A New Configuration of GSA for Size Measurements of Radon Progeny

For accurate dose assessment due to radon progeny inhalation, its size distribution is one of the most important physical parameters from the viewpoint of the dosimetric approach. A typical size distribution of the radon progeny is bimodal with unattached and attached fraction. For measuring the activity-weighted size distribution of unattached fraction, a new GSA consisted of four fine stainless steel screens with 135, 200, 400, 635-mesh and a backup filter was proposed. As the results of numerical simulation for this GSA, typically bimodal size distributions could be well reconstructed, as compared with original size distributions assumed. The calculated median diameter showed good agreement between 0.7 nm and 150 nm. The GSA performance was experimentally verified at radon/aerosol chamber experiments. The carnauba wax aerosols generated by vaporization and condensation method were used as a carrier. When the carrier aerosols were inserted into the chamber, the new GSA system caught clearly two peaks of unattached and attached fractions. The smaller peak of unattached fraction was found to be around 1 nm and its shape was very sharp like mono-disperse particles.