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Dynamic Nuclear Polarisation Techniques and Mechanisms

Dynamic Nuclear Polarisation Techniques and Mechanisms

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Dynamic Nuclear Polarisation Techniques and Mechanisms

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  1. Dynamic Nuclear PolarisationTechniques and Mechanisms Gavin W Morley, Department of Physics, University of Warwick

  2. Dynamic nuclear polarization (DNP) • Dynamic nuclear polarization • More NMR signal • Applications described in next lecture

  3. Spin polarization Define polarization as: Thermal equilibrium (Boltzmann) polarization is: Ludwig Boltzmann (1844 – 1906) n2 ΔE n1

  4. Spin polarization Boltzmann polarization: So transfer electronic polarization to nuclei

  5. Spin polarization Initial polarizations: Electrons > 95% Nuclei < 0.1% For 8.6 T and 3 K Boltzmann polarization: So transfer electronic polarization to nuclei

  6. Nuclear magnetic resonance (NMR)

  7. Electron paramagnetic resonance (EPR)

  8. Electron paramagnetic resonance (EPR)

  9. Overhauser DNP Electron paramagnetic resonance (EPR)

  10. Overhauser DNP Forbidden relaxation Electron paramagnetic resonance (EPR) Proposal: A W Overhauser, Polarization of nuclei in metals, Phys Rev 92, 411 (1953) Followed by demonstration: T R Carver & C P Slichter, Polarization of nuclear spins in metals, Phys. Rev. 92, 212 (1953) Image from www.cnet.co.uk

  11. Magnetic resonance Photons reflected Isidor Isaac Rabi (1898 – 1988) Magnetic field, B Energy of a spin system H = g μBBS- gNμNBI S = ½ I = ½ Magnetic field, B

  12. Magnetic resonance Iz = ½ Iz = -½ Photons reflected A Isidor Isaac Rabi (1898 – 1988) Gregory Breit (1899-1981) Magnetic field, B H = g μBBS- gNμNBI + ASI Energy of a spin system S = ½ I = ½ Magnetic field, B

  13. Magnetic resonance Energy of a spin system ASI = A/2 (S+I- + S-I+) + ASzIz S± = Sx ± i Sy Magnetic field, B H = g μBBS- gNμNBI +ASI

  14. Magnetic resonance Energy of a spin system At zero magnetic field Triplet, F = 1: ↑↑ (↓↑ + ↑↓)/√2 ↓↓ Singlet, F = 0: (↓↑ - ↑↓)/√2 Magnetic field, B H = g μBBS- gNμNBI +ASI

  15. Magnetic resonance Energy of a spin system Magnetic field, B H = g μBBS- gNμNBI +ASI

  16. Overhauser DNP more Forbidden at high magnetic fields

  17. Dynamic nuclear polarization (DNP) also gets weaker at high magnetic fields Solid effect DNP

  18. Dynamic nuclear polarization (DNP) also gets weaker at high magnetic fields Solid effect DNP

  19. Other DNP mechanisms also get weaker at high magnetic fields Cross effect Thermal Mixing e- e- e- n n n e- e- e- n

  20. Cross Effect DNP also gets weaker at high magnetic fields e1 n e2

  21. Cross Effect DNP See Shimon Vega’s online slides: https://www.enc-conference.org/portals/0/VegaTutorial2009.pdf e1 n e2

  22. Other DNP mechanisms also get weaker at high magnetic fields Cross effect Thermal Mixing e- e- e- n n n e- e- e- n

  23. High-power, high-frequency sources Bob Griffin’s MIT group introduced gyrotrons to drive EPR for DNP: L R Becerra et al, A Spectrometer for Dynamic Nuclear Polarization and Electron Paramagnetic Resonance at High Frequencies, J Mag Res A 117, 28 (1995) 10 W (CW) at 140 GHz for 210 MHz in 1995 Review: Maly et al., JCP 128, 052211 (2008)

  24. Gyrotron DNP M Rosay et al, Solid State dynamic nuclear polarization at 263 GHz: spectrometer design and experimental results Bruker commercial 263 GHz gyrotron system for 400 MHz SS-NMR developed with Bob Griffin’s group

  25. Different types of DNP system Liquid- state NMR Solid-state NMR Liquid-state NMR or MRI Image from Griffin & Prisner PCCP (DNP special Issue) 12, 5737 (2010)

  26. Different types of DNP system Liquid- state NMR Solid-state NMR Liquid-state NMR or MRI Image from Griffin & Prisner PCCP (DNP special Issue) 12, 5737 (2010)

  27. Temperature jump DNP plus • gain x50 from DNP • and x200 from temperature jump • x10,000 total • See Ardenkjaer-Larsen et al, PNAS 100, 10158 (2003)

  28. Temperature jump DNP plus • gain x50 from DNP • and x200 from temp • x10,000 total • See Ardenkjaer-Larsen et al, PNAS 100, 10158 (2003)

  29. Temperature jump DNP Arnaud Comment and Rolf Gruetter, Lausanne

  30. Dynamic nuclear polarization also… ENDOR-DNP CIDNP PHIP ODNP Pulsed DNP And then… we need nuclear spin diffusion too!

  31. Conclusion • Dynamic nuclear polarization • Transfer polarization from electrons to nuclei • Flip electron spins • Overhauser effect • Solid effect • Cross effect • Thermal mixing • Use temperature jump • Use light • Use parahydrogen