Interlaboratory study of the ion source memory effect in ³⁶Cl accelerator mass spectrometry

Understanding and minimization of contaminations in the ion source due to cross-contamination and long-term memory effect is one of the key issues for accurate accelerator mass spectrometry (AMS) measurements of volatile elements. The focus of this work is on the investigation of the long-term memory effect for the volatile element chlorine, and the minimization of this effect in the ion source of the Dresden accelerator mass spectrometry facility (DREAMS). For this purpose, one of the two original HVE ion sources at the DREAMS facility was modified, allowing the use of larger sample holders having individual target apertures. Additionally, a more open geometry was used to improve the vacuum level. To evaluate this improvement in comparison to other up-to-date ion sources, an interlaboratory comparison had been initiated. The long-term memory effect of the four Cs sputter ion sources at DREAMS (two sources: original and modified), ASTER (Accélérateur pour les Sciences de la Terre, Environnement, Risques) and VERA (Vienna Environmental Research Accelerator) had been investigated by measuring samples of natural ³⁵Cl/³⁷Cl-ratio and samples highly-enriched in ³⁵Cl (³⁵Cl/³⁷Cl ~1000). Besides investigating and comparing the individual levels of long-term memory, recovery time constants could be calculated. The tests show that all four sources suffer from long-term memory, but the modified DREAMS ion source showed the lowest level of contamination. The recovery times of the four ion sources were widely spread between 60 – 1390 s, where the modified DREAMS ion source with values between 155 – 260 s showed the fastest recovery in 80% of the measurements.