Isobar separation of 93Zr and 93Nb at 24MeV with a new multi-anode ionization chamber

93Zr with a half-life of 1.6 Ma is produced with high yield in nuclear fission, and thus should be present as a natural or anthropogenic trace isotope in all compartments of the general environment. This isotope would immediately find numerous applications, however, its detection at sufficiently low levels has not yet been achieved. AMS measurements of 93Zr suffer from the interference of the stable isobar 93Nb. At the Vienna Environmental Research Accelerator VERA a new multi-anode ionization chamber was built. It is optimized for isobar separation in the medium mass range and is based on the experience from AMS experiments of 36Cl at our 3MV-facility. The design provides high flexibility in anode configuration and detector geometry. After validating the excellent energy resolution of the detector with 36Cl, it was recently used to study Iron-Nickel and Zirconium-Niobium-Molybdenum isobar separation. To our surprise, the separation of 94Zr (Z=40) from 94Mo (Z=42) was found to be much better than that of 58Fe (Z=26) from 58Ni (Z=28), despite the significantly larger deltaZ/Z of the latter pair. This clearly contradicts results from SRIM-simulations and suggests that differences in the stopping behavior may unexpectedly favor identification of 93Zr. At 24 MeV particle energy, a 93Nb (Z=41) suppression factor of 1000 was achieved based on a 93Zr spectrum obtained by interpolation between experimental spectra from the two neighboring stable isotopes 92Zr and 94Zr. Assuming realistic numbers for chemical Niobium reduction, a detection level of 93Zr/Zr below 10^9 seems feasible.