Abstract
This study assesses the gamma radiation levels and associated dose rates from the naturally occurring radionuclides Th-232, U-238 and K-40 in soil samples collected from the district of Rembau, Malaysia using High-purity Germanium (HPGe) Detectors. A 105 measurement were performed on surface soil using NaI (Tl) gamma-ray detector with crystal size 1 '' x1 '', covering about 83% land of the Rembau district. The concentration of the naturally occurring radionuclides Th-232, U-238 and K-40 in soil samples collected were determined by using HPGe detector based on high-resolution gamma spectrometry system at Malaysia Nuclear Agency. The range of natural gamma radiation measured was from 114 +/- 14 nGy h(-1) to 857 +/- 14 nGy h(-1). The range of activity concentrations of U-238, Th-232 and K-40 in soil from the studied areas varies from 151-401 Bq kg(-1), 113-342 Bq kg(-1) and 674-1526 Bq kg(-1) with mean values of 245 Bq kg(-1), 186 Bq kg(-1) and 1152 Bq kg(-1) respectively. The mean values of terrestrial gamma radiation dose rate measured in Rembau district is 383 +/- 18 nGy h(-1) compared to the Malaysian average is 92 nGy h(-1) and world average is 59 nGy h(-1) (UNSCEAR, 2000). The average annual dose from such terrestrial gamma radiation dose rates to an individual in Rembau district, assuming a tropical rural setting is estimated to be 0.78 mSv per year, which is considered to be within the normal range for doses from natural sources. An isodose map for the Rembau district has been plotted.