³⁶Cl and ¹²⁹I at ASTER and DREAMS

At ASTER (Accélérateur pour les Sciences de la Terre, Environnement, Risques) and DREAMS (DREsden Accelerator Mass Spectrometry) sophisticated ion sources are used for ³⁶Cl and ¹²⁹I. Both facilities have dedicated ³⁶Cl chemistry labs. At DREAMS it is also used for storage and pressing of AgCl in sample holders (SHs). Most ³⁶Cl-AMS labs, reduce the isobar ³⁶S from the SH by a labor-intensive AgBr-backing. Though, at ASTER and DREAMS only ultrapure Ni and Cu is used, respectively. To find out the pros and cons of the two materials, we have (a) exposed AgCl pressed in Ni and Cu to air (in the dark). After 2 h only, cauliflower-type NiCl₂ (analysed by EDX) has been formed from AgCl and Ni preventing any later AMS, whereas AgCl in Cu after 3 days looks unweathered and is still measurable. (b) compared S-decline in AgCl pressed in Ni and Cu (ASTER SHs). After ∼5 min S decreases by a factor of ∼5 for both reaching the same low S-rate after 20 min. However, S is higher at 5-20 min in Cu showing that Cu is contaminated at the surface. High S is not seen at all at DREAMS for DREAMS Cu SHs. Thus, chemical etching and controlled storage of Cu SHs might be a cheaper and better alternative for ³⁶Cl-AMS.
For ¹²⁹I AMS a sophisticated tuning strategy is minimising sputtering of any iodine containing material at DREAMS.