An evaluation of the level of naturally occurring radioactive material in soil samples along the Chao Phraya river basin

The aim of this study was to evaluate the level of natural radioactivity in river sediments and riverbank surface soils collected along the Chao Phraya River and its tributaries in Thailand. The activity concentrations of radionuclides in 238U and 232Th decay chains as well as 40K in all samples have been determined by means of a gamma-ray spectrometry system using a hyper-pure germanium detector in a low background configuration. The ranges of specific activity for 226Ra, 232Th and 40K were found to be 15.2–67.0, 16.8–73.3 and 204.6–656.5 Bq kg−1, respectively. Additionally, evaluations have been made of the absorbed gamma dose rate in air and the annual effective dose equivalent from outdoor terrestrial gamma radiation in order to assess any excess radiological risk from agricultural usage of fertilizers. In this study, the absorbed dose rate was observed to vary from 30.5 to 102.6 nGy h−1 and the outdoor annual effective dose equivalent to range from 37.4 to 125.8 μSv yr−1.