DNP for polarizing liquid 3He

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DNP for polarizing liquid 3He

• Akira Tanaka
• Department of Physics
• For Yamagata University
• PT group

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Yamagata PT group(2006)
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Background of the study

• Polarized 3He targets have been used in various
  scattering experiments
• gt in 3He only neutron is polarized
• gt a good target for the study of neutron
  characteristics
• gt studied only in gas targets
• Advantages of polarizing liquid 3He
• gtDensity gasliquid1662
• gtIts fluidity may allow to make a polarized
  target with circulating polarized liquid 3He
• gtCould be applied in many other fields
• (e.g. medical use, material science, chemistry,
  etc.)

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How to polarize 3He in liquid form

• Brute force method
• gtPolarized liquid is obtained by quickly
  melting polarized solid
• gt55 polarization obtained in solid at 6.6T,
  6mK, and 30bar, G.Bonfait et al.
  Phys.Rev.Lett. 53(1984)1092
• gtHowever, its difficult to make 3He solid
• Dynamic Nuclear Polarization (DNP)
• gtspin-spin coupling between electron and
  nucleus
• gtTransferring polarization of electrons to
  neighboring nuclei
• gtable to obtain both positive and negative
  polarization

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US group applied DNP for polarizing liquid 3He

• Used powdered sucrose charcoal
• Polarization transfer process
• electron ? 1H ? 3He
• Obtained positive enhancements
• 18 plus of TE signal amplitude at T1.8K,B182G
• Measured relaxation time T1 was 1.02sec
• L.W.Engel et al 1985

DNP
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French group applied DNP for polarizing liquid 3He

• Used fluorocarbon beads containing electronic
  paramagnetic centers
• Polarization transfer process electron ? 19F?3He
• Obtained enhancements
• Positive twice of TE signal at T250mK, B300G
• Negative not mentioned
• A.Schuhl et al 1985

DNP
3He
TE
19F
3He
H
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Our New DNP method for polarizing liquid 3He

• Direct coupling of a unpaired electron and 3He
• gtusing spin-spin interaction of electron and
  nucleus
• Using unpaired electrons in a free radical
• Embedding the free radical into a porous material
  
• Filling the porous material with liquid 3He
• Irradiating a microwave
• Free radical ? TEMPO
• Porous material ? Zeolite

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Zeolite and TEMPO
Zeolite(NanAlnSi(192-n)O384240H2O(n4876)

• NaY type zeolite (n51)
• Super Cage
• Max dia. 13Å
• Window dia. 7.4Å
• 4.7x1019 super cages/g
• 3He(dia.3Å) ? 80 3He can get in one super cage
• TEMPO(2,2,6,6-tetramenthyl-piperidinyl-1-oxyle)
• Melting point 36 ºC
• Boiling point 67 ºC
• Molecule size 7Å

sodalite cage
super cage
double T6-ring
TEMPO
ESR signal of TEMPO in zeolite
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Embedding TEMPO to Zeolite

• Preparation Desiccate zeolite at 500 ºC for 8
  hours
• Dissolve TEMPO in n-pentane
• Add zeolite to n-pentane solution
• Stir n-pentane solution for 8 hours in a sealed
  vessel
• Evaporate n-pentane in a vacuum container

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Embedding TEMPO to Zeolite

• Preparation Desiccate zeolite at 500 ºC for 8
  hours
• Dissolve TEMPO in n-pentane
• Add zeolite to n-pentane solution
• Stir n-pentane solution for 8 hours in a sealed
  vessel
• Evaporate n-pentane in a vacuum container

TEMPO
zeolite
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Embedding TEMPO to Zeolite

• Preparation Desiccate zeolite at 500 ºC for 8
  hours
• Dissolve TEMPO in n-pentane
• Add zeolite to n-pentane solution
• Stir n-pentane solution for 8 hours in a sealed
  vessel
• Evaporate n-pentane in a vacuum container

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Embedding TEMPO to Zeolite

• Preparation Desiccate zeolite at 500 ºC for 8
  hours
• Dissolve TEMPO in n-pentane
• Add zeolite to n-pentane solution
• Stir n-pentane solution for 8 hours in a sealed
  vessel
• Evaporate n-pentane in a vacuum container

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Experimental setup

• Experimental cell made of a PET tube and a VCR
  gas connector
• Volume 2.5cc
• Experimental cell filled with zeolite tightly
  and quickly

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Thermal equilibrium signal of 3He
Low concentration
High concentration
Bulk 3He
TE signal of liquid 3He T1.42K ,B?2.5T
spin density 1.31019spins/cc T1.47K, B?2.5T
spin density 4.51018spins/cc T1.54K, B?2.5T

• Bulk 3He signal shows asymmetric shape

• Symmetric signal when in zeoite

• Narrower width for low spin density

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TE signals fitted with Lorentzian
Red line shows the Lorentzian
Low concentration
High concentration
Bulk 3He
FWHM
FWHM
FWHM
spin density 1.31019spins/cc T1.47K, B?2.5T
spin density 4.51018spins/cc T1.54K, B?2.5T
TE signal of liquid 3He T1.42K ,B?2.5T
FWHM16.4KHz
FWHM16.4KHz
FWHM3.6KHz
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Relaxation time of liquid 3He
Fitting function
S area unit of the NMR signal
Bulk 3He
time development of NMR signal of bulk liquid
3He T0.86K, B2.5T
Spin relaxation timeT1210sec
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Relaxation time of liquid 3He
3He in zeolite
time development of NMR signal of liquid 3He
inside zeolite T1.44K, B2.5T, spin density
1.31019 spin/cc
Spin relaxation timeT1330sec
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Positive enhancement by DNP
?TE signal T1.48K, B?2.5T
?max polarized signal B?2.5T
spin density4.51018
observed positive enhancement S/STE 2.34
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Negative enhancement by DNP
?TE signal T1.53K, B?2.50T
?max polarized signal B?2.499T
spin density4.51018
observed negative enhancement S/STE -1.59
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Micro wave frequency dependence
fc ESR center frequency of TEMPO(70.22GHz)
at 2.5T expected ESR line width for TEMPO is
340MHz
Observed line width was narrower than expected
spin density1.31019, B?2.5T
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Summary

• We obtained the thermal equilibrium signal of
  liquid 3He in zeolite.
• A narrow signal was observed with low
  concentration of TEMPO.
• We measured relaxation time of 3He in zeolite (It
  is a few minutes at 2.5T)
• We obtained polarization enhancements for liquid
  3He in zeolite by DNP.
• The enhancements were larger than ever before
  (obtained by DNP).
• They may be improved by tuning the conditions.

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