Site-specific radon regimes of a cave system

The spatial and temporal variation of air-borne Rn-222 concentration was co ntinuously measured during 1990-94 with monthly changed etched track detect ors in the Pal-volgy and Matyas-hegy caves, Budapest, Hungary in order to i dentify site-specific behaviour of radon variations. We found winter minimu m and summer maximum levels at each measuring site. In the Pal-volgy cave t hese end values increased with the distance from the entrance. The maximum- to-minimum ratio, however, showed a broad peak between the entrance and dee p cave region. This behaviour can be attributed to the seasonal and depth d ependence pattern of the advective dilution effect caused by intrusion of o utside radon free air. Far from the entrance radon concentration goes to a saturation value, which approaches the level found in a highly unventilated remote cavity of the cave. In the Matyas-hegy cave the maximum-to-minimum ratios were small and nearly constant, indicating that the measuring sites belong to deeper par ts of the system. The higher maximum values, on the ot her hand, are attributed to smaller passage sizes of this part. High simila rity was found in the temporal variation of radon concentration in the neig hbouring parts of the two caves, which reinforced the assumed but by man un penetrable connection between them.