Polarized Proton Solid Target for RI beam experiments
description
Transcript of Polarized Proton Solid Target for RI beam experiments
Polarized Proton Solid Targetfor
RI beam experiments
M. Hatano University of TokyoH. Sakai University of TokyoT. Uesaka CNS, University of TokyoS. Sakaguchi CNS, University of TokyoT. Kawahara Toho UniversityA. Tamii RCNP, Osaka University
Developed at CNS, University of Tokyo
Takashi WakuiCYRIC, Tohoku University
Experiments with radioactive 6He beam at RIKEN
Outline
Polarizing methodOptical excitationCross polarization
Polarized proton target systemLaser, Microwave, NMRTarget chamber
Target performance during an experimentPolarization history during the experimentPolarization reversalRadiation damage
Introduction
Nuclear physics has been establishedfor 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 ingredientProduction spin polarization
Structure study of unstable nuclei
Polarized target using thin foil
Polarized target in a lower B and at a higher T
[P. Hautle]
(< 0.3 T) (> 100 K)
Polarize nuclei of interest
Optical pumping in superfluid helium
Collinear optical pumping technique
Projectile-fragmentation reaction
Tilted-foil technique
Pick-up reaction
Polarized target + RI beam
[T. Furukawa]
[T. Shimoda]
[H. Ueno]
[G. Goldring]
[M. Mihara]
Target material
Polarizable protons 6.3% by weightDensity cm-3
Concentration 0.01 mol%Target size 1 mm x 14 mm
Target material a crystal of aromatic molecules
pentacene (C22H14)
Host material
Guest material
naphthalene (C10H8)
22102.4
Polarizing process
1. Optical excitation (Laser)Electron alignment
2. Cross polarization (Microwave)Electron alignment Proton polarization
3. Diffusion of polarizationp in guest p in host
T1
Triplet state
(12%)
S0
S1
Singlet state
Laser(76%)
(12%)
population
+1
0
-1
S2
Optical excitationEnergy levels of pentacene (guest molecule)
xH0
Decay to T1 state (intersystem crossing)
Electron alignmentdepend on the angle between H and x-axis
Ψ ’=Ψ +Σ<Ψ |Hso |Ψ sk>
Wsk - WTΨ skT T
T
k
Pe =N(0) - N(-1)N(0) +N(-1)
=73%
100 s
Polarization transferCross polarization
Adiabatic Fast Passage of ESR
0
10
20
30
40
50
60
τ0
electronproton
effe
ctive
Lamor
freq
uenc
y(M
Hz)
time
e (rot. frame) p (lab. frame)
energyexchange
Hartmann-Hahncondition(Cross Polarization)
Effective Larmor frequency in the rotating frame
All spin packets can contribute to polarization transfer
R = I)
T1
+1
0
-1- 0.04
-0.02
0.00
0.02
0.04
0.06
320 325 330 335 340 345 350
Magnetic Field(mT)
Field Sweep(Adiabatically)
ESR spectrum
MicrowaveMicrowave
Polarizing process
1 Optical excitationelectron alignment
2 Cross polarizationpolarization transfer
3 Decay to the ground state4 Diffuse the polarization
to protons in host moleculesby dipolar interaction
ground state is diamagneticlong relaxation time
Repeating 1 4
T1
Triplet state
S0
S1
Singlet state
laser
+1
0
-1
S2
① ②③
④
Protons are polarized
100 s
Polarized Proton Target
Polarizing System
Target Chamber Target CrystalNaphthalene doped with pentaceneConcentration 0.01 mol%Thickness 1 mmDiameter 14 mm
100 KL o o p -g ap re so n a to r
N M R co ilC o ils fo r f ie ld sw e ep
C o u p lin g c o il
Aluminum shield(12 m)
Microwave Resonator
Coupling coil
Teflon
Copper platingcapacitanceTeflon
(25 m)Copper(4.4 m)
L = {(0.2 - 0.45) +1}0 2rz
r2
z2rz
r : radius, z : length
C = e 0 (w+t)(z+t)/nte : dielectric constant, 0: permittivityw : gap width, t : gap thickness, n : number of gaps
r=8 mmz=20 mm
Copper film loop-gap resonator (LGR)[B. T. Ghim et al., J. Magn. Reson A120 (1996) 72.]
Resonance frequency: 3.4 GHz
Thin film resonator Recoiled protons can reach to detectors
Experiments with Polarized TargetExperiments with radioactive 6He beam at RIKEN
Analyzing power (Ay) measurementin p+6He at 71 MeV
(July 2003, July 2005)
[S. Sakaguchi: poster session]
Polarization during Experiment
Magnetic field : 90 mTTemperature : 100 K
Polarization calibrationp+4He elastic scattering
Polarization reversalto reduce systematic uncertainties
pulsed NMR
Radiation damage
[July 2005]
Pmax = 19.7 (56)%Pav = 13.5 (39)%
Relative polarizationpulsed NMR
Polarization ReversalTo reduce systematic uncertainties
-30
-20
-10
0
10
20
30
0 10 20 30 40 50
Pol
ariz
atio
n [a
rb. u
nits
]
Time [hours]
Waste of time : 10 hours
polarization reversal bypulsed NMR method
= tH1
t = 2.2 s =180
75.0init
fin
P
PP
[July 2003]
July 2003July 2005
Experiment can go on without interruption for buildup
Relaxation Rate
BLTI
Proton Polarization during Buildup
A : Buildup rate : Relaxation ratePe : Average Population difference
I : Intrinsic (paramagnetic impurities)T : pentacene on photo-excited triplet state
(Laser ON)L : damage due to Laser irradiation
( power time : 0.0011(5) h-1/W・ h)B : radiation damage
Relaxation rate during experiment
Radiation Damage
0.1
1
0 2 4 6 8 10 12 14
Pol
ariz
atio
n [a
rb. u
nits
]
Time [hours]
before experiment (I+L) = 0.060(1) h-1
= 0.132(2) h-1
after experiment (I+L’+B)
4.1 108 /mm2
p+6He experiment (July 2003)
before experiment = 0.127(6) h-1
= 0.295(4) h-1
after experiment1.1 109 /mm2
= 0.060 (10) h-1
= 0.132 (12) h-1
p+6He experiment (July 2005)
Relaxation Rate during Experiment
B=0.0130 (4) h-1/108 mm-2
Laser power 200 mWBeam intensity 2x105 /sBeam spot size 10 mm
I+T+L @7 days B
contribution of each source
AnnealingFor a higher beam intensity
B should be reduced periodicallyby changing the target crystalby annealing
Relaxation rate clearly decreased at 200 K
Effect of Annealing
Polarization decreases
Crystal should be changed
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
Radiation damage
Protons were polarized in 90 mT at 100 K
Analyzing power (Ay) for p+6He elastic scattering
Polarization reversal by pulsed NMR method
Average value of p was 13.5% (July 2005)
75.0init
fin
P
PP
B=0.0130 (4) h-1/108 mm-2