Methodology of radon monitoring and dose estimates in Postojna Cave, Slovenia.

Due to the specific work regime in the Postojna Cave, which depends primarily on the daily number of visitors, and on seasonal variations in air radon concentrations, an optimal methodology for radon and progeny measurement and dose calculation was sought. The program of measurement throughout the years was optimized, and now comprises 3-mo exposures of etched-track detectors, and twice a year, 8-10-d measurements using continuous monitors. Radon concentrations range from about 500 Bq m(-3) in winter to about 6,000 Bq m(-3) in summer, and equilibrium factors range from 0.42 to 0.69 in winter and from 0.33 to 0.86 in summer. Radiation doses from radon decay products for employees in the cave were calculated according to the ICRP 65 methodology. The basic input data are radon concentrations and equilibrium factors at two selected locations in the cave and the records of the time spent by a worker in the cave. Effective doses received by employees annually ranged from 0.02 to 8.4 mSv.