Terrestrial gamma radiation dose rate and radiological health risk assessment of western region of Sarawak

Abstract

Terrestrial gamma radiation (TGR) is one of the contributors for ionizing radiation exposure to society. In this study, the baseline TGR dose rate measurement and radiological health risk assessment of west Sarawak were made. The study area covers 5 divisions; Kuching, Samarahan, Serian, Sri Aman and Betong, for a total area of 20,259.2 km2 using random sampling method as data point selection. The outdoor measurements were performed at approximately 1 meter above ground level, avoiding human infrastructures, using Ludlum 19 micro R meter NaI(Tl) scintillation detector. Twenty-nine soil samples were taken across the 5 divisions covering combinations of 9 geological backgrounds and 7 soil types. A hyper-pure Germanium spectrometer was then used to detect the samples‘ 238U, 232Th, and 40K radionuclides concentrations producing a correction factor Cf = 0.544 from linear fitting of y = 0.544x + 8.13. Excluding 2 outliers, a total of 239 data were corrected with Cf producing a mean of 47 ± 1 nGy h-1, with a range between 5 nGy h-1 – 103 nGy h-1. A multiple regression analysis was conducted between geologicallyrespective mean dose and soil types-respective mean dose against TGR dose rate, generating DG,S = 0.847Dg + 0.637Ds – 22.313 prediction model with a normalized beta equation of DG,S = 0.605Dg + 0.395Ds. The model showed 100% acceptance of sign test null hypothesis when used against TGR dose rate readings. Calculations of radiological health risk assessment produce annual effective dose equivalent of AEDE = 0.058 mSv year-1, radium equivalent dose Raeq = 140.52 Bq kg-1 and external hazard index Hex = 0.4. An isodose map was generated using kriging spatial analysis in ArcGIS 10.3 software.