the recommended limits did not pose major radiological threat to the population because their associated radiological parameters were within management levels. The absorbed dose rate in air was 156.94 ± 3.98 nGy/hr, 126.4 ± 3.72 nGy/hr and 140.67 ± 3.99 nGy/hr from Kyasioni, Kathaana and Mavoloni quarries respectively, against a set limit of 60 nGy/hr. Additionally, the internal radiation hazard index from Kyasioni and Mavoloni quarry surpassed the set limit of unity by 0.13 and 0.01 respectively while all the other parameters were within the set limits. Kyasioni quarry reported the highest radium equivalent activity of 326.77 ± 8.37 Bq/Kg while Kathaana recorded the lowest value of 260.44 ± 7.77 Bq/Kg. The same trend was witnessed for outdoor and indoor annual effective dose (AEDR) with Kyasioni quarry reporting the highest indoor AEDR of 0.58 mSv/y while Kathaana quarry had the lowest value of 0.47 mS/y. Besides the higher activity levels for the three radionuclides, only two radiological parameter limits (absorbed dose rate and internal hazard index) were surpassed and hence the buildings materials from these quarries are radiologically safe for construction purposes.