Terrestrial gamma radiation dose study to determine the baseline for environmentalradiological health practices in Melaka state, Malaysia

Abstract

Environmental terrestrial gamma radiation dose rates were measured throughoutMelaka, Malaysia, over a period of two years, with the objective of establishingbaseline data on the background radiation level. Results obtained are shown intabular, graphic and cartographic form. The values of terrestrial gamma radiationdose rate vary significantly over different soil types and for different underlyinggeological characteristics present in the study area. The values ranged from54 ± 5 to378 ± 38 nGy h−1. The highest terrestrial gamma dose rates were measured over soil types of graniticorigin and in areas with underlying geological characteristics of an acid intrusive(undifferentiated) type. An isodose map of terrestrial gamma dose rate in Melaka wasdrawn by using the GIS application ‘Arc View’. This was based on data collected using aNaI(Tl) scintillation detector survey meter. The measurements were taken at 542locations. Three small ‘hot spots’ were found where the dose rates were more than350 nGy h−1. The mean dose rates in the main population areas in the mukims (parishes) ofBukit Katil, Sungai Udang, Batu Berendam, Bukit Baru and Bandar Melaka were154 ± 15,161 ± 16,160 ± 16,175 ± 18 and 176 ± 18 nGy h−1, respectively. The population-weighted mean dose rate throughout Melaka state is172 ± 17 nGy h−1. This is lower than the geographical mean dose rate of183 ± 54 nGy h−1. The lower value arises from the fact that most of the population lives in the central areaof the state where the lithology is dominated by sedimentary rocks consisting of shale,mudstone, phyllite, slate, hornfels, sandstone and schist of Devonian origin which havelower associated dose rates. The mean annual effective dose to the population from outdoorterrestrial gamma radiation was estimated to be 0.21 mSv. This value is higher than theworld average of 0.07 mSv.