Assessment of natural radioactivity levels in rocks and their relationships with the geological structure of Johor state, Malaysia

Abstract

The distribution of natural radionuclides (238U, 232Th and 40K) and their radiological hazard effect in rocks collected from the state of Johor, Malaysia were determined by gamma spectroscopy using a high-purity germanium detector. The highest values of 238U, 232Th and 40K activity concentrations (67±6, 85±7 and 722±18 Bg kg-1, respectively) were observed in the granite rock. The lowest concentrations of 238U, 232Th (2±0.1 Bq kg-1 for 238 and 2±0.1 Bq kg-1 for 232Th) were observed in gabbro rock. The lowest concentration of 40K (45±2 Bq kg-1) was detected in sandstone. The radium equivalent activity concentrations for all rock samples investigated were lower than the internationally accepted value of 370 Bq kg-1. The highest value of radium equivalent in the present study (239±17 Bq kg-1) was recorded in the area of granite belonging to an acid intrusive rock geological structure. The absorbed dose rate was found to range from 4 to 112 nGy h-1. The effective dose ranged from 5 to 138 μSv h-1. The internal and external hazard index values were given in results lower than unity. The purpose of this study is to provide information related to radioactivity background levels and the effects of radiation on residents in the study area under investigation. Moreover, the relationships between the radioactivity levels in the rocks within the geological structure of the studied area are discussed.