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