Small System for Precision Ultra-sensitive Trace Mass Spectrometry of Carbon-14 and Other Selected Nuclides

摘要

A method of measuring in small samples the ultra-trace amounts of C-14 relative to C-12,13 in a background of N-14, comprises the following steps: the sample isphysically and chemically processed depending upon the final sensitivity desired; the sample is injected into an ICP, which functions as a source of positive ions with energies up to a few tens of KeV, and as a molecular dissociator of order parts-per-trillion; the ions then analyzed with conventional Electrostatic and Magnetic spectrometers, which monitor the ion beams with adjacent masses and transmit the ion species of interest through defining apertures; the transmitted ions are refoccused and accelerated to an energy of order tens of KeV; the positive ion beam strikes a thin foil or supersonic gas-jet canal where some of the beam intensityemerges with negative charge, eliminating atomic isobar backgrounds that cannot form negative ions, and as an additional molecular ion dissociator; the transmitted Negative ions are refoccused and accelerated by a few more tens of KeV; the ionsare then analyzed with conventional Electrostatic and Magnetic spectrometers, through a final defining aperture and onto a detector. Similar configurations may be used to measure ratios of other long-lived radio- to stable-isotopes whose com-peting stable atomic mass-isobars cannot form negative ions, such as: 26Al/27Al in a background with 26Mg; 55Fe/54Fe in a background with 55Mn; 129I/127I in a background with 129Xe, Similar configurations may be used for direct measure of platinum group elements (PGE), actinides (ACT), etc., when atomic-isobars need not be distinguished.