C− generation by charge exchange with non-metallic gas for positive ion mass spectrometry

Abstract

Carbon positive ion mass spectrometry technology(C-PIMS) is a new type of mass spectrometry technology using the opposite charge exchange process of accelerator mass spectrometry (AMS). There is a plan at Peking University to build 14C-PIMS with the study of a compact 2.45 GHz ECR ion source for C2+ production and a charge exchange cell (CXC) for C2+ to C− conversion. In this paper, the profile of carbon ion source and CXC is introduced and the generation of C− ions is investigated. In experiment, five non-metallic gas targets are tested. 19 μA@90 keV C− beam is obtained from C2+ using the ethylene target. It is found that gas targets with low first ionization energy favor the generation of C−. In addition, the charge exchange efficiency at different beam energies (25 keV–90 keV) is investigated. In terms of theory, the mechanisms of resonant and non-resonant charge exchange processes are introduced to analyze the experimental results. Moreover, the charge exchange from C+ to C− is studied and the feasibility of C+-PIMS is discussed since 2.45 GHz ECR ion source produce more C+ ions. It is found that 139 μA@45 keV C− beam can be obtained from C+ using the methane target.