Characterisation of reactor graphite with ion beam techniques

Full text: Activated graphite, e.g. from graphite moderated reactors contains several radioactive isotopes like ¹⁴C, ³⁶Cl, or ³H. For the final disposal of such material a quantitative characterization is demanded. We are aiming for a system which enables automated measurements using the AMS technique with gaseous samples, especially for the isotopes ¹⁴C, ³⁶Cl, and³H. The aimed system should provide a high sample throughput as well as the possibility of sample dilution in cases of high activity. Therefore, for ¹⁴C, a new gas-interface was built which uses two syringes for the transport of the sample gas into the ion source and separate reservoir for blank gas which can be used for the dilution. An advantage over the already established procedure using Liquid Scintillation Counting (LSC) is that the setup at the Cologne AMS does not need elaborate chemical sample preparation. Additionally the LSC method is less sensitive with 2·10E-4 Bq/g whereas the AMS technique can be used down to 3·10E-9 Bq/g [1]. For the measurement of the tritium concentration, we expanded our ion source test bench. A 100 kV accelerator stage with a carbon stripper foil in the centre was installed along with an additional 90° analysing magnet and a silicon detector. This will allow efficient and accurate characterisation of the activity in reactor graphite material, which is foreseen to be stored in repositories like the e.g. mine Konrad where activity limits have to be considered. In this contribution we will present the layout of our systems as well as the stage of realization. Supported by BMBF under contract number 15S9410B.