Study of natural background radionuclides content in mosses and other environmental samples in the Southern Thailand

Abstract

The purpose of this study is to determine the activity concentration of natural terrestrial radionuclides (238 U, 226Ra, 232Th and 40K), airborne radionuclides (210Pb, 210Pbx and 'Be) and anthropogenic radionuclide (137Cs) in naturally grooving mosses. Totally 9 moss samples from 2 different species were collected from 3 sampling sites around Hatyai city (Songkhla province), and 46 moss samples from 17 different species were collected from the 17 particular sampling localities in the National Parks and Wildlife Sanctuaries of Thailand, where are situated in the mountainous areas between the northern to the southern ends of Peninsular Thailand (7 - 12 °N, 99 102 °E). Their activity concentrations were measured using an ultra-low background gamma spectrometer. The results revealed non-uniform spatial distributions of all natural radionuclides in the study areas, while 137Cs activity concentrations are below minimum detectable activity. Principal component analysis and cluster analysis revealed the two distinguish origins of those radionuclides; furthermore, the Pearson coefficients showed the strong correlations between radionuclides in the same group (Ra, 232Th, 238U and 40K) as well as 210Pb and 210Pbx. However, not only there is no any correlation between the two distinguish groups but also with 'Be as expected, this is due to difference in their origins. The measured activity concentrations in moss samples varied largely due to the differences of moss species, topography, geology and meteorology of sampling areas. The abnormally high concentrations of some radionuclides indicated probably that a high concentration of terrestrial radionuclide in moss samples directly related to local geological features in the sampling site, or that a high level of 'Be most probably linked with topography and regional North - East monsoonal wind coming from mainland China to the Peninsular Thailand.