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DNP for polarizing liquid 3 He

DNP for polarizing liquid 3 He. Hideaki Uematsu Department of Physics For Yamagata University PT group. Yamagata PT group(2006). Background of the study. Polarized 3 He targets have been used in various scattering experiments > in 3 He only neutron is polarized

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DNP for polarizing liquid 3 He

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  1. DNP for polarizing liquid 3He Hideaki Uematsu Department of Physics For Yamagata University PT group

  2. Yamagata PT group(2006)

  3. Background of the study • Polarized 3He targets have been used in various scattering experiments > in 3He only neutron is polarized > a good target for the study of neutron characteristics > studied only in gas targets • Advantages of polarizing liquid 3He >Density ⇒ gas:liquid=1:662 >Its fluidity may allow to make a polarized target with circulating polarized liquid 3He >Could be applied in many other fields (e.g. medical use, material science, chemistry, etc.)

  4. How to polarize 3He in liquid form • Brute force method >Polarized liquid is obtained by quickly melting polarized solid >55% polarization obtained in solid at 6.6T, 6mK, and 30bar, G.Bonfait et al. Phys.Rev.Lett. 53(1984)1092 >However, it’s difficult to make 3He solid • Dynamic Nuclear Polarization (DNP) >spin-spin coupling between electron and nucleus >Transferring polarization of electrons to neighboring nuclei >able to obtain both positive and negative polarization

  5. US group applied DNP for polarizing liquid 3He • Used powdered sucrose charcoal • Polarization transfer process: electron → 1H → 3He • Obtained positive enhancements • 1.18 times of TE signal amplitude at T=1.8K,B=182G • Measured relaxation time T1 was 1.02sec • L.W.Engel et al 1985 DNP

  6. 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 T=250mK, B=300G • Negative: not mentioned • A.Schuhl et al 1985 DNP 3He TE 19F 3He H

  7. Our New DNP method for polarizing liquid 3He • Direct coupling of a unpaired electron and 3He >using 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

  8. 7.4Å 7Å H H H H H H H3C CH3 H3C CH3 N O Zeolite and TEMPO Zeolite(NanAlnSi(192-n)O384·240H2O(n=48~76) • NaY type zeolite (n=51) • 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

  9. 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 500 ºC Zeolite

  10. 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 n-pentane TEMPO zeolite

  11. 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

  12. 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 R

  13. Image of experimental chamber Experimental cell 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

  14. Thermal equilibrium signal of 3He Bulk 3He (without zeolite) High concentration of TEMPO Low concentration of TEMPO TE signal of liquid 3He T=1.42K ,B≒2.5T e- spin density :1.3×1019spins/cc T=1.47K, B≒2.5T e- spin density :4.5×1018spins/cc T=1.54K, B≒2.5T • Bulk 3He signal shows asymmetric shape • Symmetric signal when in zeoite • Narrower width for low spin density

  15. TE signals fitted with Lorentzian Red line shows the Lorentzian Bulk 3He(without zeolite) High concentration Low concentration TE signal of liquid 3He T=1.42K ,B≒2.5T spin density :1.3×1019spins/cc T=1.47K, B≒2.5T spin density :4.5×1018spins/cc T=1.54K, B≒2.5T Extent: 202ppm Extent: 44.4ppm Extent: 202ppm Center frequency of 3He: 81.09MHz (in 2.5T)

  16. Fitting function S: area of the NMR signal Relaxation time of liquid 3He 3He in zeolite with TEMPO time development of NMR signal of liquid 3He inside zeolite T=1.44K, B=2.5T, spin density: 1.3×1019 spin/cc Spin relaxation time:T1=330sec

  17. ↑max polarized signal B≒2.5T Positive enhancement by DNP ↑TE signal T=1.48K, B≒2.5T spin density=4.5×1018(low concentration) observed positive enhancement S/STE =2.34

  18. ↑max polarized signal B≒2.5T Negative enhancement by DNP ↑TE signal T=1.53K, B≒2.5T spin density=4.5×1018 observed negative enhancement S/STE =-1.59

  19. 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 density:1.3×1019, B≒2.5T

  20. 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.

  21. Thank you for listening

  22. Zeolite and its character • Mineral which has a micro-porous structure, high hydrophobicity, thermostability and mostly used as a catalyst, ion exchanger, absorber • (NanAlnSi(192-n)O384·240H2O(n=48~76) • Used (HSZ-300serise)TOSOH corporation • Cation type: Na • SiO2/Al2O3(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(μm): 0.3 • Mean Particle Size(μm): 6

  23. Decrease of TEMPO in Zeolite Spin density :7.5×1018spin/cc Room temperature

  24. n-pentane • C5H12 • melting point: -131ºC • boiling point: 36.07ºC →0.13% Density of liquid 3He in 1g zeolite 23.1mg

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