DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Dynamic Nuclear PolarisationTechniques and Mechanisms
Gavin W Morley,
Department of Physics,
University of Warwick
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Dynamic nuclear polarization (DNP)
Dynamic nuclear polarizationMore NMR signal
Applications described in next lecture
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Spin polarization
Define polarization as:
Thermal equilibrium (Boltzmann) polarization is:
n2
n1
ΔE
Ludwig Boltzmann (1844 – 1906)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Spin polarization
Boltzmann polarization:
So transfer electronic polarization to nuclei
0.01 0.1 1 10 1001E-5
1E-4
1E-3
0.01
0.1
1
Po
lari
zatio
n
Temperature (K)
Electrons
Protons
Magnetic field = 10 T
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Spin polarizationInitial polarizations: Electrons > 95%
Nuclei < 0.1%
For 8.6 T and 3 K
Boltzmann polarization:
So transfer electronic polarization to nuclei
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Nuclear magnetic resonance (NMR)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Electron paramagnetic resonance (EPR)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Electron paramagnetic resonance (EPR)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Electron paramagnetic resonance (EPR)
Overhauser DNP
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
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
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Energy of a spin system
Magnetic field, B
Magnetic field, B
Photons reflected
H = g μB B S - gN μN B I
Isidor Isaac Rabi (1898 – 1988)
S = ½ I = ½
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Energy of a spin system
Magnetic field, B
Magnetic field, B
Photons reflected
S = ½ I = ½
A
Iz = ½ Iz = -½
Gregory Breit (1899-1981)
H = g μB B S - gN μN B I
+ A S I
Isidor Isaac Rabi (1898 – 1988)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Magnetic field, B
H = g μB B S - gN μN B I + A S I
A S I = A/2 (S+ I- + S- I+) + A Sz Iz
S± = Sx ± i Sy
Energy of a spin system
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Magnetic field, B
At zero magnetic field
Triplet, F = 1: ↑↑(↓↑ + ↑↓)/√2↓↓
Singlet, F = 0: (↓↑ - ↑↓)/√2
H = g μB B S - gN μN B I + A S I
Energy of a spin system
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Energy of a spin system
Magnetic field, B
H = g μB B S - gN μN B I + A S I
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Overhauser DNP
more
Forbiddenat high magnetic fields
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Dynamic nuclear polarization (DNP)
also gets weaker at high magnetic fields
Solid effect DNP
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Dynamic nuclear polarization (DNP)
also gets weaker at high magnetic fields
Solid effect DNP
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Other DNP mechanisms
also get weaker at high magnetic fields
Cross effect Thermal Mixing
e-
e-
n
e-
e-
n
e-
e-
n
n
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Cross Effect DNP
also gets weaker at high magnetic fields
e1
e2
n
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Cross Effect DNP
See Shimon Vega’s online slides: https://www.enc-conference.org/portals/0/VegaTutorial2009.pdf
e1
e2
n
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
also get weaker at high magnetic fields
Cross effect Thermal Mixing
e-
e-
n
e-
e-
n
e-
e-
n
n
Other DNP mechanisms
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
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)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
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
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Different types of DNP system
Solid-state NMR
Liquid-state NMR
Liquid-state NMR or
MRI
Image from Griffin & Prisner PCCP (DNP special Issue) 12, 5737 (2010)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Different types of DNP system
Solid-state NMR
Liquid-state NMR
Liquid-state NMR or
MRI
Image from Griffin & Prisner PCCP (DNP special Issue) 12, 5737 (2010)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Temperature jump DNP
plus
0.01 0.1 1 10 1001E-5
1E-4
1E-3
0.01
0.1
1
Pol
ariz
atio
n
Temperature (K)
TDNP
Magnetic field = 10 T
TNMR
gain x50 from DNP and x200 from temperature jump x10,000 total
See Ardenkjaer-Larsen et al, PNAS 100, 10158 (2003)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
gain x50 from DNP and x200 from temp x10,000 total
See Ardenkjaer-Larsen et al, PNAS 100, 10158 (2003)
Temperature jump DNP
plus
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Arnaud Comment and Rolf Gruetter, Lausanne
Temperature jump DNP
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Dynamic nuclear polarization
also… ENDOR-DNP
CIDNP
PHIP
ODNP
Pulsed DNP
And then… we need nuclear spin diffusion too!
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
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
