Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have...

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Gas-phase spin relaxation of 129 Xe Brian Saam Brian Saam Department of Physics T 1 = 100 hours! Workshop on Physics & Applications of Polarized Noble Gases University of Virginia, 19 May 2009

Transcript of Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have...

Page 1: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Gas-phase spin relaxation of 129Xe

Brian SaamBrian SaamDepartment of Physics

T1 = 100 hours!

Workshop on Physics & Applications of Polarized Noble GasesUniversity of Virginia, 19 May 2009

Page 2: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Filling the Polarization Bucket

γse

100%

PX zatio

n

PXe

Pola

ri

To maximize PX want γ >> Γ AND

Measured Γ1

0%To maximize PXe , want γse >> Γ AND <PRb> ≈ 1.

γse limited by available laser light. Measured with NMR T1

Γ =Relaxation

Goal: understand and minimize Γ.

Page 3: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Longitudinal Spin Relaxation in Noble Gases

1intrinsicgradientwall

1T

=Γ+Γ+Γ=Γ1

2|| BD ⊥∇=Γ

Container

K spin-rotation interaction:

B

20

gradient BD=Γ

Negligible in our experiments.1/Γwall = 0.1 – 1 h Xe

CK(R) N•K129Xe

interaction:

experiments.typically @ 30 G.

Density independent!Occurs during binary collision AND during the lifetime of a molecule.

Prior to work on dimers: Gas phase T1 typically a few tens of minutes for 129Xe; assumed dominated by wall interactions!

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Early Studies of Intrinsic 129Xe Relaxation

Γ∝ [Xe]

E.R. Hunt and H.Y. Carr, Phys. Rev. 130, 2302 (1963).

Assumes binary collisions only (transient dimers).

Lowest density studied is [Xe] = 50 amagats.

Γ 0 019 h/ t (T 52 h f 1 t X )Γbulk ≈ 0.019 h/amagat (T1 ≈ 52 h for 1 atm Xe)

Page 5: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Transient vs. Persistent Dimers

KXeXe

ptintrinsic Γ+Γ=ΓτpCK(R) N•K XeXe

KXX

binary collisions of duration τt≈ 1 ps.

Form/break up in 3-body collisions.

L t f lif ti 1

Transient Dimers Persistent DimersXeXe

τt 1 ps.

Γt ∝ [Xe].

Γt-1 ≈ 52 h•amagat: Hunt and

Last for lifetime τp ≈ 1 ns (until next collision).

Γt is independent of [Xe](for fixed gas composition)Carr (1963); Moudrakovski, et al.

(2001).

(for fixed gas composition).

Page 6: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Theory of Persistent-Dimer Relaxation*

[ ]( )Xe2222

p2

22

p κ⎟⎟⎞

⎜⎜⎛

⎟⎟⎞

⎜⎜⎛

=ΓτNcK [ ]( )e

13 2p

22p κ⎟⎠

⎜⎝ Ω+⎟

⎠⎜⎝ τh

Mean-squared spin-rotation interaction energy

Chemical Equilibrium CoefficientMean-squared spin-rotation interaction energy.

Power spectrum J(ω) for field fluctuations• τp ~ 10-9 seconds for [Xe] = 1 amagat.• ω/2π = 11 8 MHz for B = 1 T

[ ][ ][ ]XeXe

Xe2≡κ

Fraction of atoms bound in molecules, assumes [Xe2] << [Xe].

• ω/2π = 11.8 MHz for B0 = 1 T.• Can often assume Ω2τp

2 << 1 (fast-fluctuation limit).

Γp is independent of [Xe]; looks like wall relaxation!⇒∝ 1τ[Xe]

Key point for SEOP regime, where Ω2τp2<< 1:

*See: B. Chann, et al., Phys. Rev. Lett. 88, 113201 (2002).

⇒τp

Page 7: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Low-field (2 mT) Results*

( )⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎞⎜⎜⎝

⎛⎟⎟

⎜⎜

⎛=⎟

⎜⎜

⎛=Γ

]Xe/[]B[111

34

]Xe[3

4

Xe2

22

p2

22

pB

KK

rkNcNc

hh

κκτ

[ ] [ ]++ BXe1 kk

XevdWΓ = pure-Xe rate Correction for 2nd gas

[ ] [ ] L++= BXe BXep

kkτ

XeBB / kkr ≡

With:

• Need constant Γwall (asymptote).

• No observed [Xe] dependence forNo observed [Xe] dependence for fixed gas composition (inset).

• ΓvdW, Γwall, rB extracted from fits.Xe

Xe

*B. Chann, et al., Phys. Rev. Lett. 88, 113201 (2002).

• ΓvdW ≈ 0.25 h-1, ten times faster than binary collisions at 1 atm!

Xe

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High-field Experiments: Theory

222

⎟⎞

⎜⎛⎟

⎞⎜⎛ τNc

[ ]( )Xe213

22p

2p

2p κ⎟⎟⎠

⎞⎜⎜⎝

Ω+⎟⎟

⎜⎜

⎛=Γ

ττ

h

NcK

M ti fi ld d li tMagnetic-field decoupling term important for large Ω, small τp.

⎟⎞

⎜⎛⎟

⎞⎜⎛ 2222

22 K BNc μ Additional term due to chemical-⎟⎟⎠

⎞⎜⎜⎝

⎛Θ+⎟

⎠⎜⎜

⎝⊥22

60B

2 152

32

KK cBNc

hh

μ

Msr + Mcsa

Additional term due to chemicalshift anisotropy (CSA) interaction has dependence on .B0

2

( ) [ ]( )X2pcsasr κ⎟⎞

⎜⎛

Γτ

MM

M + M

( ) [ ]( )Xe21 2

p2

pcsasrp κ⎟

⎟⎠

⎜⎜⎝ Ω+

+=Γτ

MM

Page 9: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

High-Field Experiment: NMR Probe & Cell

1.5 T (17.7 MHz)

Field strengths B0:( )

4.7 T (55.3 MHz)

8.0 T (94.2 MHz)

14 1 T (166 MH )

6.7 cm diam spherical “measurement” cell.

Silicone-coated.14.1 T (166 MHz)

Contains no Rb (HP gas transferred in).

Long and robust wall relaxation times.

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129Xe Persistent-Dimer Relaxation: Results*

( ) [ ]( )Xe21 2

p2

pcsasrp κ⎟

⎟⎠

⎞⎜⎜⎝

Ω++=Γ

ττ

MM ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛Ω+

+=Γ 222

2csasr

p ]G[]G[2

α

ααkkMMκ

reparam.

Total gas density: ]N[]Xe[]G[ 2+=

Xe concentration (FIXED): ]G/[]Xe[≡α

Breakup coefficient: ]G[1p ατ k=−

High density: Γp independent of density.

Low density: magnetic-field T1 ≈ 5 h y gsupression of Γp.

Γp decreases for decreasing [Xe] at fixed total gas density [G].

1(wall time subtracted out).

*B.N. Berry-Pusey, et al., Phys. Rev. A 74, 063408 (2006); B.C. Anger, et al., Phys. Rev. A 78, 043406 (2008).

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100-Hour Gas-Phase T1 for 129Xe

Inferred wall relaxation time:T1 (wall) = 175 h!!

Obeys the Driehuys Axiom concerning HP xenon.

Page 12: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Quadratic Dependence on Applied Field

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛Ω+

+=Γ 222

2csasr

p ]G[]G[2

α

ααkkMMκ

⎠⎝

Combined interaction strength of SR and CSA

Data consistent with CSA interaction strength M csa proportional to B02.

Intercept is proportional to SR interaction strength M srIntercept is proportional to SR interaction strength M .

Characteristic crossover field B0 ≈ 16 T.

Page 13: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

So what about [Xe] = 1 amagat; B0 = 30 G?

Table II taken from: B.C. Anger, et al., Phys. Rev. A 78, 043406 (2008).

We’ve measured T1 = 5.75 h in a large 12 cm diam spherical borosilicate-glass cell (DMDCS-coated) at 30 G, 100°C. (Still limited by wall relaxation!)

Page 14: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Improvement to Flow-through 129Xe Polarizer*?

Long narrow cell (≈ 1 m long × 4 cm diam).g ( g )

[Xe] ≤ 1 amagat; use spectrally narrowed diode-laser array.

Counterpropagation of gas and laser light. p p g g g

Cryogenic (LN2) freeze out, separation, and storage of xenon (T1 ≈ 2.5 h @ 77 K).

*See talk B4.00002, tomorrow 10:42 am.

Goal: gas-phase storage cell (no cryogenics) with 3× storage time of frozen Xe having T1 ≈ 10 h. (Preliminary patent application filed.)

Page 15: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Summary

We have thoroughly (exhaustively) characterized intrinsic gas-phase T1-relaxation of 129Xe due to persistent Xe2 dimers—an important limit to production, accumulation, and storage of HP 129Xe.

Competes (and gets confused) with wall relaxation in many cases, because of

Transient-dimer contribution (binary collisions).

Persistent-dimer contribution (van der Waals molecules).

p ( g ) y ,density-independence of Γp.

Possibility of cryogen-free accumulation and storage with 2-3× longer storage times; significant improvement for state-of-the-art method in polarizing 129Xe.

Page 16: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Hyperpolarized Gas Research Group

FacultyBrian SaamDavid AilionGernot Laicher

Graduate StudentsBen Anger (postdoc at Leiden)Geoff Schrank (graduating Summer 2009)Geoff Schrank (graduating Summer 2009)Eric SorteZayd Ma

UndergraduatesBrittany Berry-Pusey (grad. at UCLA)Kimberly Butler (UU med. school)Laurel HalesAllison SchoeckOliver Jeong (HS student)Oliver Jeong (HS student)

Thanks to M.S. Conradi for numerous helpful discussions.

Page 17: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Room-Temperature Wall-Relaxation Rate vs. B0

Fast-fluctuation limitFast-fluctuation limit.

Intrinsic relaxation rate Γisubtracted out.

L t i fit i ldLorentzian fit yields correlation time for wall interaction of ≈ 4 ns.

Page 18: Gas-phase spin relaxation of Xegalileo.phys.virginia.edu/research/groups/spin... · Summary We have thoroughly (exhaustively) characterized intrinsic gas-phase T 1-relaxation of 129Xe

Simple Model for Surface Relaxation of Gases

Container of 129Xe with uniformly relaxing S S ⎞⎛

V, [Xe]

uniformly relaxing stable surface

Sv

VS⎟⎠⎞

⎜⎝⎛=Γ ηwall

η

1/Γwall typically ranges from 10 to 100 min for 129Xe in carefully prepared glass vessels

η ∝ surface relaxivity

vessels.

For ballistic collisions with a uniformly relaxing surface, Γwall is independent of gas density [Xe].