Review of long term radon studies at the gran sasso underground laboratory

Abstract In this paper are presented the measurements of radon concentration taken in the period 1991 – May 1994 in the Gran Sasso Underground Laboratory, Assergi (L'Aquila), Italy. The radon level was reduced to acceptable values from the point of view of radiation protection and low background radiation to the experiments. The radon concentration depends strongly on the ventilation of the laboratory.