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Please use this identifier to cite or link to this item: http://hdl.handle.net/1807/32706

Title: A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction Studies
Authors: Eliades, John Alexander
Advisor: Davis, Donald W.
Litherland, A. E. (Ted)
Department: Geology
Keywords: radio frequency quadrupole
rf quadrupole
accelerator mass spectrometry
AMS
gas-phase reactions
isobar suppression
anion
negative ion
chlorine
Cl
36Cl
carbon trimer
C3
sulphur
sulfur
sulphur oxide
sulfur oxide
SO
methane
CH4
nitrogen dioxide
NO2
nitrous oxide
N2O
oxygen
O2
argon
Ar
strontium
Sr
90Sr
SrF3
yttrium
Y
zirconium
Zr
ZrF3
trace isotope analysis
superhalogen anion
secondary ion mass spectrometry
SIMS
Cs sputter ion source
rf quadrupole ion trajectory simulation
anion gas reactions
negative ion gas reactions
gas-phase anion reactions
S- + NO2
SO- + NO2
S- + N2O
S- + O2
S- + Ar
Cl- + NO2
Cl- + Ar
Cl- + CH4
SrF3- + NO2
YF3- + NO2
ZrF3- + NO2
C3- + NO2
Issue Date: 21-Aug-2012
Abstract: A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified.
URI: http://hdl.handle.net/1807/32706
Appears in Collections:Doctoral

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