An attempt toward dynamic nuclear polarization for liquid 3 He 1. Motivation of the study 2 ． Polarizing 3 He in dense form 3. DNP for liquid He3 3 ． Doping with free radical 4. ESR signals 5. Summary Takahiro Iwata Yamagata University PST2005

Motivation of the study Polarized 3 He targets have been employed in various scattering experiments Polarized 3 He targets have been employed in various scattering experiments Only neuron is polarized in 3 HeOnly neuron is polarized in 3 He Good target for the study of neutron characteristicsGood target for the study of neutron characteristics Realized by the optical pumping technique Realized by the optical pumping technique applied only for gasapplied only for gas Due to its gaseous form, the density is limited.Due to its gaseous form, the density is limited. Its application is also limitedIts application is also limited Polarized 3 He in dense form will open a door to extended applications. Polarized 3 He in dense form will open a door to extended applications. not only in particle physics, but also in other fields ( e.g. medical applications, condensed matter physics, chemistry, … )not only in particle physics, but also in other fields ( e.g. medical applications, condensed matter physics, chemistry, … )

Possible ways for polarizing 3 He in dense form Brute force method Brute 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.Bonfait 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 coupling from electron system to 3 He, Delheiji et al. in 1990Direct coupling from electron system to 3 He, Delheiji et al. in 1990 diluted paramagnetic centers in liquid He3 diluted paramagnetic centers in liquid He3 no polarization enhancement obtained no polarization enhancement obtained Coupling between 3 He and polarized material with large surface areaCoupling between 3 He and polarized material with large surface area

Nuclei polarized by DNP in material with large surface area Nuclei polarized by DNP in material with large surface area Polarization transfer to 3 He in solid or liquid on the surface Polarization transfer to 3 He 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 to 19 F in Teflon beads(d=2000A) polarized by DNP, Coupling to 19 F in Teflon beads(d=2000A) polarized by DNP, originally existing paramagnetic center ｓ in Teflon originally existing paramagnetic center ｓ in Teflon enhancement factor 2.0 for 3 He enhancement factor 2.0 for 3 He 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 3 He in powdered charcoal DNP of Liquid 3 He in powdered charcoal originally existing paramagnetic centers in charcoal originally existing paramagnetic centers in charcoal enhancement factor 1.18 for 3 He enhancement factor 1.18 for 3 He B.van den Brandt et al. (PSI-group), NIM A 356 (1995) B.van den Brandt et al. (PSI-group), NIM A 356 (1995) beads of Polyethylene, Teflon, Zeolite beads of Polyethylene, Teflon, Zeolite Doping of free radical (TEMPO) Doping of free radical (TEMPO) small polarization (P=2.5%) obtained with Teflonsmall polarization (P=2.5%) obtained with Teflon 3 He NMR signal changed (PE case) 3 He NMR signal changed (PE case) Doping was not successful for Teflon and ZeoliteDoping was not successful for Teflon and Zeolite Coupling between He3 and polarized material

Development of DNP for polarizing He3 in liquid Our idea: Our idea: Direct coupling between a free radical and 3 HeDirect coupling between a free radical and 3 He The free radical is embedded into porous material. The free radical is embedded into porous material. The porous material is filled with Liquid 3 He The porous material is filled with Liquid 3 He Coupling between the free radical and the 3 He is induced by microwave. Coupling between the free radical and the 3 He is induced by microwave. Diffusion of 3 He in the material would help the spin diffusion of 3 He. Diffusion of 3 He in the material would help the spin diffusion of 3 He.

The key issue One of the key issues: Embedding a free radical in porous materials The free radical molecules ① should be firmly trapped ② 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 TEMPO NaY zeolite ( Ｎａ ５６ ) ＡＬ ５６ Ｓｉ １ ３９ Ｏ ３８４ NaY type zeoltie Cavity(supercage): 13A(max. dia.) 7.4A(window dia.) 4.7x10 19 cavities/g porosity: ~6% TEMPO (2,2,6,6- tetramethyl-piperidinyl-1- oxyle) Melting point: 36 o C. Boiling point: 67 o C Molecule size: 6~8A 3 He atomic radius : 1.5A Si or Al HH CH 3 H3CH3C H3CH3C H H H H N O TEMPO sodalite cage supercage double T6-ring

Doping process stirrer zeolite(7510mg) activated at 500 o C for 8 hours TEMPO(24.8mg) n-pentane(300ml) boiling point: 36 o C stirred for 8 hours in draft chamber evaporating n-pentane The amounts to give 1.6 x spins/cc, ¼ of super cages occupied with TEMPO This method is used in studies of unstable radicals

ESR signals ESR signal of TEMPO in zeolite a little broader than that in ethanol peaks still separated TEMPO molecules are dispersed at some level TEMPO in ethanol TEMPO in zeolite

Intensity of the ESR signal in the air at room temperature TEMPO is firmly trapped in zeolite Stability of TEMPO in zeolite Intensity of the ESR signal in vacuum at room temperature in the air in vacuum Measurements of intensity variation of the ESR signal

Stability of TEMPO in PE Intensity of TEMPO in PE in 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 amorphous part PE molecule movable at room temp. (Tg=205K)  enhance diffusion evaporation from surface Zeolite case TEMPO trapped in the supercage which is a part of firm structure.

Next step Filling the zeolite with liuid 3 He and trying to do 0.6K jobs installing the sample cell into the cryostat (final assembly needed) setting the 3 He gas handling system (almost ready) NMR system for 3 He (tuning required) system for DNP (ready)

Summary DNP for 3 He in dense form will open the door to various applications. DNP for liquid 3 He is pursued through the direct interaction between 3 He 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 3 He in the zeolite.

Backup Slides

polarized 3 He circulation scheme pump system holdign magnet detector system target cell beam micro wave zeolite doped with free radical pol. magnet

Characteristics 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: 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: A supercage density: 6.6x10 19 cages/cc