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