Resonance ionisation mass spectrometry of krypton and its applications in planetary science
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Resonance ionisation mass spectrometry of krypton and its applications in planetary science I. Strashnov · J. D. Gilmour
© Springer Science+Business Media Dordrecht 2014
Abstract A new resonance ionisation time-of-flight mass spectrometer for determining krypton isotope ratios in extraterrestrial samples is presented. Laser heating is used to extract gas from mg-size samples. A cryogenic sample concentrator is employed. Atoms continuously condense on a 75 K stainless steel substrate at the back plate of a WileyMcLaren laser ion source from where they are desorbed by a pulsed 1064 nm laser and resonantly ionized in the plume. A three-colour (116.5 nm, 558.1 nm and 1064 nm) excitation scheme is used. Tuneable coherent Vacuum Ultraviolet (vuv) radiation near 116.5 nm is generated by four-wave sum frequency mixing of 252.5 nm and 1507 nm pulsed dye laser beams in a binary mixture of negatively and positively dispersive gases (Xe and Ar). Isotope effects have been observed that reduce the reproducibility of isotope ratio measurements between odd-mass, non-zero nuclear spin isotopes and even-mass, zero nuclear spin isotopes. This can be minimised and stabilised by controlling the laser fluences, experimental geometry, and the population of the magnetic sub-levels of the excited atomic states used in the ionisation process. Once stability is achieved, sample-standard bracketing (during which the known isotope ratios of a standard are determined before and after the measurements of the sample under the same conditions) allows precision and reproducibility of ∼1 % for the major isotope ratios to be achieved in samples ∼ 106 krypton atoms. Detection limits of < 1000 atoms/isotope have been demonstrated, ratios of 81 Kr in meteorites have been made with ∼5–10 % precision. Applications of the instrument in various areas of planetary science are also discussed.
Proceedings of the 9th International Workshop on Application of Lasers and Storage Devices in Atomic Nuclei Research “Recent Achievements and Future Prospects” (LASER 2013) held in Poznan, Poland, 13-16 May, 2013 I. Strashnov () School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK e-mail: [email protected] J. D. Gilmour School of Earth Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
I. Strashnov, J. D. Gilmour
Keywords Nonlinear optics techniques · Resonance ionisation · Time of flight mass spectrometry · Isotope analysis of noble gases · Planetary science · Extraterrestrial samples
1 Introduction Resonance ionisation in combination with modern ion detection techniques provides a unique opportunity for the study of isotopes that are of limited availability, such as those produced at the isotope separators of ISOLDE, CERN or Jyvaskyla, Finland where the Manchester Nuclear Physics group conducts research in collaboration with other institutions [1]. Excitation schemes have been developed for the isotopes of many elements, and work is ongoing to cove
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