Hostname: page-component-cd9895bd7-8ctnn Total loading time: 0 Render date: 2024-12-27T08:57:00.312Z Has data issue: false hasContentIssue false
  • English
  • Français

Increased 14C AMS Efficiency from Reduced Competitive Ionization

Published online by Cambridge University Press:  29 June 2016

John S Vogel  and
Jason A Giacomo
John S Vogel*
Affiliation:
University of California (retired); 8300 Feliz Creek Dr., Ukiah, CA 95482, USA.
Jason A Giacomo
Affiliation:
Eckert Ziegler AG/Vitalea Science; 2121 Second St., Davis, CA 95618, USA.
*
*Corresponding author. Email: [email protected].
Get access Rights & Permissions [Opens in a new window]

Abstract

Observation of 80 µA/mm2 C– current from a 0.5-mm-diameter sample compared to 20 µA/mm2 from a 1-mm-diameter sample contradicts the long-held surface ionization hypothesis of cesium sputter ion source operation. Resonant ionization occurs in neutral Cs plasma above a sample in a sputtered pit or well. A collision-radiation model of that plasma followed electronic excitation and radiation relaxation up to the Cs(7d) state. The Cs(5d) metastable state dominates plasma in a 1-mm-diameter well, but high electron densities in narrow wells drive a majority to Cs(7d) and higher. Competitive ionization by Al2 dimers from the sample holder reduces Cs(7s,p) states resonant in ionization energy with C–. Al anions from states above Cs(7p) in narrow wells also diminish radiation cascades to the Cs(7s,p), reducing C–. We tested sample wells of non-ionizing Zn to maintain high ionization efficiency for small samples in narrow wells.

Keywords

AMScarboncesiumanionionization
Type
Advances in Physical Measurement Techniques
Information
Radiocarbon , Volume 59 , Special Issue 3: Proceedings of the 22nd International Radiocarbon Conference (Part 2 of 2) , June 2017 , pp. 957 - 965
Copyright
© 2016 by the Arizona Board of Regents on behalf of the University of Arizona 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Barbier, L, Djerad, MT, Chéret, M. 1986. Collisional ion-pair formation in an excited alkali-metal vapor. Physical Review A 34(4):2710.CrossRefGoogle Scholar
Bullis, RH, Flavin, RK. 1964. Research on the collision probabilities of electrons and cesium ions in cesium vapors. Technical Report A-920057-3. United Aircraft Corporation, Research Labs, East Hartford, CT, USA.Google Scholar
Fallon, SJ, Guilderson, TP, Brown, TA. 2007. CAMS/LLNL ion source efficiency revisited. Nuclear Instruments and Methods in Physics Research B 259(1):106–110.CrossRefGoogle Scholar
Gnaser, H. 2008. Isotopic fractionation of sputtered anions: C− and C2 – . Nuclear Instruments and Methods in Physics Research B 266(1):37–43.CrossRefGoogle Scholar
Han, BX, Southon, JR, Roberts, ML, von Reden, KF. 2007. Computer simulation of MC-SNICS for performance improvements. Nuclear Instruments and Methods in Physics Research B 261(1):589–593.CrossRefGoogle Scholar
Kleyn, AW, Moutinho, AMC. 2001. Negative ion formation in alkali-atom-molecule collisions. Journal of Physics B 34(14):R1.CrossRefGoogle Scholar
Krishnan, U, Stumpf, B. 1992. Calculated electron excitation cross sections for excited state-excited state transitions in alkali atoms. Atomic Data and Nuclear Data Tables 51(1):151–169.CrossRefGoogle Scholar
Lee, YT, Mahan, BH. 1965. Photosensitized ionization of alkali‐metal vapors. Journal of Chemical Physics 42:2893–2896.CrossRefGoogle Scholar
Litherland, AE, Paul, M, Allen, KW, Gove, HE. 1987. Fundamentals of accelerator mass spectrometry [and Discussion]. Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 323(1569):5–21.Google Scholar
Marcum, SD, Myers, JL, Gieske, MA, Tackett, M, Ganguly, BN. 1991. The effect of radiative cascade on electron excitation temperature measurements. Journal of Applied Physics 69:27–33.CrossRefGoogle Scholar
Middleton, R. 1989. A Negative Ion Cookbook [unpublished]. Philadelphia: University of Pennsylvania.Google Scholar
Middleton, R, Klein, J. 1999. Production of metastable negative ions in a cesium sputter source: verification of the existence of N2 – and CO– . Physical Review A 60(5):3786.CrossRefGoogle Scholar
Middleton, R, Juenemann, D, Klein, J. 1994. Isotopic fractionation of negative ions produced by Cs sputtering in a high-intensity source. Nuclear Instruments and Methods in Physics Research B 93(1):39–51.CrossRefGoogle Scholar
Nalley, SJ, Compton, RN. 1971. Collisional ionization of cesium by oxygen: the electron affinity of O2 . Chemical Physics Letters 9(6):529–533.CrossRefGoogle Scholar
Narits, AA, Mironchuk, ES, Lebedev, VS. 2014. Comparative studies of ion-pair formation and resonant quenching processes in collisions of Rydberg atoms with the alkaline-earth atoms. Journal of Physics B 47(1):015202.CrossRefGoogle Scholar
Norcross, DW, Stone, PM. 1968. Recombination, radiative energy loss and level populations in nonequilibrium cesium discharges. Journal of Quantitative Spectroscopy and Radiative Transfer 8(2):655–684.CrossRefGoogle Scholar
Nørskov, JK, Lundqvist, BI. 1979. Secondary-ion emission probability in sputtering. Physical Review B 19(11):5661.CrossRefGoogle Scholar
Shanks, RP, Freeman, SPHT. 2015. Sputter-pits casting to measure AMS sample consumption. Nuclear Instruments and Methods in Physics Research B 361:168–172.CrossRefGoogle Scholar
Vogel, JS. 2013. Neutral resonant ionization in the high-intensity cesium sputter source. In: Third International Symposium on Negative Ions, Beams and Sources. AIP Conference Series 1515:89–98.CrossRefGoogle Scholar
Vogel, JS. 2015. Anion formation by neutral resonant ionization. Nuclear Instruments and Methods in Physics Research B 361:156–162.CrossRefGoogle Scholar
Vogel, JS. 2016. Anion formation in sputter ion sources by neutral resonant ionization. Review of Scientific Instruments 87:02A504.CrossRefGoogle ScholarPubMed
Vogel, JS, Giacomo, JA, Dueker, SR. 2013. Quantifying absolute carbon isotope ratios by AMS. Nuclear Instruments and Methods in Physics Research B 294:340–348.CrossRefGoogle Scholar
Vora, RB, Turner, JE, Compton, RN. 1974. Single-electron excitation and transfer in collisions of alkali-metal and oxygen atoms. Physical Review A 9(6):2532.CrossRefGoogle Scholar
Williams, P. 1979. The sputtering process and sputtered ion emission. Surface Science 90(2):588–634.CrossRefGoogle Scholar