This draws in warmer air through the shafts on the mountains, which cools down in the mountain. The colder and heavier air flows from the tunnel openings into the warmer valleys. During the day, it’s the other way around. At night, colder and heavier air penetrates from the valleys into open galleries, heats up in the mountain, and is forced out through the shafts on the mountains. The reason for the fluctuations in the radon activity concentration in mines is the density-driven flow through the mines caused by the outside temperature. 1 shows an example of the course of the radon activity concentration in the gallery Querschlag 68 in Schneeberg ( Dehnert 2016a). Radon activity concentrations of 50,000 Bq m −3 to 100,000 Bq m −3 are not uncommon at underground construction sites at old mines, and 1 million Bq m −3 can also be reached. The radon potential in the Erzgebirge is high. They repair mining damage and ensure that houses and roads remain safe in the future and that mine water can drain into the rivers through galleries. Around 250 miners from eight companies are permanently employed in remediation work at old mining sites. Many of them are located near the surface under towns, villages, and roads. Long-lasting mining has left countless galleries and shafts in Saxony. Saxony and the Czech Republic have applied for the Montanregion Erzgebirge to be included in the United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage List as a montane cultural landscape. Mountain parades and Mettenschichten have become landmarks of the region. The historical witnesses to medieval mining and Wismut mining are lovingly remembered in Saxony. There are many indications that more mines will be added, and the Erzgebirge is at the beginning of a fourth Berggeschrey for lithium, tungsten, tin, and fluorspar. Today there are three mines in Saxony where fluorspar, lime, and kaolin are mined. A third Berggeschrey began in 1946 because of the uranium mining of the company SDAG Wismut. The second Berggeschrey was based on rich silver ore deposits in 1470 in Schneeberg and shortly afterwards in 1491 near Annaberg-Buchholz. The first Berggeschrey was triggered by the silver findings in the 12th century near Freiberg. Times of intensive mining are called “Berggeschrey” in the Erzgebirge. Mining began shortly thereafter and continues to this day at varying intensities. In 1186, the first silver was found in the Saxon Erzgebirge. In future, reference dosimeters and the measurement of a reference value will not be necessary. A uniform reference value for the radon activity concentration of 50 Bq m −3 was used for all boxes to determine the exposure of miners during working hours. The miners stored their dosimeters in the boxes outside working hours. To solve the problems, reference dosimeters were replaced by radonproof boxes with activated carbon cartridges inside. The conditions of use (storing dosimeters along with a reference dosimeter) were often not met by the miners. In mining practices, this method has caused problems. For this purpose, the exposures of the reference dosimeters that have occurred outside working hours are subtracted from the exposures of the miners’ dosimeters. After a 3 mo wearing period, the dosimeters are replaced and the miners’ exposures are determined. Outside the miners’ working hours, the dosimeters must be stored together with a reference dosimeter. The dosimeters consist of diffusion chambers with CR-39 nuclear track detectors. For this reason, the miners are monitored with personal radon dosimetry. Despite radiation protection measures, exposures to more than 6 mSv occurred among 22 miners in 2016 alone. About 250 miners are permanently engaged in rehabilitation work at old mining sites so that houses and roads are safe and the mine water can drain through galleries. In 1168, the first silver was found in the Saxon Erzgebirge.
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