GIS predictive mapping of terrestrial gamma radiation in the Northern State, Sudan

This study presents the evaluation of absorbed dose in air due to gamma-emitting nuclides from 238U and 232Th series, 40K and 137Cs and the corresponding geographical information system (GIS) predictive mapping for the Northern State. Activity concentration of 238U, 232Th , 40K and 137Cs in soil samples collected from different locations have been measured using highresolution gamma spectrometry. On average, activity concentrations were 19±4 (238U), 47±11 (232Th), 317±65 (40K) and 2.26 Bq kg-1 for 137Cs. Absorbed dose rate in air at a height of 1 m above ground surface was calculated using seven sets of dose rate conversion factors (DRCFs) and the corresponding annual effective dose was estimated. On average, the values obtained fall within a narrow range of 44 and 53 nGy h-1, indicating that the variation in absorbed dose rate is insignificant for different DRCFs. The corresponding annual effective dose ranged from 53 to 65 μSv y-1. Using GIS, prediction maps for concentrations of 238U, 232Th, 40K and 137Cs were produced. Also, a map for absorbed dose rate in air at a height of 1 m above the ground level was produced, which showed a trend of increasing from the west towards south-east of the State. © The Author 2012. Published by Oxford University Press. All rights reserved.