Estimation of indoor radon levels and absorbed dose rates in air for Chennai city, Tamilnadu, India K. S. Babai • S. Poongothai • K. S. Lakshmi • J. Punniyakotti • V. Meenakshisundaram Received: 18 February 2012 / Published online: 10 March 2012 Ó Akade ´miai Kiado ´, Budapest, Hungary 2012 Abstract Indoor radon concentrations were measured inside different types of dwellings in Chennai city on a quarterly basis using a solid state nuclear track detector (LR- 115, Type II) for 1 year. Significant seasonal variations were observed. The average highest radon concentration was observed during winter (86.08 Bq m -3 ) and the lowest in summer (42.50 Bq m -3 ). The radon concentrations were also varying on the basis of different floor-covering materials. For a given season, the average maximum radon concentration was observed with cement flooring (118.96 Bq m -3 ) fol- lowed by tiles (75.25 Bq m -3 ) and marbles (74.04 Bq m -3 ). Also, outdoor soil samples were collected in and around the same dwellings and determined the radioactivity content of three primordial radionuclides ( 238 U, 232 Th and 40 K) in these soil samples using NaI(Tl) scintillation detector based gamma-ray spectrometer. Keywords Radon  Environmental radioactivity  Absorbed dose rate  Flooring materials Introduction Radon and its daughters are present in the atmosphere, especially at places where the ventilation is the lowest such as mines. Quantification of radon and their progeny, especially inside the dwellings, is necessary when deter- mining the background radiation level to the population [11]. Internal exposures due to the intake of naturally occurring short-lived daughter products of 222 Rn ( 218 Po, 214 Pb, 214 Bi and 214 Po) in the indoor environment can pose a significant risk to human health [3]. The radon concen- tration inside a room is dependent on the concentration of radium isotopes in the building materials and the porosity of the building materials. The emanation of gaseous radon from the ground is also of importance [11]. The ventilation pattern, type of building materials, topography and mete- orological parameters play a very important role in resul- tant concentration of radon in the dwellings. Subba Ramu et al. [12] also reported that ventilation and atmospheric pressure have definite influence on the levels of radon concentration. Higher radon levels are associated with igneous rocks, such as granite, and lower radon levels with sedimentary rocks with some exceptions in case of shale and phosphate rocks [5]. Human beings are exposed outdoors to the natural ter- restrial radiation that originates predominantly from the upper 30 cm of the soil [7]. The dose rates vary from one place to another depending upon the concentration of the primordial radionuclides present in soil. The presence of primordial radionuclides and their daughter products in earth’s crust, besides cosmic rays, pose exposure risks K. S. Babai (&) Meenakshi Sundararajan Engineering College, Chennai 600 024, India e-mail: ksbabai48@gmail.com S. Poongothai Faculty of Engineering & Technology, Annamalai University, Annamalainagar 608 002, India K. S. Lakshmi Meenakshi College for Women, Chennai 600 024, India J. Punniyakotti Department of Physics, Meenakshi Sundararajan Engineering College, Chennai 600 024, India V. Meenakshisundaram Radiation Safety Section, IGCAR, Kalpakkam 603 102, India 123 J Radioanal Nucl Chem (2012) 293:649–654 DOI 10.1007/s10967-012-1718-x