In situ measurement of terrestrial gamma dose rates in eastern region of Peninsular Malaysia and its relation to geological formation and soil types

This present study aims to obtain baseline data of environmental terrestrial radiation and to assess the corresponding health risk in the ambient environment in eastern region of Peninsular Malaysia. The measurements were taken 1 m above the soil surface using NaI [Ti] detector with a total of 2144 measured points which covered all geological formations and soil types. The measured gamma dose rates ranged from 26 nGy h−1 to 750 nGy h−1 with a mean value of 172±90 nGy h−1. The mean gamma dose rate is three times higher than world averages of 57 nGy h−1. The data of gamma dose rates show the reading of the gamma dose rates not fit to the normal distribution. The variations of gamma dose rates based on geological formation and soil types were investigated using the unbalanced one way ANOVA. The results indicated strong significant differences due to the different geological formations and soil types. The T-test of gamma dose rates for each pair of soil types or geological formations and their hypothesis test at 95 % confidential level were compared to shows the significant difference between each pairs. The results indicate that the gamma dose rates for all pairs of soil types were significant differed except the miscellaneous soil while the gamma dose rates of the pairs of geological formation were also significant differed except the intermediate and intrusive geological formations. Acid intrusive and intermediate intrusive geological formations has the highest mean values of 223 nGy h−1 and 278 nGy h−1, respectively. These values are approximately four and five times the world average. Soil type (Steep land) has the highest gamma dose rate with the mean value of 215 nGy h−1. The radiological health information which are the total annual effective dose equivalent, the collective effective dose, lifetime effective dose and the lifetime cancer risk for each person are 0.844 mSv, 3.53×103 man Sv y−1, 59.10 mSv and 3.25×10−3, respectively. The results in eastern region of Peninsular Malaysia were comparable to different areas in Malaysia, which indicate the value reported in UNSCEAR, 2000 should be adjusted to the current status in Malaysia.