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

The first application of Ar-39 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 K-39-Ar-39 isobars. In particular the use of a quartz liner in the plasma chamber of the electron cyclotron resonance ion source enabled a K-39 reduction of a factor similar to 130 compared to previous runs without liners, and allowed us to reach a detection sensitivity of Ar-39/Ar = 4 x 10(-17). order to improve this sensitivity and allow the measurement of lower ratios, higher ion source currents and a lower overall K-39 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 Ar-39 detection sensitivity required in the selection of ultra-pure materials for detectors used in weakly interacting massive particle dark matter searches. (C) 2012 Elsevier B.V. All rights reserved.