Abstract: Device for analyzing the activity of a radioactive aerosol as a function of the grain size distribution of its particles of the type comprising a tight enclosure, means for circulating the aerosol through said enclosure and within the latter, a plurality of stages for collecting aerosol particles with a given grain size, each of the stages comprising an aerosol injection plate perforated by at least one calibrated opening and a collection plate for particles of a given grain size, wherein it comprises means for establishing an electric field between the injection and collection plates of each of the stages with a view to establishing an ionization current through a stage during the disintegration of the particles collected in the latter and means for measuring the ionization current of one of the said stages.