Preliminary results of positive ion mass spectrometry based on a 2.45 GHz ECR ion source and a non-metallic gas target

Abstract

Positive-ion mass spectrometry (PIMS) is a positive-to-negative ion conversion metrology that just operated on the opposite of traditional accelerator mass spectrometry (AMS) on high-precision radiocarbon dating. With a higher efficient simple structure plasma ion sources instead of AMS sputter ion sources, lower ion energy (tens keV) in place of MeV, and limited footprint facility, PIMS will be a powerful competitor to AMS in the future. To precisely measure 14C, interference of molecular isobars (such as 12CH2, 13CH) will be eliminated with higher charged ions (charge state ≥ 3; molecular cations 12CH2 2+ is metastable, can be eliminated by higher stripping pressure.), nitrogen will be eliminated inside the charge-exchange cell (CXC) through charge exchanging with target gas. To demonstrate the probability of PIMS with a 2.45 GHz ECR ion source, an experiment was launched at Peking University (PKU). A compact permanent magnet 2.45 GHz ECR ion source is designed to produce carbon ions from CO2. A CXC unit was installed after the extraction system and ethylene is chosen as charge exchange gas. Preliminary experiments prove that more than hundreds of microamp of C2+ beam can be produced with this ECR source. By injecting ethylene into CXC, several microamp C- beam was detected and the C2+ ions charge exchange efficiency to C- ions can reach close to 5%.