an attempt toward dynamic nuclear polarization for liquid 3 he
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An attempt toward dynamic An attempt toward dynamic nuclear polarization for liquid nuclear polarization for liquid
33HeHe
1. Motivation of the study1. Motivation of the study22.. Polarizing Polarizing 33He in dense formHe in dense form3. DNP for liquid He3 3. DNP for liquid He3 33.. Doping with free radicalDoping with free radical4. ESR signals4. ESR signals5. Summary5. Summary
Takahiro IwataYamagata University
17/Nov./2005 @ PST2005
Motivation of the studyMotivation of the study
Polarized Polarized 33He targets have been employed in various He targets have been employed in various scattering experimentsscattering experiments• OnlyOnly neuron is polarized neuron is polarized in in 33HeHe• Good target for the study of neutron characteristics Good target for the study of neutron characteristics
Realized by the Realized by the optical pumpingoptical pumping technique technique • applied applied only for gas only for gas • Due to its gaseous form, the Due to its gaseous form, the density is limiteddensity is limited..• Its application is also limitedIts application is also limited
Polarized Polarized 33He in dense formHe in dense form will open a door to will open a door to extended applications.extended applications.• not only in particle physics, but also in other fields ( e.g. not only in particle physics, but also in other fields ( e.g.
medical applications, condensed matter physics, chemistry, …) medical applications, condensed matter physics, chemistry, …)
Possible ways for polarizingPossible ways for polarizing 33He in dense formHe in dense form
Brute force methodBrute force method• 55% polarization obtained in solid at 6.6T, 6mK and 30 bar, 55% polarization obtained in solid at 6.6T, 6mK and 30 bar, G.Bonfai
t et al., Phys.Rev.Lett. 53 (1984) 1092• Polarized liquid is also obtained by quickly melting the polarized solid.Polarized liquid is also obtained by quickly melting the polarized solid.• However, its application is limited due to the extreme condition.However, its application is limited due to the extreme condition.
Dynamic Nuclear Polarization (DNP)Dynamic Nuclear Polarization (DNP)• Direct couplingDirect coupling from electron system to from electron system to 33He, DelheiHe, Delhei
ji et al. in 1990ji et al. in 1990 diluted paramagnetic centers in liquid He3diluted paramagnetic centers in liquid He3 no polarization enhancement obtainedno polarization enhancement obtained
• Coupling between Coupling between 33He and polarized materialHe and polarized material with large surface area with large surface area
Nuclei polarized by DNP in material with large surface areaNuclei polarized by DNP in material with large surface area Polarization transfer to Polarization transfer to 33He in solid or liquid on the surfaceHe in solid or liquid on the surface
• A.Shuhl et al.,Phys.Rev.Lett. 54 (1985) 1952,A.Shuhl et al.,Phys.Rev.Lett. 54 (1985) 1952, Coupling toCoupling to 1919F in F in Teflon Teflon beads(d=2000A) polarized by DNP,beads(d=2000A) polarized by DNP,
originally existing paramagnetic centeroriginally existing paramagnetic center s s in Teflonin Teflon enhancement factor 2.0 for enhancement factor 2.0 for 33HeHe
• L.W.Engel and K.Deconde Phys.Rev. 33 (1986) 2035,L.W.Engel and K.Deconde Phys.Rev. 33 (1986) 2035, DNP of Liquid DNP of Liquid 33He in powdered He in powdered charcoalcharcoal
originally existing paramagnetic centers in charcoaloriginally existing paramagnetic centers in charcoal enhancement factor 1.18 for enhancement factor 1.18 for 33HeHe
• B.van den Brandt et al. (PSI-group), B.van den Brandt et al. (PSI-group), NIM A 356 (1995) 138-141NIM A 356 (1995) 138-141 beads ofbeads of Polyethylene Polyethylene, , TeflonTeflon,, ZeoliteZeolite Doping of free radicalDoping of free radical (TEMPO) (TEMPO)
• small polarization (P=2.5%) obtained with Teflon small polarization (P=2.5%) obtained with Teflon • 33He NMR signal changed (PE case)He NMR signal changed (PE case)• Doping was not successfulDoping was not successful for Teflon and Zeolite for Teflon and Zeolite
Coupling between He3 and Coupling between He3 and polarized materialpolarized material
Development of DNP for Development of DNP for polarizing He3 in liquidpolarizing He3 in liquid
Our idea: Our idea: • Direct coupling between a free radical and Direct coupling between a free radical and 33HeHe
The free radical is embedded into The free radical is embedded into porous materialporous material.. The porous material is filled with Liquid The porous material is filled with Liquid 33HeHe Coupling between the free radical and the Coupling between the free radical and the 33HeHe is is
induced by microwave.induced by microwave. Diffusion of Diffusion of 33He in the material would help the spin He in the material would help the spin
diffusion of diffusion of 33He.He.
The key issueThe key issue
One of the key issues:• Embedding a free radical in porous materials • The free radical molecules
① should be firmly trapped② should be well dispersed
Matching the cavity size of the porous material to the free radical molecule.
NaY type zeolite with a combination of TEMPO free radical.
Zeolite and TEMPOZeolite and TEMPO NaY zeolite( Na56 ) AL56Si139O3
84
NaY type zeoltie• Cavity(supercage):
13A(max. dia.) 7.4A(window dia.) 4.7x1019 cavities/g porosity: ~6%
TEMPO (2,2,6,6-tetramethyl-piperidinyl-1-oxyle)• Melting point: 36 oC.• Boiling point: 67 oC• Molecule size: 6~8A
3He• atomic radius : 1.5A
7.4
A
Si or Al
HH
CH3
CH3H3C
H3C
H
H
H
H
N
O
TEMPO
6 8
A
sodalite cage
supercage
double T6-ring
Doping processDoping process
stirrer
zeolite(7510mg) activated at 500 oC for 8 hoursTEMPO(24.8mg)n-pentane(300ml) boiling point: 36 oC
stirredfor 8 hours
in draft chamber
evaporating n-pentane
The amounts to give1.6 x 1019 spins/cc, ¼ of super cagesoccupied with TEMPO
This method is used in studies of unstable radicals
ESR signalsESR signals
ESR signal of TEMPO in zeolite• a little broader than tha
t in ethanol• peaks still separated
TEMPO molecules are dispersed at some levelTEMPO
in ethanol
TEMPOin zeolite
Intensity of the ESR signalin the air at room temperature
TEMPO is firmly trapped in zeolite
Stability of TEMPO in zeoliteStability of TEMPO in zeolite
Intensity of the ESR signalin vacuum at room temperature
in the air
in vacuum
Measurements of intensity variation of the ESR signal
Stability of TEMPO in PEStability of TEMPO in PE
Intensity of TEMPO in PEin the air at room temperature
PE foil(0.1 mm thick) doped with TEMPO by diffusion
The ESR intensity decreases with a time constant of ~5 hours
Reasons• TEMPO trapped in the amorph
ous part• PE molecule movable at room
temp. (Tg=205K) enhance diffusion • evaporation from surface
Zeolite case• TEMPO trapped in the superc
age which is a part of firm structure.
Next stepNext step
Filling the zeolite with liuid 3He and trying to do DNP
@2.5T, 0.6K jobs
• installing the sample cell into the cryostat (final assembly needed)
• setting the 3He gas handling system (almost ready)
• NMR system for 3He (tuning required)• system for DNP (ready)
Summary Summary
DNP for 3He in dense form will open the door to various applications.
DNP for liquid 3He is pursued through the direct interaction between 3He and a free radical molecule embedded in cavities of zeolite.
We have prepared the zeolite doped with TEMPO free radical.
Being well dispersed, the TEMPO molecules are firmly trapped in zeolite.
We are ready to make DNP for liquid 3He in the zeolite.
Backup SlidesBackup Slides
polarized polarized 33He circulation schemeHe circulation scheme
pump system
holdign magnet detector system
target cell
beam
microwavezeolite doped
with free radical
pol. magnet
Characteristics of the zeolite for the testCharacteristics of the zeolite for the test
320NAA Cation type: Na SiO2/ALO3(mol/mol):5.5 Na2O(wt%):12.5 U.C.C. by ASTM: 24.63 NH3-TPD(mmol/g): - Surface Area (BET,m2/g) 700 Crystal Size: 0.3 micro meter Mean Particle Size: 6 micro meter density: 1.38g/cc lattice constant: 24.2-25.1 A supercage density: 6.6x1019 cages/cc
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