Studies of anions from sputtering III: The 41K background in 41CaF3− measurement by AMS

Abstract The anion KF 3 − is found to be produced from a Cs + sputter source with a relative yield of ∼10 −4 of KF 2 − , the superhalogen [1] anion of K in the target. Therefore, from CaF 2 samples, 41 KF 3 − is probably the dominant molecular ion by which 41 K background is introduced in AMS measurements of 41 Ca using CaF 3 − . Evidence is found that a source of K is the impurities in the Cs used for sputtering. The next most important molecule generating 41 K background is probably 41 K 57 Fe − due to the presence of iron in the parts of the ion source. The use of collision induced dissociation (CID) for separating CaF 3 − and KF 3 − has been investigated. The anion 41 KF 3 − has been shown to be reduced with respect to 41 CaF 3 − , by three orders of magnitude using CID at eV energies using the Isobar Separator for Anions (ISA) described in Ref. [2] . This is a degree of isobar discrimination sufficient for making very-low level 41 Ca measurements using small accelerators without the need of additional d E /d x measurement.