Be-10 and Al-26 analysis with the prototype 300kV MILEA system at ETH Zurich
Mr Philip Gautschi1, Dr Marcus Christl1, Dr Christof Vockenhuber1, Dr Arnold Müller1,2, Dr Sascha Maxeiner1,2, Prof Hans-Arno Synal1
1ETH Zurich, Zurich, Switzerland, 2Ionplus AG, Dietikon, Switzerland
The construction of a new Multi Isotope Low Energy Accelerator system (MILEA) was finalized at the LIP, ETH Zürich in 2018. As a compact low energy AMS system with a maximal terminal voltage of 300 kV, it is optimized for high overall beam transport and efficiency . It consists of a MICADAS type negative Cs sputter ion source , followed by an achromatic electrostatic analyser (ESA)-magnet pair on the low energy (LE) side. The accelerator uses a 300kV solid state power supply and is equipped with a He-stripper. On the high energy (HE) side the system consists of two magnets with an ESA in between. The detection system consists of nine Faraday cups for current measurements and a two-anode gas ionization chamber (GIC), which can be optionally equipped with a gas absorber cell.
For routine Be-10 measurements at MILEA samples are prepared from BeO powder, mixed with Niobium (~1:1 molar) and then pressed into Al sample holders. The molecule BeO- is extracted and injected into the stripper at a positive terminal voltage of 220 kV. This terminal voltage was selected based on systematic transmission measurements into the 1+ and 2+ charge state for stripping energies between 50keV and 120keV. On the HE side the 2+ charge state is selected and 9Be2+ is measured as positive current (up to 5 pμA) in an offset Faraday cup. Boron isobar separation is achieved with a 75 nm Si3N4 degrader foil setup and a two anode GIC. The second HE magnet removes potentially interfering Be-9 ions  and ensures for achromatic beam transport of Be-10 into the GIC.
For Al-26, samples are prepared as AlO powder, mixed with Cu, and pressed into Cu sample holders. On the LE side masses 27 and 26 (Al-27 and Al-26) are injected sequentially into the stripper channel at a positive terminal voltage of 280 kV. On the HE side the 2+ charge state is selected and Al-27 is measured in an offset faraday cup (up to 0.3 pμA). The separation of 26Al2+ from its m/q interference 13C1+ is achieved by a gas filled absorber cell, placed directly in front of the GIC where the carbon ions are stopped due to their 50% lower energy .
This contribution presents the setup and parameters currently used at LIP for routine Beryllium-10 and Aluminium-26 measurements with MILEA, including their respective performance parameters such as blank levels, stability, linearity and overall efficiency.
 S. Maxeiner, DISS. ETH NO. 23958
 H.-A. Synal et al., NIMB (2007) 259
 A. M. Müller et al., NIMB (2010) 268
 A. M. Müller et al., NIMB (2015) 361
Philip Gautschi studied Physics at ETH Zürich, where he works as a PHD student.