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Callisto

CALLISTO is a research project of an international collaboration connecting scientists of the Institute of Nuclear Chemistry of the Johannes Gutenberg-University Mainz, of the Gesellschaft für Schwerionenforschung mbH, Darmstadt, and of JAERI, Tokai, to investigate the chemistry of element 108, hassium.

It was started in 1998 with experiments about the gas-phase chemistry of the oxides of the elements osmium and ruthenium to prepare an experiment with element 108, hassium. Ruthenium, osmium and, in October/November 2002, hassium were produced in a nuclear fusion reaction. In the presence of oxygen in the target chamber, the recoils of Ru, Os and Hs form in-situ volatile oxides.
To transport the freshly produced volatile oxides out of the target chamber with a helium-oxygen mixture and without using clusters, a special target chamber was built and used successfully.
The following studies were performed:

  • The optimum mixture of helium and oxygen was determined.
  • The removal of byproducts such as 18F and 15O was investigated.
  • In order to be able to perform isothermal gas chromatography at low temperatures, water vapor had to be removed from the transport gas. To this, a drying unit was implemented.
  • To stick the volatile oxides to clusters after the isothermal gas chromatography section, a recluster chamber was installed and connected to therotating multidetector apparatus” ROMA, where the clusters are deposited on thin foils by impaction. Unfortunately, this system has only a limited deposition efficiency.
  • In order to be able to perform gas phase chemistry on reactive surfaces, small amounts of water are required. To this, a moisturizer was implemented together with a declusterizer, which is needed to evaporize water clusters, which may be formed in the moisturizing process.
  • After many preliminary investigations, the gas phase chemistry on reactive surfaces seemed very promising. The direct reaction of the gaseous oxide with a substrate finally led to a detection system, suitable for a hassium experiment. It has the advantage, that the volatile oxide is able to react with the substrate, so that we can learn more about the chemical behaviour of the volatile oxide,which is in principle impossible with the methods of cryodeposition we used formerly. So we said goodbye to this method and its limited value for the chemistry of hassium and developed an alternative, which we used in our hassium experiment in October/November 2002. More informations about this experiment will be available soon and some first and preliminary results can be found in the GSI Scientific Reports 2002.

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