Radon- and thoron-produced radiation in National Park Service caves

This paper describes the findings of the National Park Service (NPS) Cave Radiation Research and Monitoring Program which has been carried on since August 1975. Two working hypotheses have been established and verified: (1) for all caves having minimal man-made disturbances to natural airflow patterns, the airborne alpha radioactivity increases in the summer and decreases in the winter in caves in which the primary cause of airflow is produced by temperature-induced density gradients and (2) two general types of physical cave configurations have been identified to relate natural cave airflows and resulting airborne alpha-radioactivity levels; up-side-down (USD) caves go up into a hillside or mountain and right-side-up (RSU) caves go down into the earth. Radioactivity levels which show the upper bounds of data obtained to date are given. A number of long-term plots of the radiation levels at various National Park Service (NPS) caves are given to show the seasonal fluctuations in both RSU and USD caves and the effects of management actions. The annual radiation exposure accumulations for personnel in various NPS caves are also given