Natural radioactivity and external dose assessment of surface soils in Vietnam

Abstract

In this study, natural radioactivity in surface soils of Vietnam and external dose assessment to human population, deduced from activities of (226)Ra, (232)Th and (40)K nuclides, were determined. From 528 soil samples collected in 63 provinces of Vietnam, including five centrally governed cities, the average activities were obtained and equal to 42.77 ± 18.15 Bq kg(-1) for (226)Ra, 59.84 ± 19.81 Bq kg(-1) for (232)Th and 411.93 ± 230.69 Bq kg(-1) for (40)K. The outdoor absorbed dose rates (OADRs) in air at 1 m above the ground level for 63 provinces were calculated, and their average value was 71.72 ± 24.72 nGy h(-1), with a range from 17.45 to 149.40 nGy h(-1). The population-weighted OADR of Vietnam was 66.70 nGy h(-1), which lies in the range of 18-93 nGy h(-1) found in the World. From the OADRs obtained, it was estimated that the outdoor annual effective dose and indoor annual effective dose to the population were 0.082 and 0.458 mSv, which are higher than the corresponding values 0.07 and 0.41 mSv, respectively, of the World. The radium equivalent activity Ra(eq) and the external hazard index H(ex) of surface soils of Vietnam are lower than the corresponding permissible limits of 370 Bq kg(-1) and 1, respectively. Therefore, soil from Vietnam is safe for the human population when it is used as a building material.

Natural radioactivity and external dose assessment of surface soils in Bolikhamxay province, Laos

“…The average radioactivity concentrations of 226 [8], it shares borders with Bolikhamxay provinceof Laos. The activity concentration of 137 Cs was not found in any of samples from Bolikhamxay province, this means that it is lower than the minimum detection limit.…”

A review on natural background radiation

“…Several studies have been carried out in countries such as Vietnam[32] and Turkey. [33] In Vietnam, the estimated outdoor and indoor annual effective doses to the population were found to be higher than the corresponding values in the rest of the world.…”

Determination of natural radioactivity in soil samples around gold mining area in Khamkeut district, Bolikhamxay Province, Laos using gamma ray spectrometer with NaI(Tl) detector

“…The external hazard index H ex is an assessment of the hazard of the natural gamma radiation. The main objective of hazard index to keep the value less than unity.H ex is defined by the following equation [2]:…”

“…The 226 Ra subseries contribute about 98% of the external γ dose induced by whole 238 U series. Radiological hazard parameters are calculated based on the specific radioactivity of 40 K, 226 Ra and 232 Th in the soil samples [1][2][3]. The low resolution energy of the NaI(Tl) detector with full width at half maximum (FWHM) is 70 keV at the 1332 keV, there are many overlapping full energy peaks of natural radiation isotopes.…”