Applications of Fluoride Matrices in Target Materials for Heavy Element AMS Analysis

The necessity to use negative ions for injection into AMS systems which use tandem accelerators has, from its beginning, led to the use of molecular anions (negative ions) to inject the analyte atom. This strategy is required for those elements, typically metals, which have weak binding of an electron to the neutral atom and so produce very low (nA or less) beams from a sputter source. Early work used oxide beams, for example BeO [1], and oxides continue to be commonly used. While oxides provide stable target materials and beams, they are electrically insulating, so require mixing with a conducting binder. They also require powerful ion sources to generate usable currents and the presence of 3 oxygen isotopes can, in some cases, cause ambiguities in the beam that is mass-selected for injections. In 2009, Zhao et al. [2] published the results of an extensive investigation of molecular anions using fluorine, covering much of the periodic table. Not only is fluorine a mono-isotopic element, but the binding properties of molecular fluorine anions show a stoichiometric relationship which can provide useful isobar discrimination.