Polarized Proton Solid Target for RI beam experiments

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Polarized Proton Solid TargetforRI beam
experiments
Developed at CNS, University of Tokyo
Takashi Wakui CYRIC, Tohoku University
M. Hatano University of Tokyo H. Sakai
University of Tokyo T. Uesaka CNS, University
of Tokyo S. Sakaguchi CNS, University of
Tokyo T. Kawahara Toho University A. Tamii
RCNP, Osaka University
Experiments with radioactive 6He beam at RIKEN
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Outline
Polarizing method Optical excitation Cross
polarization Polarized proton target
system Laser, Microwave, NMR Target
chamber Target performance during an
experiment Polarization history during the
experiment Polarization reversal Radiation
damage
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Introduction
Nuclear physics has been established for nuclei
close to the stability line
RI beam technique
Extend experimental nuclear physics to nuclei
far from the stability line
Spin polarization
Structure study of unstable nuclei
A key technical ingredient Production spin
polarization
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Structure study of unstable nuclei
Polarize nuclei of interest
Optical pumping in superfluid helium
T. Furukawa
Collinear optical pumping technique
T. Shimoda
Projectile-fragmentation reaction
H. Ueno
Tilted-foil technique
G. Goldring
Pick-up reaction
M. Mihara
Polarized target RI beam
Polarized target using thin foil
P. Hautle
Polarized target in a lower B and at a higher T
(gt 100 K)
(lt 0.3 T)
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Target material
Target material a crystal of aromatic molecules
Host material
naphthalene (C10H8)
Guest material
pentacene (C22H14)
Polarizable protons 6.3 by weight Density
cm-3 Concentration
0.01 mol Target size 1 mm x 14
mmf
Polarizing process

• Optical excitation (Laser)
• Electron alignment
• Cross polarization (Microwave)
• Electron alignment Proton polarization
• Diffusion of polarization
• p in guest p in host

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Optical excitation
Energy levels of pentacene (guest molecule)
100 ms
Decay to T1 state (intersystem crossing)
Electron alignment depend on the angle between
H and x-axis
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Polarization transfer
Cross polarization
Adiabatic Fast Passage of ESR
Microwave
Effective Larmor frequency in the rotating frame
(wR wI)
All spin packets can contribute to polarization
transfer
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Polarizing process
1 Optical excitation electron alignment 2
Cross polarization polarization transfer 3
Decay to the ground state 4 Diffuse the
polarization to protons in host molecules by
dipolar interaction
100 ms
ground state is diamagnetic
long relaxation time
Repeating 1 4
Protons are polarized
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Polarized Proton Target
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Polarizing System
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Target Chamber
Target Crystal Naphthalene doped with
pentacene Concentration 0.01 mol Thickness
1 mm Diameter 14 mm
100 K
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Microwave Resonator
Copper film loop-gap resonator (LGR) B. T. Ghim
et al., J. Magn. Reson A120 (1996) 72.
r8 mm z20 mm
Resonance frequency 3.4 GHz
Thin film resonator
Recoiled protons can reach to detectors
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Experiments with Polarized Target
Experiments with radioactive 6He beam at RIKEN
(July 2003, July 2005)
S. Sakaguchi poster session
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Polarization during Experiment
July 2005
Magnetic field 90 mT Temperature 100 K
Relative polarization
pulsed NMR
Polarization calibration
Polarization reversal to reduce systematic
uncertainties
Pmax 19.7 (56) Pav 13.5 (39)
pulsed NMR
Radiation damage
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Polarization Reversal
To reduce systematic uncertainties
July 2003
Waste of time 10 hours
polarization reversal by pulsed NMR method
q g t H1
July 2005
July 2003
t 2.2 ms
q180
Experiment can go on without interruption for
buildup
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Relaxation Rate
Proton Polarization during Buildup

• A Buildup rate
• Relaxation rate
• Pe Average Population difference

Relaxation rate during experiment
GI Intrinsic (paramagnetic impurities) GT
pentacene on photo-excited triplet state (Laser
ON) GL damage due to Laser irradiation (
power time 0.0011(5) h-1/Wh) GB
radiation damage
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Radiation Damage
p6He experiment (July 2003)
before experiment (GIGL)
G 0.060(1) h-1
4.1 108 /mm2
after experiment (GIGLGB)
G 0.132(2) h-1
GB 0.060 (10) h-1
p6He experiment (July 2005)
before experiment
G 0.127(6) h-1
1.1 109 /mm2
after experiment
G 0.295(4) h-1
GB 0.132 (12) h-1
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Relaxation Rate during Experiment
GB0.0130 (4) h-1/108 mm-2
contribution of each source
Laser power 200 mW Beam intensity 2x105
/s Beam spot size 10 mmf
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Annealing
For a higher beam intensity
GB should be reduced periodically
by changing the target crystal by annealing
Effect of Annealing
Relaxation rate clearly decreased at
200 K
Polarization decreases
Crystal should be changed
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Summary
Polarized proton target for RI beam experiments
developed at CNS, University of Tokyo
The target was used in the experiments
with radioactive 6He beam at
RIKEN
Analyzing power (Ay) for p6He elastic
scattering
Protons were polarized in 90 mT at 100 K
Average value of p was 13.5 (July 2005)
Polarization reversal by pulsed NMR method
Radiation damage
GB0.0130 (4) h-1/108 mm-2