Indian Journal of Pure & Applied Physics Vol. 48, July 2010, pp. 520-523 Measurement of radon activity, exhalation rate and radiation doses in fly ash samples from NTPC Dadri, India Mamta Gupta 1 *, A K Mahur 2,3 , R G Sonkawade 4 , K D Verma 1 & Rajendra Prasad 2,3 1 Department of Physics, S V (P G) College, Aligarh 202 001, India 2 Department of Applied Physics, Z H College of Engg & Tech, AMU, Aligarh 202 002, India 3 Vivekananda College of Technology and Management, Aligarh 202 002, India 4 Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067, India E-mails: guptaapd1@yahoo.co.in, ajaymahur345@rediffmail.com Received 22 April 2010; accepted 7 May 2010 Radon activities and radon exhalation rates have been measured in fly ash samples from NTPC (National Thermal Power Corporation), Dadri situated in Uttar Pradesh, using “Can technique”. This technique employs LR-115 type II solid state nuclear track detectors fixed at the top of the “Can” filled with fly ash samples. Radon activity has been found to vary from (222.56 ± 25.8) to (673.68 ± 45.1) Bqm -3 with an average value of (431.71 ± 35.5) Bqm -3 . Surface exhalation rate has been found to vary from (80 ± 9) to (243 ± 16) mBqm -2 h -1 with an average value (155 ± 13) mBqm -2 h -1 , whereas mass exhalation rate has been found to vary from (3.1 ± 0.4) to (9.34 ± 0.6) mBq kg -1 h -1 with an average value of (5.98 ± 0.5) mBqkg -1 h -1 . Indoor inhalation exposure (radon) effective dose has also been estimated which is found to vary from (5.8 ± 0.7) to (17.6 ± 1.2) μSvy -1 with an average value of (11.3 ± 0.9) μSvy -1 . Keywords: Radon, Fly ash, LR-115 type II SSNTDs, Radon exhalation rate, NTPC Dadri 1 Introduction Coal contains naturally occurring radio nuclides arising from uranium and thorium series. Burning of coal and the subsequent emission to the environment from the thermal power plants are one of the sources of the technologically enhanced exposure of human beings from the natural radio nuclides. It is well established that Indian coal has high ash contents and an average of ~100 million tones of fly ash is produced per annum in India 1-3 . Earlier studies have shown that Indian coals contain 1.8-6.0 ppm 238 U and 6.0-15.0 ppm of 232 Th 4 . But recent studies have indicated as high as 50 ppm 232 Th and 10 ppm 238 U in pond ash generated from coal combustion 5 . Coal ash is used in a variety of applications. The use of fly ash in the production of concrete bricks and blocks is most widespread. Fly ash based light weight building materials are also being produced. Thus fly ash produced by coal-burning in thermal power stations is important. It may raise the concentration of airborne indoor radioactivity to unacceptable levels, especially in places having low ventilation rates places. A large variation in radon activity is observed in dwellings, as the uranium concentration in natural materials used as building materials vary in a wide range and from place to place. In the previous measurements 6 , fly ash was found to contain enhanced level of uranium as compared to coal. Because of its small size and hence large surface area, it has greater tendency to absorb trace elements that are transferred from coal to waste products during combustion 7 . Radon exhalation rate is of prime importance for the estimation of radiation risk from fly ash samples, used for building construction materials. Due to low level of radon emanation from building materials, long term measurements are required for which solid state nuclear track detectors can be used effectively and conveniently. In the present study, radon activity and radon exhalation rate have been measured in fly ash samples collected from NTPC (National Thermal Power Corporation) Dadri, situated in state of Uttar Pradesh in India. Indoor inhalation exposure (radon) effective doses have also been estimated from the radon exhalation rate. The aim of study is the possible health risk assessment in the area associated with the utilization of fly ash. 2 Experimental Details 2.1 Radon exhalation rate measurement Fly ash samples collected from NTPC, Dadri, were dried and sieved through a 100 mesh sieve. For the