Determination of Natural Radioactivity Levels and Potential Hazards of Limestone from Kyuso SubCounty, Kenya

Wycliffe M Mwendwa, Martin M Riara, Dorah Muthee, and Fidelis Ngugi
2026-11-12 1 views 0 downloads

 

Limestone, a major raw material for Portland cement production, may contain naturally occurring radionuclides with potential environmental and health implications. This study assessed the radiological characteristics of limestone from Kyuso Sub-County, Kenya, where mines are being explored as alternative sources because of the decline in supplies from existing mines. Fifty limestone samples were randomly collected, dried, crushed, homogenised, sieved, weighed, sealed, and stored for 30 days before analysis. The activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K were determined using a NaI(Tl) gamma-ray spectrometer, and associated radiological hazard indices were evaluated. The activity concentrations ranged from 16 ± 0.71 to 118 ± 4.58 Bq kg⁻¹ for ²³⁸U, 12 ± 0.52 to 88 ± 3.40 Bq kg⁻¹ for ²³²Th, and 199 ± 8.31 to 1468 ± 56.80 Bq kg⁻¹ for ⁴⁰K, with respective means of 37.24 ± 2.54, 42.31 ± 3.24 and 634.62 ± 37.07 Bq kg⁻¹. The mean ²³⁸U and ⁴⁰K concentrations exceeded their worldwide averages of 33 and 420 Bq kg⁻¹, respectively, while ²³²Th was below its worldwide average of 45 Bq kg⁻¹. The mean absorbed dose rate, radium equivalent activity, indoor and outdoor annual effective doses, external hazard index and internal hazard index were 71.20 ± 3.15 nGy h⁻¹, 146.30 ± 6.45 Bq kg⁻¹, 0.27 ± 0.011 mSv y⁻¹, 0.18 ± 0.007 mSv y⁻¹, 0.4 ± 0.017 and 0.5 ± 0.020, respectively. Although the absorbed dose rate and outdoor annual effective dose slightly exceeded their worldwide averages, the other indices were below the commonly used screening criteria. Overall, the results indicate no significant radiological concern under the assessment criteria applied. Further studies of radon and thoron exhalation and the final cement product are recommended.

 

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