DNP techniques - University of Warwick
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Transcript DNP techniques - University of Warwick
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