SPIN 2004Oct. 14, 2004

W. Kim, S.S. Stepanyan, S. Woo, M. Rasulbaev, S. Jin

(Kyungpook National University)S. Korea

Polarization Measurements of the Target with water and DPPH

3He

Optical Pumping Mechanism

Spin exchange with optically pumped alkali metal rubidium vapor.

Optical Pumping Procedure

cell

optics

Diode Laser

Oven (160 oC)

pickup coil

RF drive coils

Instrument Control

Coils providing uniform magnetic field

xMxy

M

MzH0

y

RF Coil

Nuclear Magnetic Resonance

If an RF field of frequency equal to Larmor frequency is applied orthogonal to H0 holding field , the particles can undergo reversal of their magnetic dipole moment orientation.

0 0H

Resonance condition:

02

Adiabatic Fast Passage

AFP sweep is produced sweeping main magnetic field through the resonance up and down the spin rotates an angle approaching 180° as the process is adiabatic.

01

1 1

1 1 dHH

T H dt

T1 – spin-lattice relaxation time;

H1 – magnetic component of RF field;

H0 – Holding magnetic field amplitude;

– gyromagnetic ratio;

NMR Setup Schematic

NMR Setup for 3He Target at KNU

Helmholtz coil system NMR Electronics

Optics Setup

Optics

NMR signal creation program

Laser control program

NMR measurement program

Test of the NMR Setup

Loop ~ NMR setup: 3 metersPhase: 40.00 degrees External RF radiation generator turned off

NMR setup as a Receiver

Vol

tage

indu

ced

in th

e pi

ck-u

p co

ils

[mV

]

Holding Magnetic Field [G]

Q-curve

Q-curve of pick-up coil circuit fitted with Lorentzian.

RF signal amplitude adjustments

Calibration Constant for Polarization Measurements (1)

S k M k n P

S : amplitude of the lock-in amplifier signal k : prop. Constant, taking a count gains, losses in the cables, …μ : magnetic moment of the sample.n : density of the spins .P : polarization of the sample

The signal induced in the pick-up coils by the AFP sweep and detected by the lock-in amplifier is proportional to the macroscopic magnetization M of the sample;

The ratio of the Helium NMR signal height SHe to the water NMR signal height Sw

He He He He He

w w p p w

S G n P

S G n P

Calibration Constant for Polarization Measurements (2)

1 with, pHe w

He w w p wHe w He He

S GP C C n P

n S G

: amplitude of the water signal : amplitude of the Helium signal , : magnetic moments of protons in water and 3He nucleus.

wS

HeS

p He

Polarization of the He target proportional to magnetization.

Polarization Calculation

9 9tanh tanh 7.4 10 0.074.102 2

pw

w w w

B h hP

kT kT kT

1181067.2 Ts

The value of the water sample polarization is calculated from Boltzman statistics:

Tw : water temp [K]

B : Resonance Holding field

ν (=91kHz) : RF field frequency

1 Amagat (amg) =

amplitude of the water signal extracted from the fit of the average NMR data.

31910689.2 cm

6wS V

22 3(6.67 0.05) 10 2482 2 Amagatspn cm

DPPH (Solid 2.2-Diphenil-1-Picrylhydrazyl) for Calibration of Polarization.

Uncertainty AFP Polarization measurements 7%

Helium density < 5%

Thermal signal < 1%

Amplitude measurement < 2.5%

Gains <1%

Experimental g-factor for DPPH : g=2.039±0.023 very close to electron

Used DPPH (5gr, 1cm3 powder) as material for calibration

10 turns of Pickup coils around DPPH

Holding Field for 91kHz is less than 0.5G during AFP sweep

BE g B h h

gB

91 0.5

h B

kHz B G

DPPH Signal

X ChanelAbsorption

Y ChanelDispersion

Water Signal

Summary

NMR system constructed and calibrated for polarization measurements of the polarized 3He Target with AFP method.

Signal-to-noise ratio improved by making coils for NMR setup for polarization measurements.

Measurements performed with DPPH and water