RESUMEN
The natural radioactivity levels all over the world can create health problems due to the inhalation of radioactive aerosols. Radon and thoron progeny content of indoor air have major contribution to natural radiation dose. In the present study, simultaneous indoor measurements of radon and thoron progeny concentrations have been carried out over a period of four months at a low activity hilly area of northern Punjab, India to see their diurnal and monthly variations. The method used for this purpose is based on the defined solid angle absolute beta counting of radioactive aerosols sampled on a filter. The average values of equilibrium equivalent radon and thoron concentrations were 5.20 Bq m(-3) and 0.235 Bq m(-3), respectively, over the period August to November 2003. Both, EECRn and EECTh show a negative correlation with temperature.