Abstract: An instrument to detect submicron particles by charge-transfer attachment. The instrument is made up of a charging chamber with two concentric cylindrical electrodes, a remote third collector electrode, and a pump to force ambient air through the charging chamber and into the collection electrode. The innermost electrode of the charging chamber is supplied with a radioactive material having a gold foil covering. This material can create a small bipolar region symmetrical to the inner electrode where primary ionization takes place. Positive ions created in this region move to the larger outside unipolar region to attach themselves to submicron particles. These charged particles are then forced from the charged chamber at which time they may either impinge on the collection electrode to create a measurable axial current or the particles may enter a size discrimination chamber.