Abstract
Leaching efficiency of radon from rock was observed with fresh and weathered granites. Portions of 500 g of samples were brought into contact with a 2l of water, respectively, for the period of 1 month or more. Radon was determined by the liquid scintillation counting The observed radon concentrations ranged from 0.3 to 1.0Bq/l. The leaching efficiencies from the fresh granite were around 2%, while those from the weathered around 6%, indicating that weathering accounts significantly for the enhancement of the leaching efficiency. Microscopic surface areas of the weathered granite were larger than that of the fresh one, and a positive, but not adequate, correlation between the leaching efficiency of radon and the microscopic surface area was observed.
Depletion of 210Pb in the weathered granite was estimated to be attributed to the escape of radon into the atmosphere and the meteoric water from the outcrop during a long period of time, together with possible leaching of 210Pb itself.
