Spatial Variation of Natural Gamma Radiation and Radiological Dose around a University Hostel Environment in Zaria, Nigeria

Abstract

Natural radioactivity from terrestrial radionuclides significantly raises ambient radiation exposure in densely populated regions and must be routinely monitored. This study assessed the geographical distribution and radiological consequences of natural gamma radiation in the soils surrounding the ICSA/RAHMAT Hostel at Ahmadu Bello University (ABU), Zaria, Nigeria. Measurements were taken at twenty sample locations using a handheld GPS and a portable gamma-ray spectrometer. Potassium-40 (⁴⁰K), thorium-232 (²³²Th), and uranium-238 (²³⁸U) count rates (CPS) and absorbed dose rates in air (nGy/h) were noted. Annual outdoor effective dose (AOED) values were estimated using established UNSCEAR conversion methods and compared to international safety guidelines. Count rates ranged from 0.48-1.40 CPS (Th-232), 1.21-1.78 CPS (U-238), and 3.46-6.92 CPS (K-40). The greatest and most reliable predictor of dosage rate was potassium (R² = 0.774). The absorbed dose rates peaked at SP3, where all three radionuclides were co-elevated, and varied from 107.5 to 196.4 nGy/h. Every sampling station above the UNSCEAR worldwide outdoor average (~59 nGy/h), which was around 2.6 times lower than the survey mean (156.1 nGy/h). Despite this, all AOED levels (mean: 0.1915 mSv/y) remained well below the ICRP public exposure limit of 1 mSv/y (~19% of the threshold). Geospatial interpolation revealed significant spatial diversity, with higher zones between SP3 and SP19 being caused by lithological heterogeneity. Even though the area has a naturally higher radiometric background and does not provide a significant radioactive risk under current occupancy estimates, continuous monitoring is recommended due to the hostel's high population density.