Center for Advanced Research in Physical Sciences, Department of Physics, Fatima Mata National College (Autonomous), Kollam, Kerala India

*Email of Corresponding Author: jojo@fatimacollege.net

Wide inconsistency in indoor radon and thoron levels has been reported in the Monazite bearing densely populated regions in the coastal belt of Kerala, India. Inhalation doses are predominantly due to these gas progenies and the
unattached fraction is significant in determining radiation dose to the human lungs. The attached and unattached radon and thoron concentrations have been determined using direct radon (²²²Rn) and thoron (²²⁰Rn) progeny sensors (DRPS/ DTPS) in the Neendakara and Chavara hamlets of Kollam district, Kerala. The equilibrium equivalent concentration of the unattached fraction of ²²²Rn and ²²⁰Rn (EERCU and EETCU) was found to vary from 0.5 to 2.4 Bqm^-3 and 0.1 to 0.2 Bqm^-3, respectively. The concentrations of the attached fraction of ²²²Rn were found to be greater than the unattached fraction. The attached fraction of ²²⁰Rn progeny was in the range 1.01 to 3.8 Bqm^-3. The total (attached + unattached) equilibrium equivalent ²²²Rn concentration (EERCA+U) and total (attached + unattached) equilibrium equivalent ²²⁰Rn concentration (EETCA+U) were found to vary from 8.8 to 22.5 Bqm^-3 and 1.1 to 4 Bqm^-3, respectively. Annual effective dose rates were also determined.