Radon and Thoron Measurements at Special Underground Circumstances

In this study a comparative integrating radon (Rn) and thoron (Rn) survey executed at underground workplaces are discussed. Two types of solid state nuclear track detectors (Radopot and Raduet) were applied for survey at four sites: a manganese mine, a bauxite mine, a tourist cave and a hospital cave. Several numbers of detecting points were chosen at each site and 1-1 Raduet and Radopot detector were placed at each point. Both detector types contains two polycarbonate (CR-39) foils in different holders in order to determinate the radon as well as the thoron levels. The detectors were changed in 30-60 days periods (approximately monthly) and the survey continued for a year. This study had two aims. 1) To gain information about the radon and thoron concentrations at the chosen places including the seasonal variations. 2) To compare the performance of the two types of detectors and check their response in the special circumstances indicates by these underground places. Concerning the first point the radon concentrations were found to be as the expected ones at the given underground places and were similar to our former measurements. In the case of thoron the results are very variable and significant part of the detectors provides no data or unrealistic data. Concerning the second point there was only a little difference (<10%) between the radon results provided by the two types of detectors. In the case of thoron the two detector types showed high inconsistency. The study suggests that both types of detectors are fit for the integrating radon measurement at these special circumstances but it cannot be stated the same for the thoron measurement. The reason of the unreliability of the thoron measurement could be the high humidity (especially in the caves), the high aerosol concentration (especially in the mines) and the air change rate variation. To find the reasons needs further study.