Dynamic Nuclear Polarisation
Techniques 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 polarization
 More 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
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Ludwig
Boltzmann
(1844 –
1906)
Spin polarization
1
0.1
Polarization
Electrons
0.01
Boltzmann polarization:
Protons
1E-3
1E-4
Magnetic field = 10 T
1E-5
0.01
0.1
1
10
Temperature (K)
100
So transfer electronic
polarization to nuclei
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Spin polarization
Initial 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
Overhauser DNP
Electron paramagnetic resonance (EPR)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Overhauser DNP
Electron paramagnetic resonance (EPR)
Forbidden relaxation
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.
Image
from(1953)
www.cnet.co.uk
92, 212
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Photons
reflected
Magnetic field, B
Energy
of a
spin
system
Isidor Isaac
Rabi (1898 –
1988)
H = g μB B S - gN μN B I
S=½
I=½
Magnetic field, B
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Photons
reflected
Iz = ½
Iz = -½
A
Magnetic field, B
Energy
of a
spin
system
Isidor Isaac
Gregory
Breit
Rabi (1898 –
(1899-1981)
1988)
H = g μB B S - gN μN B I
+ASI
S=½
I=½
Magnetic field, B
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic resonance
Energy of a
spin system
A S I = A/2 (S+ I- + S- I+)
+ A S z Iz
S ± = Sx ± i S y
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
Magnetic resonance
At zero magnetic field
Energy of a
spin system
Triplet, F = 1:
↑↑
(↓↑ + ↑↓)/√2
↓↓
Singlet, F = 0:
(↓↑ - ↑↓)/√2
H = g μB B S - gN μN B I + A S I
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Magnetic field, B
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
Forbidden
at high magnetic fields
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Dynamic nuclear polarization (DNP)
Solid effect DNP
also gets weaker at
high magnetic fields
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Dynamic nuclear polarization (DNP)
Solid effect DNP
also gets weaker at
high magnetic fields
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Other DNP mechanisms
Cross effect
Thermal Mixing
ee-
e-
n
n
n
e-
e-
en
also get weaker at
high magnetic fields
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Cross Effect DNP
e1
n
e2
also gets weaker at high magnetic fields
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Cross Effect DNP
e1
n
e2
See Shimon Vega’s online slides:
https://www.enc-conference.org/portals/0/VegaTutorial2009.pdf
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Other DNP mechanisms
Cross effect
Thermal Mixing
ee-
e-
n
n
n
e-
e-
en
also get weaker at
high magnetic fields
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
Liquidstate NMR
Solid-state NMR
Image from Griffin
& Prisner
PCCP (DNP
special Issue) 12,
5737 (2010)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Liquid-state
NMR or
MRI
Different types of DNP system
Liquidstate NMR
Solid-state NMR
Image from Griffin
& Prisner
PCCP (DNP
special Issue) 12,
5737 (2010)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Liquid-state
NMR or
MRI
Temperature jump DNP
plus
1
Polarization
0.1
TDNP
0.01
TNMR
1E-3
1E-4
Magnetic field = 10 T
1E-5
0.01
0.1
1
10
100
gain x50 from DNP
and x200 from
temperature jump
 x10,000 total
See ArdenkjaerLarsen et al, PNAS
100, 10158 (2003)
Temperature (K)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Temperature jump DNP
plus
gain x50 from DNP
and x200 from temp
 x10,000 total
See ArdenkjaerLarsen et al, PNAS
100, 10158 (2003)
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013
Temperature jump DNP
Arnaud
Comment and
Rolf Gruetter,
Lausanne
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
DNP techniques, Gavin W Morley, iMR CDT Advanced Workshop, 10th April 2013