J. Kohlbrecher, Polarized Solid Targets, Honnef 2003 Dynamics Of Nuclear Spin Polarization J....

J. Kohlbrecher, Polarized Solid Targets, Honnef 2003

PAUL SCHERRER INSTITUT

Dynamics Of Nuclear Spin Dynamics Of Nuclear Spin PolarizationPolarization

J. Kohlbrecher

Paul Scherrer InstituteCH-5232 Villigen

Switzerland

B. van den Brandt, P. Hautle, J. Kohlbrecher,

J.A. Konter, S. Mango (PSI)H. Glättli, E. Leymarie (CEA-Saclay)I. Grillo, R. May (ILL)H. Jouve, H.B. Stuhrmann (IBS)O. Zimmer (TU München)

investigated by simultaneous NMR investigated by simultaneous NMR and and

polarized neutron scatteringpolarized neutron scattering



DNP: a two step process

How to measure clusters of polarized protons

1. scattering of polarized neutron on polarized nuclei

2. small angle neutron scattering (SANS)

model system: EHBA-Cr(V)

time-resolved SANS and NMR experiments

Dynamics Of Nuclear Spin Dynamics Of Nuclear Spin PolarizationPolarizationinvestigated by simultaneous NMR investigated by simultaneous NMR

and polarized neutron scatteringand polarized neutron scattering

Contents:Contents:

Joachim Kohlbrecher



• protons close to electron polarize first

• time constant: ttpolpol < 1 s < 1 s

electron

1.1.

proton

polarization diffuses to the bulk protons by flip-flop transitions

time constant: tdiff » few seconds

2.2.H0

DNP: a two step processDNP: a two step process

close protons: ● strongly coupled to the p.c.

● weakly coupled to the bulk

● “poorly visible" by cw-NMR

bulk protons: ● weakly coupled to the p.c

● "visible" by cw-NMR

paramagnetic centre generates strong local field

• microwave induced direct interaction falls off like r6



How to measure How to measure clusters of polarized protonsclusters of polarized protons

requirements for experimental method:

1. sensitive on polarization of protons2. sensitive on length scale in nm-range

what do we want to see:

1. time-dependent polarization built-up of the proton spins around the radical

2. and in the bulk

experimental method:

1. cw-NMR (bulk protons)2. neutron scattering technique (close

protons)



Neutron scattering techniquepolarized neutron scattering on polarized polarized neutron scattering on polarized

nucleinucleicold neutrons and their interaction with matter

2

21

b

E

VEn

kin

kinn

refraction indexinteraction potential for a single atom

)(2

)(2

jjN

bm

V rrr

» range of V(r)

scattering length

wavelength: 4 Å frequency: 1.2 THzenergy: 5meV wavevector:

1.55 1/Åvelocity: 980 m/s temperature: 58 K

b scattering lengthdensity



parallel

neutron

isotopes =

½I = ½

b = b0 + bnI.s

spin dependent scattering length

neutron

isotopes =

½I = -½

antiparallel

Polarized neutron scattering Polarized neutron scattering on polarized nucleion polarized nuclei

proton:

b0 = -0.374 bn = 5.8254

- 2 - 1 0 1 2

scattering length <b> / 10- 12cm

1H2H12C14N16O

Pp=-1

Pp=1



How to measure How to measure clusters of polarized protonsclusters of polarized protons

requirements for experimental method:

1.1. sensitive on polarization of protonssensitive on polarization of protons2. sensitive on length scale in nm-range

what do we want to see:

1. time-dependent polarization built-up of the proton spins around the radical

2. and in the bulk

experimental method:

1. cw-NMR (bulk protons)2. neutron scattering technique (close

protons)



sample

scatteredneutrons

detector

incidentneutrons,

d 2sin

42

Qd

λ ≈ 0.5 nm

d ≈ 10 nmθ ≈ 3 deg

Small Angle Neutron ScatteringSmall Angle Neutron Scattering

neutronguide

velocity selector(mechanical)

iris for beam collimation

sample

primary beam stop

2-dimensionalposition sensitive

detector

Qk

k

0

2

2



Formfactor in Formfactor in SANSSANS

2

3

23

)(

)cos()sin(3

3

4,,

QR

QRQRQRRRQI

shapeheight

0 1 2 3 4 5 6 7 80.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0 R=0.45nm, b2=1

R=0.45nm, b2=1.2

R=0.5nm, b2=1

R=0.5nm, b2=0.53

I(Q

) /

a.u

.

Q / nm-1



-0.1

-0.05

0

0.05

0.1

-10 -5 0 5 10

radius [Å]

scatt

eri

ng

len

gth

den

sit

y

P=-1 P=0 P=1

P=1

P=0

P=-1

21312

321

3121 )()()()(),,( QRFRQRFRPQRFRAIRRQI soshsocinc

Shell of polarized protons:

-0.1

-0.05

0

0.05

0.1

-10 -5 0 5 10

radius [Å]

scatt

eri

ng

len

gth

den

sit

y

P=-1 P=0 P=1

P=1

P=0

P=-1

R1

R2

[CrVO7C4]-

[C2H5]4

glycerol-water (80% ….. 98% deuterated)

bulk protonelectron close proton

Model System:Model System: EHBA-Cr(V) EHBA-Cr(V)

close protons

sample E5 (solvent 98% D)sample E2 (solvent 88% D)



Time resolved data Time resolved data acquisitionacquisition

switch to negative polarizationfrequency

negative dynamic nuclear polarization (DNP): 10 s

time resolved acquisition

• 200 spectra (in time framestime frames of 0.1 s length)

• several hundreds of 20 s long cycles are averaged

precise scattering intensity for each time frame

switch to positive polarizationfrequency

positive dynamic nuclear polarization (DNP): 10 s

time resolved acquisition



0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 0.1 st = 0.1 s

t [s]

0 10 20

PH

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 0.9 st = 0.9 s

t [s]

0 10 20

PH

Observation of polarized proton Observation of polarized proton clustersclusters

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 3.4 st = 3.4 s

t [s]

0 10 20

PH

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 10 st = 10 s

t [s]

0 10 20

PH

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 10.1 st = 10.1 s

t [s]

0 10 20

PH

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 10.9 st = 10.9 s

t [s]

0 10 20

PH

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 13.4 st = 13.4 s

t [s]

0 10 20

PH

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

Inte

nsité

[U.A

]

q [ Å-1 ]

t = 20 st = 20 s

t [s]

0 10 20

PH



Results

Experimental results: 200 spectra of neutron scattering

interpretation of the scattering curves

Fitting parameters : R1, R2, A, IInc and P

Conditions: • R1 and R2 are constant and time independent,

• Incoherent scattering independent of Q but dependent on time

• homogeneous polarization of the protons in the shell, dependent on time

R1 = 3.4 ÅR2 = 4.9 Å

P(t) IInc(t)

2

1312

321

3121 )()()()(),,( QRFRQRFRPQRFRAIRRQI soshsocinc

close protons



time dependent polarization gradient between the close and bulk protons

time dependence of polarization

close protons ~ exponential (SANS)

bulk protons ~ linear (NMR)

time [s]

0 5 10 15 20

pola

rizatio

n

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

close protons (fit)bulk protons (NMR)

exponential fit (1= 1.1 s, 2= 5.5 s)

close protonsclose protons versus

bulk protonsbulk protons

Europhys. Lett. 59 (2002) 62-67

characterization:sum of two exponential

t1 = 1.1s t2 =

5.5s

Time evolution of the polarization



Influence of the solvent deuteration

expected effect: faster diffusion of spin in solvent

Evolution of the close proton polarization for various solvent deuterations: 98%, 95% and 92% D

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.30.4

0.50.6

0.72

46

8101214161820I(

Q)

/ a.

u.

Q / A -1

time

/ se

c

EHBA, 95% deuterated solvent

0.45 0.50 0.55 0.60 0.65 0.70 0.75

1.3

1.4

1.5

1.6

1.7

1.8

1.9

0.30.4

0.50.6

0.72468101214161820

I(Q

) /

a.u.

Q / A -1

tim

e /

sec

EHBA, 92% deuterated solvent1.3 1.4 1.5 1.6 1.7 1.8

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

0.30.4

0.50.6

0.72

46

810

1214

161820I(

Q)

/ a.

u.

Q / A -1

time

/ se

c

EHBA, 98% deuterated solvent

0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

J. Kohlbrecher, Polarized Solid Targets, Honnef 2003 Dynamics Of Nuclear Spin Polarization J....

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Transcript of J. Kohlbrecher, Polarized Solid Targets, Honnef 2003 Dynamics Of Nuclear Spin Polarization J....