Reducing potassium contamination for AMS detection of 39Ar with an electron-cyclotron-resonance ion source

Abstract The first application of 39 Ar Accelerator Mass Spectrometry (AMS) at the ATLAS facility of Argonne National Laboratory was to date ocean water samples relevant to oceanographic studies using the gas-filled magnet technique to separate the 39 K– 39 Ar isobars. In particular the use of a quartz liner in the plasma chamber of the electron cyclotron resonance ion source enabled a 39 K reduction of a factor ∼130 compared to previous runs without liners, and allowed us to reach a detection sensitivity of 39 Ar/Ar = 4 × 10 −17 . In order to improve this sensitivity and allow the measurement of lower ratios, higher ion source currents and a lower overall 39 K background are necessary. This paper summarizes our efforts to investigate new methods combining low level potassium cleaning techniques with the use of ultra-pure aluminum liners in the plasma chamber of the ion source. The aim of the study was to improve by 1–2 orders of magnitude the 39 Ar detection sensitivity required in the selection of ultra-pure materials for detectors used in weakly interacting massive particle dark matter searches.