An optimized ion-optical setup for AMS of 10Be with a degrader foil

Full text: The challenge in Accelerator Mass Spectrometry (AMS) of 10Be (t1/2 = 1.4 Ma) is the suppression of the stable isobar 10B. One method established in recent years at VERA (Vienna Environmental Research Accelerator), is the use of a thin degrader foil to introduce an energy difference between 10Be and 10B, followed by an additional energy-sensitive bending element and a split-anode ionization chamber. While this setup has considerably reduced our background (10Be/9Be < 10-15), it initially suffered from a poor transmission after the degrader foil. In order to optimize our setup, we have measured the phase space of a 9Be2+-beam and determined the transverse emittance and energy distribution of the beam. These results were used in ion-optical simulations of our high energy beamline. They allowed to identify the beamline elements responsible for transmission losses and helped to plan modifications of our quadrupole doublet and the switcher magnet chamber. Thereby, the transmission increased by a factor of 3. Hence, the degrader foil method clearly outperforms other established methods for samples with 10Be/9Be ratios lower than 10-13. (author)