TITLE:
Natural Radioactivity and Radiological Dose Assessment of Rocks from Mbeere South, Kenya
AUTHORS:
James Ndirangu Wambugu, William Ndeke, Martin Mutie
KEYWORDS:
Natural Radioactivity, Radium Equivalent, Absorbed Dose, Annual Effective Dose, Mbeere South
JOURNAL NAME:
Open Access Library Journal,
Vol.13 No.10,
October
16,
2026
ABSTRACT: Natural radioactivity in rocks and building materials is a major contributor to outdoor gamma radiation exposure. This study determined the activity concentrations of 238U (estimated via 226Ra assuming secular equilibrium), 232Th and 40K and assessed radiological hazard indices in 30 purposively sampled rocks from Mbeere South, Embu County, Kenya using high-resolution HPGe gamma-ray spectrometry. Mean activity concentrations were 19.02 ± 14.00 Bq∙kg−1, 38.66 ± 34.43 Bq∙kg−1 and 634.88 ± 302.94 Bq∙kg−1 for 238U, 232Th and 40K, respectively (40K > 232Th > 238U). 238U was below the world average of 35 Bq∙kg−1, while 232Th and 40K were 28.9% and 58.7% above world averages of 30 and 400 Bq∙kg−1. Mean radium equivalent activity (Raeq), absorbed dose rate (D) and outdoor annual effective dose (AEDout) were 123.19 ± 73.10 Bq∙kg−1, 58.61 ± 33.21 nGy∙h−1 and 0.0719 ± 0.0407 mSv∙y−1, respectively. All Raeq values were below the 370 Bq∙kg−1 screening limit, and mean D and AEDout were comparable to world averages of 59 nGy∙h−1 and 0.07 mSv∙y−1. These values were 53% - 91% lower than high-background areas in Kenya, Nigeria, Saudi Arabia and Brazil, and comparable to Jaintiapur, Bangladesh. The results indicate low external gamma hazard; suitability with respect to indoor radon was not assessed.