In order to get a feeling for the exhalation of radon from granites a very simple radon chamber was built. The commercial radon monitor SIRAD MR-106N from Sinmor was used.
The concept of the measurement is based on the experience that the direct radiation influence from the granite on the detector is negligible. Further it is sufficient to just observe the pile-up of radon to get a coarse quantitative impression, since the pile-up also occurs with the half life time constant. When an exponential function is fitted to the measurement in the least mean square sense using the half life constant of radon of 3.8 days the steady stade final activity can be estimated with extrapolation.
As a measurement chamber a 10.4litre container was used with a large twist off cap equiped with a gas-tight rubber seal (as used for canoeing). The bottom is filled with granite stones and the radon monitor is place on a small table above the stones.
In the following the results of the measurements are listed.