Cluster formation restricts dynamic nuclear polarization of xenon in solid mixtures

Publication: Research - peer-reviewJournal article – Annual report year: 2012

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DOI

  • Author: Kuzma, N. N.

    Univ Penn, Dept Radiol, Philadelphia, PA 19104 USA

  • Author: Pourfathi, M.

    Univ Penn, Dept Radiol, Philadelphia, PA 19104 USA

  • Author: Kara, H.

    Univ Penn, Dept Astron & Phys, Philadelphia, PA 19104 USA

  • Author: Manasseh, P.

    Earlham Coll, Dept Chem, Richmond, IN 47374 USA

  • Author: Ghosh, R. K.

    Univ Penn, Dept Radiol, Philadelphia, PA 19104 USA

  • Author: Ardenkjaer-Larsen, J. H.

    Biomedical Engineering, Department of Electrical Engineering, Technical University of Denmark, Ørsteds Plads, 2800, Kgs. Lyngby, Denmark

  • Author: Kadlecek, S. J.

    Univ Penn, Dept Radiol, Philadelphia, PA 19104 USA

  • Author: Rizi, R. R.

    Univ Penn, Dept Radiol, Philadelphia, PA 19104 USA

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During dynamic nuclear polarization (DNP) at 1.5 K and 5 T, Xe-129 nuclear magnetic resonance (NMR) spectra of a homogeneous xenon/1-propanol/trityl-radical solid mixture exhibit a single peak, broadened by H-1 neighbors. A second peak appears upon annealing for several hours at 125 K. Its characteristic width and chemical shift indicate the presence of spontaneously formed pure Xe clusters. Microwave irradiation at the appropriate frequencies can bring both peaks to either positive or negative polarization. The peculiar time evolution of Xe-129 polarization in pure Xe clusters during DNP can be modelled as an interplay of spin diffusion and T-1 relaxation. Our simple spherical-cluster model offers a sensitive tool to evaluate major DNP parameters in situ, revealing a severe spin-diffusion bottleneck at the cluster boundaries and a significant sample overheating due to microwave irradiation. Subsequent DNP system modifications designed to reduce the overheating resulted in four-fold increase of Xe-129 polarization, from 5.3% to 21%. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4751021]
Original languageEnglish
JournalJournal of Chemical Physics
Publication date2012
Volume137
Issue10
Number of pages6
ISSN0021-9606
DOIs
StatePublished
CitationsWeb of Science® Times Cited: 3

Keywords

  • PHYSICS, HYPERPOLARIZED XE-129, EXCHANGE, STATE, NMR
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