Spatial distribution of natural γ radiation exposure and its relationship to soil types

An extensive survey of natural γ radiation dose rate levels was measured throughout the Melaka State, Malaysia. The main objective of the present study is to verify the influence of different soil types γ radiation exposures in air using statistical analyses. One-way analysis of variances ANOVA and post hoc test using Fisher’s least significant difference (LSD) were used to test the probability of significance difference between the dose rates and soil types. The survey involved 541 measurement points of terrestrial gamma radiation dose rates in an area of 1650 km² which covers five major soil groups based on six FAO/UNESCO soil orders. The spatial dose distributions and descriptive statistics of all measured γ radiation dose rates are presented. It has the mean value of 183 nGy h⁻¹. The significance test using ANOVA shows that all dose rates for four soil groups were significantly different from each other with p sig. value <0.005 and the f-ratio lies in the rejection region, f-critical (F_{α,(2, n−2)}). The post hoc test using Fisher’s LSD shows that there are two main groups of dose rates with each range 152–175 nGy h⁻¹ and 218–233 nGy h⁻¹. These two classification groups indicated the low and high range of dose rates due to the different soil groups derived from different parent rocks. An estimation of average annual effective dose equivalent to the individual in the study area was 1.12 mSv year⁻¹. For granitic soil region, the public is expected to receive slightly high effective dose of 2 mSv year⁻¹. The statistical significance test shows that the soil types significantly influenced the γ radiation exposures received by the public on the ground level.