title: Visualization of Ion-Induced Tracks in Carbonate Minerals
creator: Dedera, Sebastian
subject: 550
subject: 550 Earth sciences
description: The present study addresses the visualization of ion-induced tracks in calcite crystals by etching and spectrographic techniques with respect to the question, whether calcite (CaCO3) can be used as an archive for fission-track dating. Due to the erratic uranium content of calcite and the consequent uncertain areal density of fission tracks, artificial tracks, the ion tracks, had to be produced to create a basis of tracks which could be used for etching experiments. To create these artificial ion tracks in natural samples, calcite crystals were irradiated with swift heavy ions (2.18 GeV) at the Universal Linear Accelerator (UNILAC), GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The resulting ion tracks were used for the etching experiments described in this study.  The main research objective focused on the visualization of ion-induced tracks in calcite by etching techniques. Therefore, published etching procedures were tested for their usability to visualize induced or natural tracks on the calcite’s surface. To obtain optimal results, and to gain general knowledge about etching procedures, the existing etching recipes had to be modified. The parameters modified were the concentration of the etching agent, the etching time and the etching temperature which should not exceed 30 °C in order to avoid accidental annealing of the tracks through thermal processes within the crystal lattice. Additionally, the etching process should be as safe as possible, with etching solutions as non-toxic as possible. The experiments revealed two etching solutions suitable to visualize ion-induced tracks in calcite: Na-EDTA + 5 % acetic acid at a temperature of 21 °C, and 0.091 % HNO3 at a temperature of 15 °C. Na-EDTA + 5 % acetic acid reveals pseudohexagonal etch pits with a length of about 10 μm and a width of about 8 μm after 20 s of etching. HNO3 reveals pseudopentagonal etch pits with a length of about 9 μm and a width of about 7 μm after an etching time of 4 s. The etch pits are very shallow, with a depth of about 300 nm after 20 s, respectively 4 s of etching. Both etching procedures are optimized to reveal non-overlapping etch pits for an areal density of the tracks of 1×106 tracks/cm2. The fact that these two etching solution reveal different shapes of the etch pits confirms investigations in the literature, some of them very old, which also report different shapes of the etch pits for every etching agent used. These two etching solutions were also used successfully to etch tracks in calcite crystals induced by irradiation with fission fragments of about 170 MeV. Results showed that the etching behavior of fission fragments caused tracks is almost the same as the etching behavior of tracks caused by swift heavy ions. Additionally, the annealing behavior of the tracks was investigated. Tracks induced by irradiation with swift heavy ions anneal when exposed to temperatures of about 240 °C for 100 h, whereas natural dislocations in the crystal lattice do not anneal at this temperature. Thus annealing presents an interesting tool to distinguish between artificial tracks and natural dislocations. Overall, experiments showed, that calcite can be used as an archive for fission-track dating, if the uranium content is high enough.  The second objective dealt with the visualization of irradiation damage using non-destructive research methods. This part of the study deals with the characterization and quantification of ion-induced damage in calcite crystals by spectrographic methods. For this purpose, an online Raman measurement system was installed at the multipurpose chamber at the M3 beamline at GSI. With this system it is possible to measure Raman spectra of the samples before, during, and after irradiation with swift heavy ions. This makes it possible to detect ion-induced changes in the Raman bands of the calcite investigated. Experiments showed that calcite forms a new Raman band at 435 cm-1 at fluences above 5×1010 ions/cm2. Additionally, malachite was investigated and was found to show various changes in its Raman signal when irradiated with swift heavy ions. To obtain an independent measurement procedure for the fluence applied to a sample by irradiation with swift heavy ions, an experiment was performed based  VIII  on the photoluminescence of irradiated calcite when excited by UV light. Experiments showed that the greenish photoluminescence of irradiated areas in calcite increases in intensity with increasing fluence. This approach might be a powerful new tool to determine fluences applied to samples and has to be further developed, because it is sensitive even to very low fluences of 1×106 ions/cm2.  A third part of this thesis addresses technical issues like the preparation of samples for the irradiation with swift heavy ions. Etching experiments showed, that the surface of the calcite crystals has to be as smooth as possible, otherwise the desired etch pits will be obscured by the etched crystal-topography. Therefore, a preparation procedure for calcite samples has been developed, which produces almost perfectly smooth surfaces, which can display etched ion tracks. Additionally, a procedure was tested which is able to automatically count the etch pits on the crystals with the help of an image processing software and therefore can determine the areal density of the etch pits on an irradiated samples within seconds.
date: 2015
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/19195/1/Doktorarbeit%20Dedera%20Unibiliothek.pdf
identifier: DOI:10.11588/heidok.00019195
identifier: urn:nbn:de:bsz:16-heidok-191954
identifier:   Dedera, Sebastian  (2015) Visualization of Ion-Induced Tracks in Carbonate Minerals.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/19195/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng