Some recent developments and applications of nuclear track microfilters

Experiments were performed to produce new types of nuclear track microfilters with improved characteristics. Track development conditions were systematically varied with a view to modify shape and geometry of the etched channels in Muscovite mica track detectors. Relativistic and semirelativistic ions of 238U and 139La were used to drill etched channels about 1 mm long in CR-39 polycarbonate track detectors. A novel approach was made to produce 'through'-holes in 150 μm thick CR-39 plastic sheets using alpha particles from natural alpha sources. Mica nuclear track microfilters were used in a three-stage particle fractionator in order to study the size and activity distributions of the aerosols collected in an industrial area and in radon-rich laboratory air. The results indicate that the use of these improved filters, besides increasing the air through-put, is very useful in separating aerosols of different sizes, and radon and thoron from their mixtures. (orig.)