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RADON IN A TOURIST CAVE: A ONE YEAR CONTINUOUS SURVEY OF THE CONCENTRATIONS OF ATTACHED AND UNATTACHED RADON PROGENY AND RADON

W. Zahorowski 1 , S. Whittlestone 1 , J. James 2 and S. Solomon 3
1 ANSTO, PMB 1, Menai, NSW 2234, Australia 2 Dept. of Chemistry, University of Sydney, NSW 2006, Australia 3 ARPANSA, Lower Plenty Rd, Yallambie, VIC 3085, Australia

Radon, radon progeny and unattached radon progeny were measured in two chambers with different
characteristics at the Jenolan Caves, New South Wales, Australia, in 1996. Meteorological parameters
and condensation nucleus concentrations were measured in order to understand the processes
governing the radon concentration and degree of disequilibrium with the progeny. One chamber was
poorly ventilated, and rainfall proved to be the most important influence on radon concentration. The
other was well ventilated, and most subject to strong convective flows driven by surface temperature.
Under some conditions atmospheric pressure was an important factor.
The radiation exposure was evaluated both from the radon using a constant conversion factor, and by
the more rigorous method of using both the attached and unattached progeny as input to the
Respiratory Tract Model recommended in ICRP-66. The size dependent conversion factors were
determined for each chamber during a four day period in which activity-size distributions were
measured using a wire screen diffusion battery. The size-weighted dose conversion factors were on
average 1.7 times the conversion convention factor recommended in ICRP-65.
Keywords: Radon, radon progeny, activity size distributions, unattached fractions, ICRP Respiratory
Tract Model, dose conversion factors, show cave, diffusion battery, meteorology, seasonal variations.