Effect of moisture on the radon exhalation rate from soil, sand and brick samples collected from NWFP and FATA, Pakistan.

A series of experiments were carried out to study the effect of the moisture content on the radon exhalation rate from soil, sand and brick samples that were collected from the North West Frontier Province and Federally Administered Tribal Areas of Pakistan, using CR-39-based radon dosimeters. After processing, samples were prepared by adding 15, 30 and 45% moisture contents (by weight) and were placed in plastic containers. The dosimeters were installed in it at heights of 25 cm above the surface of the samples. These containers were then hermetically sealed and the dosimeters were exposed to radon for 60 to 65 days. After exposure, CR-39 detectors were etched in 25% NaOH at 80 degrees C for 16 h, and track densities were counted. From the measured track densities, exhalation rate was determined using two different approaches. Maximum average radon exhalation rates of 385 +/- 86, 393 +/- 31 and 362 +/- 36 mBq m(-2) h(-1) were observed at 30% moisture content from soil, sand and brick samples, respectively. A slight decrease in exhalation rate was observed in all samples at moisture content of 45%. According to the t-test, change in the exhalation rate as a function of humidity is significant at 95% confidence level.