The first (Mn-53/Mn-55) isotopic ratio measurements at the Cologne FN-Tandem Accelerator

A new accelerator mass spectrometer was successfully designed for the Cologne FN accelerator to enlarge the measurement capability of CologneAMS to medium mass radionuclides. With this AMS-system (Mn-53/Mn-55) isotopic ratios are measurable at a 10 MV tandem accelerator in the range of 10(-9) to 10(-10) for the first time, with a detection limit of C-L = 5.0 x 10(-12). A high Cr-53 suppression in the (Mn-53/Mn-55) isotopic ratio measurement was achieved by using the optimal silicon nitride degrader foil thickness in combination with an electrostatic analyzer (ESA). The new system opens the field of research for CologneAMS users to the medium mass region of cosmogenic nuclides, like Mn-53 for geological applications of long term erosion, exposure and burial dating and Fe-60 for nuclear astrophysical models. The presented definition of an error normalized sensitivity S-x allows an inter laboratory comparison of isotopic ratio measurements.