<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "Siderite and Dolomite as a possible tool for thermochronological use"^^ . "The present study focuses on the visualization and counting of ion-induced linear \r\ntracks in dolomite and siderite crystals by using etching and spectroscopic techniques \r\nto answer the question whether dolomite (CaMg[CO3]2) and siderite (FeCO3) are \r\nusable as fission-track dating archives. Since the uranium content in natural samples \r\ncan be highly variable, the areal density and distribution of fission tracks created by\r\nspontaneous fission of 235U in natural samples might be very variable too. Therefore,\r\nto conduct etching experiments, artificial linear tracks had to be generated. These \r\nartificial ion tracks were created on natural samples by swift heavy ion irradiation with \r\n197Au (1.10-2.18 GeV, fluence 1*106\r\nions/cm2\r\n) at the Universal Linear Accelerator \r\n(UNILAC), GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. This method \r\nproduced artificial ion tracks that were used for the etching experiments described in \r\nthis study.\r\nInduced fission tracks were created on natural samples by covering them with a \r\nuranium source (CN5 glass and zircon) and performing thermal neutron irradiation \r\n(1*1015\r\n-1*1016 neutrons/cm2\r\n) at the FRM II reactor in Munich. This method causes \r\nfission of 235U, generating fission fragments which induce fission tracks upon hitting \r\nthe mineral samples. These induced fission tracks can be assumed to be very similar \r\nin nature to spontaneous fission tracks occurring on natural samples as a result of their \r\n235U content.\r\nThe primary research objective was to visualize induced heavy ion tracks on \r\ndolomite and siderite, respectively, by using chemical etching techniques, and \r\nquantifying them with an optical microscope. For this purpose, the quality of mineral \r\nsamples was very important; when possible, samples with very smooth surfaces were \r\nused, but for siderite in particular where the available samples were too coarse, a \r\npreparation method had to be established in order to obtain high-quality, polished \r\nsurfaces. First, the established mineral etching techniques published in literature were \r\ntested for their applicability and ability to visualize induced or natural tracks on the \r\nmineral samples. In order to establish the optimal etching recipe, these etching \r\nmethods had to be slightly modified with regard to the etchant concentration, etching \r\ntime, and etching temperature, which also involved figuring out methods to conduct\r\netching at elevated temperatures (50-70 °C), safely. Ideally the etching methods \r\nshould be as safe as possible, with non-toxic etching solutions that are easy to handle\r\nIII\r\nand don’t require special safety precautions. For the visualization of ion-induced tracks \r\nin dolomite, one suitable etching solution was found: 0.001 mol/l HCl at a temperature \r\nof 20 °C, which produces roughly trigonal etch pits after 60-120 minutes of etching. \r\nTwo etchants proved capable of revealing heavy ion tracks on siderite: 10% HCl at a \r\ntemperature of 50 °C results in triangular etch pits after 10 minutes of etching, while \r\n10% H2SO4 at a temperature of 50 °C produces hexagonal etch pits after an etching \r\ntime of 30-60 minutes. These etching methods are all optimized for the areal density\r\nof tracks that an ion fluence of about 1*106\r\nions/cm2 will generate. The observation of \r\ndifferent shapes of etch pits on siderite depending on the etchant used matches the \r\ndescriptions of etching techniques found in literature, including a couple of very old \r\npublications, which also showed various etch pit shapes depending on which\r\netchant is used.\r\nAfter the etching methods for visualizing heavy ion tracks had been established, they \r\nwere tested on neutron-irradiated samples with induced fission tracks. For both\r\ndolomite and siderite, the established etching solutions also proved capable of etching \r\ninduced fission tracks generated by irradiation with fission fragments of a kinetic \r\nenergy of about 170 MeV. The results showed that the etching conditions that were \r\nused for visualization of heavy ion tracks work basically the same for visualizing \r\ninduced fission tracks. This means that dolomite and siderite are minerals that can be \r\nused as an archive for fission-track dating, as long as they have a sufficiently high \r\nuranium content.\r\nFor the purpose of conducting these irradiation and etching experiments, it was \r\nimportant to develop suitable preparation methods for mineral samples so they can be \r\nused in heavy ion irradiation or thermal neutron irradiation experiments. This was done \r\nby establishing a grinding and polishing procedure that results in very smooth mineral \r\nsurfaces, minimizing the negative effects that a natural crystal topography would \r\notherwise have on the sample’s ability to display etched tracks.\r\nThe secondary objective of this work was to test the thermal stability of induced ion \r\ntracks in dolomite and siderite, as well as studying their annealing behaviour. In the \r\ncase of dolomite, it was found that tracks generated by the heavy ion irradiation method \r\nwill anneal when the sample is heated to about 500 °C for 100 h, while natural \r\ndislocations in the samples will persist at this temperature. Therefore, this method can \r\nbe used to separate natural dislocations from artificial ion tracks. Siderite, on the other \r\nhand, decomposes when exposed to a temperature of 400 °C for 5 h, leaving only a \r\nIV\r\nblack powdery residue made up of decomposition products which are expected to \r\neither be wüstite (FeO) or graphite (C). Exposing siderite to 300 °C for 4.5 h results in \r\na thin layer of black powder on the surface, and the heavy ion tracks present on the \r\nsample could still be etched normally, meaning that in the case of siderite the annealing \r\ntemperature for ion tracks lies above the decomposition temperature.\r\nFurthermore, online Raman measurements were conducted to study the behaviour of \r\nsiderite samples during irradiation, observing changes in the sample’s structure and \r\npossible also in the chemical composition. The results showed that all three siderite \r\nbands (180, 282 and 1084 cm-1\r\n) decrease in intensity as the fluence of ions is \r\nincreased, culminating in their complete disappearance at a fluence of about 1*1012\r\nions/cm2\r\n. After the experiment was finished, the siderite sample was found to have \r\ntransformed into the same black residue seen in the annealing experiments, indicating \r\nthat siderite will also decompose when exposed to high amounts of irradiation."^^ . "2025" . . . . . . . "Baldur"^^ . "Knörr"^^ . "Baldur Knörr"^^ . . . . . . "Siderite and Dolomite as a possible tool for thermochronological use (PDF)"^^ . . . "Baldur Knörr Dissertation komplett.pdf"^^ . . . "Siderite and Dolomite as a possible tool for thermochronological use (Other)"^^ . . . . . . "indexcodes.txt"^^ . . . "Siderite and Dolomite as a possible tool for thermochronological use (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "Siderite and Dolomite as a possible tool for thermochronological use (Other)"^^ . . . . . . "preview.jpg"^^ . . . "Siderite and Dolomite as a possible tool for thermochronological use (Other)"^^ . . . . . . "medium.jpg"^^ . . . "Siderite and Dolomite as a possible tool for thermochronological use (Other)"^^ . . . . . . "small.jpg"^^ . . "HTML Summary of #36512 \n\nSiderite and Dolomite as a possible tool for thermochronological use\n\n" . "text/html" . . . "550 Geowissenschaften"@de . "550 Earth sciences"@en . .