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

How to polarize 3 He in liquid form 1. Brute force method >Polarized liquid is obtained by quickly melting polarized solid >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 >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 3 He solid >However, it’s difficult to make 3 He solid 2. Dynamic Nuclear Polarization (DNP) > spin-spin coupling between electron and nucleus > spin-spin coupling between electron and nucleus >Transferring polarization of electrons to neighboring nuclei >Transferring polarization of electrons to neighboring nuclei >able to obtain both positive and negative polarization >able to obtain both positive and negative polarization

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

French group applied DNP for polarizing liquid 3 He Used fluorocarbon beads containing electronic paramagnetic centers Used fluorocarbon beads containing electronic paramagnetic centers Polarization transfer process: electron → 19 F→ 3 He Polarization transfer process: electron → 19 F→ 3 He Obtained enhancements Obtained enhancements a. Positive: twice of TE signal at T=250mK, B=300G b. Negative: not mentioned A.Schuhl et al 1985 A.Schuhl et al 1985 DNP 3 He 19 F H TE 3 He

Our New DNP method for polarizing liquid 3 He Direct coupling of a unpaired electron and 3 He Direct coupling of a unpaired electron and 3 He >using spin-spin interaction of electron and nucleus Using unpaired electrons in a free radical Using unpaired electrons in a free radical Embedding the free radical into a porous material Embedding the free radical into a porous material Filling the porous material with liquid 3 He Filling the porous material with liquid 3 He Irradiating a microwave Irradiating a microwave  Free radical → TEMPO  Porous material → Zeolite

Zeolite and TEMPO NaY type zeolite (n=51) NaY type zeolite (n=51) Super Cage Max dia.: 13Å Window dia.: 7.4Å 4.7x10 19 super cages/g 3 He(dia.:3 Å ) → ≈80 3 He can get in one super cage TEMPO (2,2,6,6-tetramenthyl- piperidinyl-1-oxyle) TEMPO (2,2,6,6-tetramenthyl- piperidinyl-1-oxyle) Melting point: 36 º C Boiling point: 67 º C Molecule size: ~7Å sodalite cage double T6-ring Zeolite(Na n Al n Si (192-n) O 384 ·240H 2 O (n=48~76 ) HH CH 3 H3CH3C H3CH3C H H H H N O TEMPO 7Å7Å 7.4Å ESR signal of TEMPO in zeolite super cage

Embedding TEMPO to Zeolite Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n-pentane 2. Add zeolite to n-pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container 500 ºC Zeolite

Embedding TEMPO to Zeolite Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n-pentane 2. Add zeolite to n-pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container TEMPO n-pentane zeolite

Embedding TEMPO to Zeolite Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n-pentane 2. Add zeolite to n-pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container

Embedding TEMPO to Zeolite Preparation : Desiccate zeolite at 500 ºC for 8 hours Preparation : Desiccate zeolite at 500 ºC for 8 hours 1. Dissolve TEMPO in n-pentane 2. Add zeolite to n-pentane solution 3. Stir n-pentane solution for 8 hours in a sealed vessel 4. Evaporate n-pentane in a vacuum container R

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 Experimental cell Image of experimental chamber

Thermal equilibrium signal of 3 He TE signal of liquid 3 He T=1.42K,B ≒ 2.5T e - spin density :1.3×10 19 spins/cc e - spin density :1.3×10 19 spins/cc T=1.47K, B ≒ 2.5T T=1.47K, B ≒ 2.5T Low concentration of TEMPO e - spin density :4.5×10 18 spins/cc e - spin density :4.5×10 18 spins/cc T=1.54K, B ≒ 2.5T T=1.54K, B ≒ 2.5T High concentration of TEMPO Bulk 3 He (without zeolite) Symmetric signal when in zeoite Symmetric signal when in zeoite Narrower width for low spin density Narrower width for low spin density Bulk 3 He signal shows asymmetric shape Bulk 3 He signal shows asymmetric shape

TE signals fitted with Lorentzian TE signal of liquid 3 He T=1.42K,B ≒ 2.5T spin density :1.3×10 19 spins/cc spin density :1.3×10 19 spins/cc T=1.47K, B ≒ 2.5T T=1.47K, B ≒ 2.5T spin density :4.5×10 18 spins/cc spin density :4.5×10 18 spins/cc T=1.54K, B ≒ 2.5T T=1.54K, B ≒ 2.5T Low concentration High concentration Extent: 44.4ppm Bulk 3He(without zeolite) Red line shows the Lorentzian Center frequency of 3 He: 81.09MHz (in 2.5T) Extent: 202ppm

Relaxation time of liquid 3 He Fitting function S: area of the NMR signal time development of NMR signal of liquid 3 He inside zeolite T=1.44K, B=2.5T, spin density: 1.3×10 19 spin/cc Spin relaxation time:T 1 =330sec 3 He in zeolite with TEMPO

Positive enhancement by DNP ↑TE signal T=1.48K, B ≒ 2.5T T=1.48K, B ≒ 2.5T ↑max polarized signal B ≒ 2.5T B ≒ 2.5T observed positive enhancement observed positive enhancement S/S TE =2.34 spin density=4.5×10 18 (low concentration)

Negative enhancement by DNP ↑TE signal T=1.53K, B ≒ 2.5T T=1.53K, B ≒ 2.5T ↑max polarized signal B ≒ 2.5T B ≒ 2.5T observed negative enhancement S/S TE =-1.59 spin density=4.5×10 18

Micro wave frequency dependence fc: ESR center frequency of TEMPO(=70.22GHz) of TEMPO(=70.22GHz) spin density:1.3×10 19, B ≒ 2.5T at 2.5T expected ESR line width for TEMPO is 340MHz Observed line width was narrower than expected

Summary We obtained the thermal equilibrium signal of liquid 3 He in zeolite. We obtained the thermal equilibrium signal of liquid 3 He in zeolite. A narrow signal was observed with low concentration of TEMPO. A narrow signal was observed with low concentration of TEMPO. We measured relaxation time of 3 He in zeolite (It is a few minutes at 2.5T) We measured relaxation time of 3 He in zeolite (It is a few minutes at 2.5T) We obtained polarization enhancements for liquid 3 He in zeolite by DNP. We obtained polarization enhancements for liquid 3 He 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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Zeolite and its character Mineral which has a micro-porous structure, high hydrophobicity, thermostability and mostly used as a catalyst, ion exchanger, absorber Mineral which has a micro-porous structure, high hydrophobicity, thermostability and mostly used as a catalyst, ion exchanger, absorber (Na n Al n Si (192-n) O 384 ·240H 2 O (n=48~76 ) (Na n Al n Si (192-n) O 384 ·240H 2 O (n=48~76 ) Used (HSZ-300serise)TOSOH corporation Used (HSZ-300serise)TOSOH corporation Cation type: Na Cation type: Na SiO 2 /Al 2 O 3 (mol/mol): 5.5 SiO 2 /Al 2 O 3 (mol/mol): 5.5 Na2O(wt%): 12.5 Na2O(wt%): 12.5 U.C.C. by ASTM :24.63 U.C.C. by ASTM :24.63 NH3-TPD(mmol/g): - NH3-TPD(mmol/g): - Surface Area(BET, m2/g): 700 Surface Area(BET, m2/g): 700 Crystal Size(μm): 0.3 Crystal Size(μm): 0.3 Mean Particle Size(μm): 6 Mean Particle Size(μm): 6

Decrease of TEMPO in Zeolite Spin density :7.5×10 18 spin/cc Room temperature

n-pentane C 5 H 12 C 5 H 12 melting point: -131ºC melting point: -131ºC boiling point: 36.07ºC boiling point: 36.07ºC →0.13% Density of liquid 3 He in 1g zeolite in 1g zeolite23.1mg