Accelerator mass spectrometry of 41Ca with a positive-ion source and the UNILAC accelerator

The authors have made preliminary tests investigating the performance characteristics of the UNILAC accelerator system at GSI, in order to explore the sensitivity achievable in accelerator mass spectrometry (AMS) for detecting 41Ca with high-current positive-ion sources. Positively charged Ca3+ ions of up to 100 μA electrical current were injected from a Penning-sputter source and, after further stripping to Ca9+, accelerated to 14.3 MeV/nucleon. The combination of a velocity-focussing accelerator and magnetic ion-beam transport system completely eliminates background from the other calcium isotopes. Full-stripping and detection of 41Ca20+ ions with a magnetic spectrograph provides separation from isobaric 41K and, at present, a level of sensitivity of 41Ca/Ca ∼ 2 x 10-15. Future improvements and implications for dating of Pleistoscene samples will be discussed