Estimation of radon exhalation rate, natural radioactivity and radiation doses in fly ash samples from Durgapur thermal power plant, West Bengal, India
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Abstract
Coal and its by products often contain significant amounts of radionuclides, including
uranium which is the ultimate source of the radioactive gas radon. Burning of coal
and the subsequent emission to the atmosphere cause the re-distribution of toxic trace
elements in the environment. Due to considerable economic and environmental importance
and diverse uses, the collected fly ash has become a subject of worldwide interest
in recent years. In the present study, radon exhalation rate and the activity concentration
of (238)U, (232)Th and (40)K radionuclides in fly ash samples from Durgapur thermal
power plant (WB) have been measured by "Sealed Can technique" using LR-115 type II
detectors and a low level NaI (Tl) based gamma ray spectrometer, respectively. Radon
exhalation rate varied from 360.0 to 470.0 mBq m(-2)h(-1) with an average value of
406.8 mBq m(-2)h(-1). Activity concentrations of (238)U ranged from 84.8 to 126.4
Bq kg(-1) with an average value of 99.3Bqkg(-1), (232)Th ranged from 98.1 to 140.5
Bq kg(-1) with an average value of 112.9 Bq kg(-1) and (40)K ranged from 267.1 to
364.9 Bq kg(-1) with an average value of 308.9 Bq kg(-1). Radium equivalent activity
obtained from activity concentrations is found to vary from 256.5 to 352.8 Bq kg(-1)
with an average value of 282.5 Bq kg(-1). Absorbed gamma dose rates due to the presence
of (238)U, (232)Th and (40)K in fly ash samples vary in the range 115.3-158.5 nGy
h(-1) with an average value of 126.4 nGy h(-1). While the external annual effective
dose rate varies from 0.14 to 0.19 mSv y(-1) with an average value of 0.15 mSv y(-1),
effective dose equivalent estimated from exhalation rate varies from 42.5 to 55.2
microSv y(-1) with an average value of 47.8 microSv y(-1). Values of external hazard
index H(ex) for the fly ash samples studied in this work range from 0.69 to 0.96 with
a mean value of 0.77.