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 [1]. It consists of a MICADAS type negative Cs sputter ion source [2], 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 [3] 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 [4].

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.

[1] S. Maxeiner, DISS. ETH NO. 23958
[2] H.-A. Synal et al., NIMB (2007) 259
[3] A. M. Müller et al., NIMB (2010) 268
[4] A. M. Müller et al., NIMB (2015) 361


Biography:

Philip Gautschi studied Physics at ETH Zürich, where he works as a PHD student.

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Date

Nov 16 2021

Time

TUESDAY
8:45 am - 9:45 am