The present study focuses on internal exposure caused by the inhalation of radon and thoron progenies because the internal exposures have not yet been clarified. For their dose assessment, radon, thoron and thoron progeny concentrations were measured by passive monitors over a long period (for 6 months). Consequently, radon, thoron and equilibrium equivalent thoron concentrations were given as 124 ± 78, 1247 ± 1189 and 7.8 ± 9.1 Bq m(-3), respectively. Annual effective doses are estimated to be 3.1 ± 2.0 mSv for radon and 2.2 ± 2.5 mSv for thoron. Total dose are estimated to be 5.3 ± 3.5 mSv a(-1). The present study has revealed that the radon dose was comparable with the thoron dose, and the total dose was ∼2 times higher than the worldwide average.
In order to evaluate internal exposure to radon and thoron, concentrations for radon, thoron, and thoron progeny were measured for 259 dwellings located in high background radiation areas (HBRAs, outdoor external dose: 3-5 mGy y) and low background radiation areas (control areas, outdoor external dose: 1 mGy y) in Karunagappally Taluk, Kerala, India. The measurements were conducted using passive-type radon-thoron detectors and thoron progeny detectors over two six-month measurement periods from June 2010 to June 2011. The results showed no major differences in radon and thoron progeny concentrations between the HBRAs and the control areas. The geometric mean of the annual effective dose due to radon and thoron was calculated as 0.10 and 0.44 mSv, respectively. The doses were small, but not negligible compared with the external dose in the two areas.
A pilot study to measure ambient gamma dose rate and radon and thoron progeny concentrations was made for eight dwellings selected in Yangjiang, China. Indoor and outdoor ambient gamma dose rates were 110-370 and 100-220 nGy h -1 , respectively. Doses received from indoor terrestrial radiation were estimated to be 0.6-1.8 mSv year -1 . Radon, thoron and thoron progeny concentrations were 19-98, 18-1120 and 0.4-10.3 Bq m -3 , respectively. This pilot study showed that the position of passive-type monitors to be placed and the deployment period should be carefully determined for estimating reliable annual average concentrations.
Roi Et is one of the provinces with rice farming and exported to many countries around the world. In order to assess the radiation risk index from Jasmine rice cultivated soils, 175 samples in Roi Et province were measured using the gamma ray spectrometry technique for estimating the natural radioactivity levels. The specific activity of 226Ra, 232Th and 40K was found from 7.14 to 29.02 Bq/kg, 7.24 to 33.40 Bq/kg and 18.17 to 129.65 Bq/kg with a mean value of 16.92 ± 1.16 Bq/kg, 16.99 ± 2.24 Bq/kg and 46.95 ± 6.79 Bq/kg, respectively. However, the values of radium equivalent activity (Raeq), the external hazard index (Hex), the gamma-absorbed dose rate (D) and the annual effective dose equivalent (AEDEout) were also calculated to evaluate radiological hazards. The average values of Raeq, Hex, D and AEDEout were found to be 44.83 Bq/kg, 0.12, 20.03 nGy/h and 0.02 mSv/y, respectively. From the results can demonstrate that the natural radioactivity from soil are not affect to population in the area, which the natural radioactivity levels and the radiation risk values of Roi Et soil samples are lower than the UNSCEAR values.
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