Studying 222Rn exhalation rate from soil and sand samples using CR-39 detector

Accurate knowledge of exhalation rate plays an important role in characterization of the radon source strength in building materials and soil. It is a useful quantity to compare the relative importance of different materials and soil types. Majority of houses in Pakistan are mainly constructed from soil and sand. Therefore, studies concerning the determination of radon exhalation rate from these materials were carried out using CR-39 based NRPB radon dosimeters. In this context, samples were collected from different towns of the Bahawalpur Division, Punjab and major cities of NWFP. After treatment, samples were placed in plastic containers and dosimeters were installed in it at heights of 25 cm above the surface of the samples. These containers were hermetically sealed and stored for three weeks to attain equilibrium between 222Rn and 226Ra. After exposure to radon, CR-39 detectors were etched in 25% NaOH at 80 °C for 16 h. From the measured radon concentration values, 222Rn exhalation rates were determined. It ranged from 1.56 to 3.33Bqm-2h-1 for the soil collected from the Bahawalpur Division and 2.49–4.66Bqm-2h-1 for NWFP. The 222 Rn exhalation rates from the sand samples were found to range from 2.78 to 20.8Bqm-2h-1 for the Bahawalpur Division and from 0.99 to 4.2Bqm-2h-1 for NWFP. 226Ra contents were also determined in the above samples which ranged from 28 to 36.5Bqkg-1 in the soil samples collected from the Bahawalpur Division and from 40.9 to 51.9Bqkg-1 in the samples collected from NWFP. In sand samples, 226Ra contents ranged from 49.2 to 215Bqkg-1 and 22.6–27Bqkg-1 in the samples collected from the Bahawalpur Division and NWFP, respectively. 226Ra contents in these samples were also determined using HPGe detector. The results of both the techniques are in good agreement within experimental errors.