title: Bimodal unattached 218Po Radon progeny and the influence of enhanced deposition effect at high-radon levels.
abstract: Unattached fraction (218)Po airborne particle size distributions from graded screen array diffusion batteries are analysed for bimodal constituents. The analysis is for the high (222)Rn concentration range from 10 to 50 kBq m(-3) where the recently reported enhanced deposition effect is in transition. We find that the single unattached fraction is distributed nominally at an arithmetic mean diameter (AMD) of 0.8-1.0 nm, and consists of two (218)Po molecular species with AMD congruent with 0.756 and 1.101 nm, respectively. In unfiltered room air the 0.756 nm species is the least stable, decreases monotonically in concentration magnitude beginning at 12 kBq m(-3) and disappears completely at approximately 32 kBq m(-3) (at a relative humidity of 54%). The AMD congruent with 1.101 nm mode does not become unstable until it reaches approximately 32 kBq m(-3) (222)Rn level and completely disappears at approximately 50 kBq m(-3). Similar behaviour is observed for filtered air but with some distinct differences. This work supports the bimodal findings for the (218)Po unattached fraction of Porstendorfer and co-workers and provides further details of the high-radon enhanced deposition effect.
authors.affiliation: International Academy, 693 Wellerburn Road, Severna Park, MD 21146, USA. vfleonard@worldnet.att.net
authors.forename: Bobby E
authors.initials: BE
authors.lastname: Leonard
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis* / Q000737:chemistry*; D000465:Algorithms; D001417:Background Radiation; D003198:Computer Simulation; D008956:Models, Chemical; D015233:Models, Statistical; D010316:Particle Size; D011059:Polonium / Q000032:analysis* / Q000737:chemistry*; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods* / Q000592:standards; D017687:Radon Daughters / Q000032:analysis* / Q000737:chemistry*; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors
chemical_list: D000396:Air Pollutants, Radioactive; D017687:Radon Daughters; D011059:Polonium