MEASUREMENT OF CONCENTRATIONS OF RADON AND ITS DAUGHTERS IN INDOOR ATMOSPHERE USING CR-39 NUCLEAR TRACK DETECTOR

This paper presents the results of the measurements of indoor Rn-222 and daughter levels in houses of different types located in different parts of Bangladesh. The passive time-integrated method of using a solid state nuclear track detector (CR-39) was employed for measuring both the Rn-222 gas concentration as well as the potential al pha energy exposure (PAEE) level from the short lived daughters of Rn-222. The Rn-222 concentration from cup exposure and the PAEE from the bare exposure were obtained directly from the track density using calibration curves. A total of 275 exposures were made in the bare mode in 15 locations and 71 exposures in the cup mode in 6 locations. The geometric mean PAEE level obtained is 9.5 mWL with a geometric standard deviation of 1.9. The corresponding value for Rn-222 concentration are 61.3 Bq.m-3 and 2.4. The total data was collected over a period of one and a half years. The monthly variation of the geometric mean of PAEE is also shown. The annual effective dose equivalent has been estimated for each location by using the conversion factor of 9 mSv per WLM as obtained from ICRP-50. The average PAEE level obtained from the total data is below the intervention level as suggested by US EPA. However, the individual averages for each location show that in 8 out of 15 locations intervention may be considered and in others no intervention is called for. The Rn-222 concentrations at the seven locations are equal or less than the equilibrium equivalent Rn-222 concentration value as suggested by EPA. Attempts have also been made to see the variation in the PAEE levels according to different type of construction material used for the houses.