Abstract.A portable cosmic muon detector has been developed for geophysical applications: searching for large scale underground rock/soil inhomogeneities and underground cavities. The designed muon telescope called a muon tomograph is based on the recently developed closed cathode chamber (CCC) technology, which provides a cheap, easy handling, portable, and power efficient detector system able to work even in extreme conditions (e.g. high humidity, low/high temperature). The muon telescope has a detection surface of approximately 0.1 m 2 with a 10 mrad angular resolution. Tests have been performed in natural caves and artificial tunnel systems as well. In this paper a summary of the first results on tomographic cavities are presented and the geophysical and possible industrial use of the cosmic muon tomographic technology is indicated.
Abstract:In order to use speleothems in the reconstruction of past climate and environmental changes it is necessary to understand the environmental and hydrological processes that determine the physico-chemical conditions of carbonate precipitation and hence speleothem formation. Therefore, in this study an extended monitoring program was conducted in the Béke and Baradla caves located in the Aggtelek region (Northeastern Hungary). The studied caves are rich in speleothem and flowstone occurrences with great potential for paleoclimatology studies. The monitoring activity included measurements of atmospheric and cave temperatures, CO 2 concentration in cave air, as well as chemical and isotopic compositions of water samples (drip water, precipitation) and in situ carbonate precipitates. The hydrogen and oxygen isotope compositions of drip waters showed no seasonal variation at any of the collection sites, indicating a well-mixed karstic aquifer. This implies that the isotopic compositions of local speleothems were able to record multiannual isotopic changes inherited from stable isotopes in the drip water. CO 2 concentration showed seasonality (high values in summer and low values in winter) in both caves, likely affecting carbonate precipitation or corrosion and consequently stalagmite growth. Systematic variations among Mg/Ca and Sr/Ca, Na/Ca, and Si/Ca element ratios were detected in the drip water suggesting Prior Calcite Precipitation (PCP). As PCP is characteristic of periods of reduced infiltration during drier weather conditions, the variations in drip water chemistry and drip rates indicate that the hydrological conditions also varied significantly during the studied period. This hydrological variability appears to affect not only trace element composition but also the isotopic composition of modern carbonate precipitates. In summary, these findings imply that the speleothems from the studied caves were able to record the hydrological changes resulting from alternating wet and dry periods, and therefore the geochemical data can be used to reconstruct past climate and environmental changes.
The muon intensity and angular distribution in the shallow-underground laboratory Felsenkeller in Dresden, Germany have been studied using a portable muon detector based on the close cathode chamber design. Data has been taken at four positions in Felsenkeller tunnels VIII and IX, where a new 5 MV underground ion accelerator is being installed, and in addition at four positions in Felsenkeller tunnel IV, which hosts a low-radioactivity counting facility. At each of the eight positions studied, seven different orientations of the detector were used to compile a map of the upper hemisphere with 0.85 • angular resolution. The muon intensity is found to be suppressed by a factor of 40 due to the 45 m thick rock overburden, corresponding to 140 meters water equivalent. The angular data are matched by two different simulations taking into account the known geodetic features of the terrain: First, simply by determining the cutoff energy using the projected slant depth in rock and the known muon energy spectrum, and second, in a Geant4 simulation propagating the muons through a column of rock equal to the known slant depth. The present data are instrumental for studying muon-induced effects at these depths and also in the planning of an active veto for accelerator-based underground nuclear astrophysics experiments. [34,35] that such a veto may reduce the observed background in γ-detectors typical for in-beam nuclear astrophysics experiments to a level that is close to the background in the same detectors deep underground, underlining the importance of a proper muon veto.This work is organized as follows. The underground site is described in sec. 2. Section 3 introduces the experimental setup, including the REGARD muon telescope used here, and experimental procedures. The data analysis and results are presented in sec. 4. The data are then matched, first, by a calculation based on the known rangeenergy relation, and second, by a Monte Carlo simulation using the Geant4 framework (sec. 5). A discussion is offered in sec. 6. The conclusions, a summary and an outlook are given in sec. 7. Description of the underground site studiedThe shallow-underground site Felsenkeller is located in the Plauenscher Grund district, inside the city of Dresden, Germany. The site extends along the Weißeritz river, a tributary of the Elbe, and was used as a quarry until the 18th century, then converted to a brewery, which in turn closed in 1991. The terrain is characterized by a steep cliff that runs from Northeast to Southwest, an approximately flat high plain at 200 m a.s.l. and a river floodplain at 140 m a.s.l. (Fig. 1).Nine horizontal storage tunnels were dug into the rock from 1856 to 1859. All nine tunnels have horizontal access and are interconnected in a comb-like structure (Fig. 2). The site is protected from cosmic rays by an overburden of 45 m of hornblende monzonite rock, part of the "Meißner Massiv" formation. The density of rock samples taken from the tunnels VIII and IX was here found to be (2.69±0.06) g/cm 3 . The hornblende mon...
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