Anion formation by neutral resonant ionization

Increased 14C AMS Efficiency from Reduced Competitive Ionization

“…We confirm that ionization of sputtered Al and/or Al 2 from the sample holders reduce C – ion output by competitive ionization. Competitive ionization also explains how Ir and Pt powders in 36 Cl samples reduce 36 S from the ion source (Vogel 2015) and why Cu sample holders halve C – output. Further support for the resonant electron transfer theory is obtained from our explanations of several “mysteries” in Middleton’s Negative Ion Cookbook (Middleton 1989), such as the increased ion output of Al – , Fe – , and Cs – , from narrow-diameter sample wells (Vogel 2015).…”

“…Shanks and Freeman (2015) demonstrate that small C samples, recessed in 0.5-mm ⌀ wells having Fe-coated walls, produce as much C – current as larger samples in 1-mm ⌀ wells in Al holders. We attribute this to competitive ionization for Cs(7s) by sputtered Al 2 and by Al ionizing states above Cs(7p), reducing its production from cascade radiation, as indicated in Figure 2 (Vogel 2015). Fe-coated walls eliminate this competitive ionization from both Al and Al 2 .…”

“…Sulfur removes the Cs(5d) target atoms for exciting Cs to Cs(7p) and higher. Sulfur’s high probability of ionization from the copious Cs(5d) makes even slight traces of 36 S in 36 Cl AMS samples into serious background that can be reduced by adding iridium to the sample (Vogel 2015). Middleton (1989) shows the aluminum dimer dominates sputtering from that metal.…”

Sputter-pits casting to measure AMS sample consumption

“…This may mean that the ion source only extracts useful beam from the central region of the caesium focus and very little from the walls of the sputter pits assuming surface ionisation. Alternatively, the currents can be explained by the formation C À anions through Neutral Resonant Transfer (NRT) by a Cs plasma in the pit of a cathode as presented by Vogel in these proceedings [7]. In addition to the sleeve acting as sacrificial material, it will also define a 0.5 mm diameter plasma channel, which is better suited to generated the optimal excited states of Cs for NRT than the normal 1 mm channel (or a 0.28 mm (RMS) Gaussian pit).…”

GGR Biennial Critical Review: Analytical Developments Since 2014

“…The accelerated ions were produced when excited states of neutral Cs underwent resonant electron transfer with neutral sputtered atoms from the sample. The model was able to explain increased ion output of Al − , Fe − and Cs − from narrow‐diameter sample wells and identify metal binders for reduced interference production (Vogel ), for example, Nb is a better metal additive for BeO than Ag.…”