93Zr measurements with Accelerator Mass Spectrometry using a passive absorber

First test measurements for the detection of the long-living fission product 93Zr (T1/2=1.5.106a) were performed at the Maier Leibnitz Laboratorium in Munich. For the suppression of the isobaric background due to 93Nb, a passive absorber with a subsequent Time of Flight path and a multi-anode ionization chamber was used. From blank measurements a region of interest (ROI) for 93Zr events could be calculated by linear interpolation between 92Zr and 94Zr events. The separation of this ROI from the background events at different experimental settings was compared. In this way Silicon Nitride foils with a total thickness of approximately 2.4 mg/cm2 were determined as optimal passive absorber. An upper detection limit of 93Zr/Zr=6.10-9 was obtained. In this talk, the method of isobar separation with the help of a passive absorber is presented, and the results of the measurements using a ZrO2 blank sample are discussed.