A Walk-In Radon/Thoron Test Facility

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Abstract
Miners and mill workers can be exposed to Rn, thoron and their decay products in the U mine and mill air. Studies aimed at limiting worker exposure were developed. A large (.apprx. 26 m3) Rn/thoron test facility of the walk-in type was designed for testing and calibration of radiation instrumentation, for studying plate-out of Rn and thoron daughters on surfaces (e.g., walls), for testing and comparing radiation measuring techniques and for a variety of dynamic simulation studies of practical and theoretical relevance. The environmental conditions in the test facility were varied externally within a wide range of values. Rn and thoron concentrations from < 0.18 to > 37 Bq/l and Rn and thoron daughter working levels (WL) from < 0.02 to several WL were easily attained. The aerosol concentration can be changed from < 103-.apprx. 106 cm-3. Temperature can be varied from 15.degree.-30.degree. C; relative humidity, .apprx. 5-98%. The test facility operated as a flow-through system, enabling a variety of dynamic studies to be undertaken, or as a closed-loop with recirculation. The facility was used extensively for .apprx. 2 yr and was the only such large facility presently operating on a routine basis with thoron/thoron daughter atmospheres and Rn/thoron mixtures, in addition to the more conventional Rn/Rn daughter atmospheres. The test facility was relevent, after after some suitable modifications, to the establishment of reference standards for calibration purposes for Rn, thoron and their short-lived decay products.

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