Abstract: This research addresses problems in conducting continuous monitoring of α aerosols at decommissioning sites.According to the theoretical analysis and experiment results, the method of nuclide natural background compensation was used, realized the spectrum forword trailing compensating of natural background.The compensating efficiency is greater than 90%.An α aerosols continuous monitoring system was set up using natural background correction technology and the differentiated particle size sampling technology. The detection sensitivity for Pu aerosols in 25 minute is 0.02 Bq·m^-3 when the concentration of radon thorium progeny is 100 Bq·m^-3.

Key words: decommissioning of nuclear facilities, α aerosol, continuous monitoring