Periodicities of the radon level in Butte, Montana.

Hourly measurements of radon level at four houses in Butte, Montana were analyzed. Previous studies suggestes that there are diurnal cycles, spectral analysis confirms this assertion. Moreover, there are also long term trends and weekly cycles at certain locations. The periodical cycles highly suggest that indoor radon level can be dependent on the ventilation condition of the house and the activities of the residents.The relationship of indoor and outdoor radon level was investigated by cross-spectral analysis. In view of the possible different patterns caused by different seasons, data from the winter and summer are analyzed separately. The results shows that winter and summer data do display different patterns.