Indirect measurement sub floor radon using passive detectors

Hourly 222Rn measurements have been made in an 80-y-old wood frame house for about 6 y. The average 222Rn concentration in the basement is 40 Bq m-3. Two holes were drilled in the slab and standard 150 cfm fans installed via a short length of PVC pipe. The air from beneath the slab was blown directly into the basement to indirectly study the long term variability in the subslab gas concentration. Passive CR-39 222Rn alpha track detectors of our design were placed weekly in the fan exit air to estimate the average subslab gas concentration. Instantaneous subslab gas 222Rn concentration was measured directly using scintillation flasks filled from adjacent floor ports once per week. The agreement with the indirect measurements was good. The average weekly basement 222Rn concentration correlated well with the weekly integrated soil gas 222Rn concentration. An increase from 44 to 74 Bq m-3 in basement air corresponded to an increase of 1.8 to 3.7 MBq m-3 in subslab soil gas. An increase in weekly average temperature from 10 degrees to 30 degrees C increased the integrated soil gas concentration from 1.8 to 3.7 MBq m-3, and an increase in average wind speed from calm to 0.5 in s-1 decreased the subslab concentration from 3.7 to 1.8 MBq m-3