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Abstract
The research objective is to measure and analyze the specific activity of natural (40K, 226 Ra and 232Th)
and anthropogenic radionuclides (137 Cs) in 180 soil samples collected from 23 districts of Nakhon Si Thammarat
province, Thailand. Experimental results were obtained using a high-purity germanium (HPGe) detector and
gamma spectrometry analysis system at Nuclear and Material Physics laboratory in Department of Physics,
Faculty of Science, Thaksin University. The measuring time of each sample is 10800 seconds. It was found that,
the mean values of specific activity of 40K, 226Ra, 232Th and 137 Cs in soil samples ranges from 409.40 -
12600.42 Bq/kg for 40K, 10.07 - 364.43 Bq/kg for 226Ra, 10.65 - 267.93 Bq/kg for 232Th and 0.00 - 7.30 Bq/kg for
137Cs with mean values of 4313.18 ± 148.16 Bq/kg, 108.55 ± 31.19 Bq/kg, 73.95 ± 4.15 Bq/kg and 0.38 ± 0.20
Bq/kg, respectively. Moreover, the value of dose absorbed in the air (D), the radium equivalent activity (Raeq), the
external hazard index (Hex) and the annual effective dose rate (AEDout) in Nakhon Si Thammarat province has
been evaluated by using the average values of specific activity of natural radionuclides (40K, 226 Ra and 232 Th) from
this study. It was found that the dose absorbed in the air in this region was 277.09 nGy/h which was higher than
the average value of Thailand (>77 nGy/h). The radium equivalent activity in this area was 552.88 Bq/kg which
was higher than the recommended value (>370 Bq/kg). The external hazard index (Hex) was 1.49 which was also
higher than the limit set value (>1). And, the annual effective dose rate (AEDout) was 0.34 mSv/y which was
lower than the average value of the UNSCEAR report (< 0.48 mSv/y).
Keywords: Specific activity, High-purity germanium (HPGe detector), Gamma spectrometry analysis system,
Absorbed dose in air, Radium equivalent activity, External hazard index, Annual effective dose rate
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